bluuebunny/crossref_metadata_2025 huggingface dataset:
Limited cardiac preload reserve in conscious cirrhotic rats
Authors: Ingles A. C. , Hernandez I. , Garcia-Estan J. , Quesada T. , Carbonell L. F.
Published: December 2017

In conscious rats with experimental cirrhosis without ascites, we have studied whether there is a limited cardiac preload reserve by performing cardiac output (CO) curves. CO was determined by thermodilution at basal, 5, 7.5, and 10 cmH2O of right atrial pressure (RAP). RAP was elevated by dextran infusion (1 ml/min iv, 30 min). CO curves were performed by plotting changes in CO with changes in RAP. In the basal state, cirrhotic rats showed a hyperdynamic circulation defined by increased CO and stroke volume, decreased total peripheral resistances, and normotension without changes in heart rate. Blood volume was also elevated in cirrhotic rats compared with the control animals. Between the limits of RAP studied, the CO curve of control rats presented a typical ascending limb. In contrast, the CO curve of the cirrhotic animals showed first an ascending shifted upward limb and afterward a descending limb. These alterations were accompanied by changes in the inotropic state as measured as left ventricular (LV) peak dP/dt in hexamethonium-pretreated animals submitted to the same volume loads described above. With the same increases in RAP, LV dP/dt changed, in every group, in a manner similar to CO. The results of the present study indicate that cirrhotic rats with high blood volume and hyperdynamic circulation show, in the steady state, a limited preload reserve. The partial utilization of the preload reserve can make the cirrhotic heart unable to modulate cardiac performance with changes in loading conditions, thus determining a state of heart failure.
Paradoxical constriction to platelets by arteries from rats with pulmonary hypertension
Authors: Ashmore R. C. , Rodman D. M. , Sato K. , Webb S. A. , O'Brien R. F. , McMurtry I. F. , Stelzner T. J.
Published: December 2017

We recently described the early appearance of pulmonary hypertension in the fawn-hooded rat (FHR), an animal with platelet storage pool disease also known to develop systemic hypertension at later ages. Since mediators released from aggregating platelets influence vascular tone, we hypothesized that platelet-mediated pulmonary vascular responses in FHR may be abnormal and potentially linked to the mechanism of pulmonary hypertension. To test this we examined reactivity of isolated pulmonary arteries (PA) and thoracic aortas (Ao) from young FHR with moderately severe pulmonary hypertension but normal systemic pressures. These vessels were compared with PA and Ao from control Sprague-Dawley rat (SDR). Aggregating platelets (1,000-40,000 platelets/mm3) from FHR caused dilation of SDR PA and Ao but constriction of FHR PA and Ao. Qualitatively similar responses were also observed with platelets isolated from SDR implying that abnormal responses were not simply due to the storage pool deficiency in FHR. Response to the platelet-derived endothelium-dependent vasodilator ADP was markedly impaired in FHR PA and mildly impaired in FHR Ao. Endothelium-dependent dilation to acetylcholine, but not to A23187, was mildly impaired in FHR PA while responses to both dilators were normal in FHR Ao. Endothelium-independent dilation to sodium nitroprusside was normal in both FHR PA and Ao. Constrictor sensitivity to serotonin, but not to the thromboxane A2 mimetic U-46619, was increased in FHR PA while responses to both constrictors were normal in FHR Ao. In summary, PAs from FHR with spontaneous pulmonary hypertension exhibit paradoxical constriction to both normal and storage pool deficient platelets.(ABSTRACT TRUNCATED AT 250 WORDS)
Hemoglobin potentiates oxidant injury in isolated rat lungs
Authors: Seibert A. F. , Taylor A. E. , Bass J. B. , Haynes J.
Published: December 2017

Isolated perfused rat lungs were subjected to oxidant injury induced by tert-butyl hydroperoxide (t-buOOH), which caused a significant increase in capillary permeability as assessed by the change in the capillary filtration coefficient. t-buOOH caused an increase in the change in the capillary filtration coefficient (delta Kfc) of 0.27 +/- 0.05 ml.min.cmH2O-1.100 g lung tissue-1 (mean +/- SE) that was accompanied by an increase in thiobarbituric acid reactive products of lipid peroxidation in the lung perfusate. The addition of hemoglobin to the perfusate potentiated t-buOOH-induced lung injury as evidenced by a significantly greater (P = 0.007) delta Kfc of 0.43 +/- 0.05. t-buOOH also caused hemoglobin to release large quantities of free iron in vitro. The potentiation of t-buOOH-induced lung injury by hemoglobin was prevented by apotransferrin as evidenced by a significant reduction (P = 0.001) in delta Kfc to 0.13 +/- 0.02. No statistically significant (P greater than 0.05) changes in segmental resistances or pulmonary vascular pressures occurred in any of the lungs injured with t-buOOH when compared with time controls. These results demonstrate that t-buOOH causes an oxidant injury in isolated rat lungs that can be potentiated by free iron released from hemoglobin.
Intracranial pressures and O2 extraction in conscious sheep during 72 h of hypoxia
Authors: Curran-Everett D. C. , Iwamoto J. , Meredith M. P. , Krasney J. A.
Published: December 2017

High-altitude cerebral edema may occur within several days after a rapid ascent to altitude. However, the mechanisms that produce this potentially lethal condition are unclear. This experiment assessed systemic arterial and intracranial pressures (n = 22) and cerebral blood flow per unit cerebral O2 consumption (Qc/cVo2) and cerebral O2 extraction fraction (cEo2) (n = 9) in conscious sheep before and during 72 h of normobaric hypoxia (arterial O2 tension approximately 40 mmHg, oxygen saturation in arterial blood approximately 50%). Qc/cVo2 and cEo2 were calculated from systemic arterial and cerebral venous O2 contents. Wet-to-dry brain weight ratios were calculated during normoxia (n = 4) or after 72 h of hypoxia (n = 5) in additional sheep. Intracranial pressures did not change during hypoxia (+ 1.3 to +1.8 mmHg, P = 1.0); however, estimated intracranial capillary hydrostatic pressure may have increased 1-20 mmHg depending on the arterial-to-downstream resistance ratio. During the 72 h of hypoxia, Qc/cVO2 doubled (P = 0.02) and cEo2 tended to decrease (5% absolute, P = 1.0). Regional wet-to-dry brain weight ratios after 72 h of hypoxia were 4-13% greater than their respective ratios during normoxia (0.001 less than P less than or equal to 0.05); indirect evidence suggests that this increased brain water content was extravascular. The sheep may be an appropriate model for the further study of high-altitude cerebral edema.
EDRF released from microvascular endothelial cells dilates arterioles in vivo
Authors: Koller A. , Seyedi N. , Gerritsen M. E. , Kaley G.
Published: December 2017

Microvascular endothelial cells (MECs) from rat epididymal fat pad were isolated and cultured in vitro on Cytodex 3 microcarrier beads. In Krebs-suffused cremaster muscle of pentobarbital-anesthetized rats arteriolar diameters (mean control diam 20.9 +/- 0.9 micron) were measured using image shearing video microscopy. Two lines of suffusate (1.5 ml/min each) were established; one contained a column of microcarrier beads only (no cells in line; NC) the other contained a 1-ml column of MECs grown on beads (through cells; TC). The muscle preparation and the MECs were first treated with indomethacin (Indo; 28 microM). Indo treatment blocked arteriolar dilation to A23187 (1 microM) and arachidonic acid (AA; 0.25 microM) administered into the NC line. A 4.0 +/- 0.6 micron increase in arteriolar diameter was observed, however, when A23187 (but not AA) was infused through the TC line containing Indotreated MECs on beads. The A23187-elicited dilation was abolished by the introduction of NG-monomethyl-L-arginine (L-NMMA; 200 microM) into the TC line. Administration of atropine (2 microM) onto the cremaster muscle via the NC line inhibited the dilations in response to acetylcholine (ACh; 2.7 microM) given through the NC line. Infusion of ACh through the TC line onto the atropine-treated cremaster muscle, however, elicited a 5.8 +/- 1.3 micron increase in arteriolar diameter, a response that was blocked by prior administration of L-NMMA into the TC line. Arteriolar dilation induced by adenosine (0.5 microM) or sodium nitroprusside (0.5 microM) applied via the NC or TC line was unaffected by L-NMMA.(ABSTRACT TRUNCATED AT 250 WORDS)
Enhanced renal PGE2 in hypertensives with increased red cell Na(+)-Li+ countertransport
Authors: Arrazola A. , Diez J.
Published: December 2017

In this study, maximal velocities of Na(+)-Li+ countertransport were measured in red blood cells of 50 untreated essential hypertensives and 30 normotensive controls. In addition, urinary excretion of renal prostaglandins (PG) and plasma renin activity (PRA) was measured in each subject. Maximal velocity of Na(+)-Li+ countertransport was above the upper limit in controls of 525 mumol.l cell-1.h-1 in seven patients and was normal in the remaining patients. Patients with increased countertransport did not differ significantly from controls and from patients with normal countertransport with regard to urinary excretion of 6-keto-PGF1 alpha (the stable metabolite of prostacyclin) and thromboxane B2 (TxB2) (the stable metabolite of thromboxane A2). In contrast, mean values of PGE2 were significantly higher (P less than 0.01) in patients with increased countertransport (411 +/- 39 pg/min) compared with patients with normal countertransport (181 +/- 15 pg/min) and controls (146 +/- 13 pg/min). In addition, six patients with increased countertransport exhibited urinary levels of PGE2 higher than the upper limit in controls. Hypertensives with increased countertransport showed enhanced PRA when compared with the remaining patients (2.96 +/- 0.50 vs. 1.30 +/- 0.52 ng.ml-1.h-1, P less than 0.05) and with controls (1.86 +/- 0.08 ng.ml-1.h-1, P less than 0.05). Finally, the relationship between PGE2 and PRA was found to be significant in patients with increased countertransport (r = 0.776, P less than 0.05). These results indicate that renal synthesis of PGE2 is enhanced in essential hypertensives with increased Na(+)-Li+ countertransport activity and hyperreninemia.
Flow modulation of agonist (ATP)-response (Ca2+) coupling in vascular endothelial cells
Authors: Dull R. O. , Davies P. F.
Published: December 2017

ATP-induced increases of intracellular calcium concentration ([Ca2+]i) were measured as a function of flow rate in single cell recordings within a confluent endothelial cell monolayer. Although flow and its associated shear stress did not per se significantly alter basal [Ca2+]i, ATP-induced [Ca2+]i was exquisitely sensitive to flow. Step increases of flow in the presence of ATP triggered large [Ca2+]i transients that slowly (60-150 s) returned to basal values. ATP-releasable [Ca2+]i was mobilized from intracellular stores, as well as obtained from the extracellular medium. Since potent ectonucleotidases on the cell surface are expected to influence local ATP concentrations, experiments were repeated using the poorly hydrolyzable ATP analogue beta, gamma-methyleneadenosine 5'-triphosphate (AMP-PCP). Comparison between ATP and AMP-PCP responses suggested that flow regulates the mass transport of agonist to the endothelial cell surface by overcoming the local effects of degradative enzymes. An additional, quite different phenomenon of flow-mediated [Ca2+]i regulation in endothelial cells was observed when [Ca2+]i oscillations induced by AMP-PCP in the absence of flow were shown to be reversibly inhibited by step increases in flow. These results imply that the effectiveness of local or systemic agonists in stimulating endothelial transduction will vary with flow rates. Regional variations in hemodynamic shear stresses associated with altered flow patterns throughout the arterial system are predicted to result in large variations of vessel wall responsiveness to physiological and pathological agonists.
L-propionylcarnitine increases postischemic blood flow but does not affect recovery of energy charge
Authors: Sassen L. M. , Bezstarosti K. , Van der Giessen W. J. , Lamers J. M. , Verdouw P. D.
Published: December 2017

Effects of pretreatment with L-propionylcarnitine (50 mg/kg, n = 9) or saline (n = 10) were studied in open-chest anesthetized pigs, in which ischemia was induced by decreasing left anterior descending coronary artery blood flow to 20% of baseline. After 60 min of ischemia, myocardium was reperfused for 2 h. In both groups, flow reduction abolished contractile function of the affected myocardium and caused similar decreases in ATP (by 55%) and energy charge [(ATP + 0.5ADP)/(ATP + ADP + AMP); decrease from 0.91 to 0.60], mean arterial blood pressure (by 10-24%), the maximum rate of rise in left ventricular pressure (by 26-32%), and cardiac output (by 20-30%). During reperfusion, “no-reflow” was attenuated by L-propionylcarnitine, because myocardial blood flow returned to 61 and 82% of baseline in the saline- and L-propionylcarnitine-treated animals, respectively. Cardiac output of the saline-treated animals further decreased (to 52% of baseline), and systemic vascular resistance increased from 46 +/- 3 to 61 +/- 9 mmHg.min.l-1, thereby maintaining arterial blood pressure. In L-propionylcarnitine-treated pigs, cardiac output remained at 75% of baseline, and systemic vascular resistance decreased from 42 +/- 3 to 38 +/- 4 mmHg.min.l-1. In both groups, energy charge but not the ATP level of the ischemic-reperfused myocardium tended to recover, whereas the creatine phosphate level showed significantly more recovery in saline-treated animals. We conclude that L-propionylcarnitine partially preserved vascular patency in ischemic-reperfused porcine myocardium but had no immediate effect on “myocardial stunning.” Potential markers for long-term recovery were not affected by L-propionylcarnitine.
Vagal reflexes and survival during acute myocardial ischemia in conscious dogs with healed myocardial infarction
Authors: De Ferrari G. M. , Vanoli E. , Stramba-Badiale M. , Hull S. S. , Foreman R. D. , Schwartz P. J.
Published: December 2017

The role of vagal tone and reflexes in the genesis of life-threatening arrhythmias was investigated in a clinically relevant animal model for sudden cardiac death. Forty-five dogs with a healed anterior myocardial infarction in which transient myocardial ischemia during exercise did not induce malignant arrhythmias were utilized for the study. They underwent a further exercise and ischemia test in which atropine (75 micrograms/kg) was injected before coronary artery occlusion. Novel occurrence of ventricular arrhythmia, or worsening of the type of arrhythmia present in the control test, occurred in 23 of 45 dogs (51%) and ventricular fibrillation occurred in 11 of 45 (24%, P = 0.001). Analysis of heart rate response to acute ischemia in the control test indicates that these 11 animals had powerful vagal reflexes during coronary artery occlusion, compared with the 34 survivors (-32 +/- 35 vs. +2 +/- 27 beats/min, P = 0.003). This study indicates that approximately 75% of animals resistant to ventricular fibrillation are characterized by weak sympathetic reflexes in response to acute myocardial ischemia. In the remaining 25% powerful vagal reflexes counteract concomitant reflex sympathetic hyperactivity, decrease heart rate, and are essential for survival.
Cromakalim and pinacidil dilate small mesenteric arteries but not small cerebral arteries
Authors: McCarron J. G. , Quayle J. M. , Halpern W. , Nelson M. T.
Published: December 2017

Small elevations in external K+ hyperpolarize and dilate small cerebral arteries. The hyperpolarization and dilation to K+ are blocked by barium (less than 0.1 mM). Since membrane hyperpolarization appears to be an important mechanism for dilation of these small cerebral arteries, we investigated the effects of the hyperpolarizing vasodilators, cromakalim and pinacidil, on isolated pressurized rat cerebral arteries (diameter of 158 +/- 5 microns at 50% of the systolic blood pressure). Cromakalim and pinacidil, which are potent relaxants of a variety of muscle types, were without effect on posterior cerebral arteries at concentrations that completely dilate similarly sized rat mesenteric arteries (diameter 134 +/- 6 microns at 50% of the systolic blood pressure). The mesenteric artery dilation to cromakalim and pinacidil was reversed by glibenclamide. However, unlike the cerebral arteries, mesenteric arteries did not exhibit a barium-sensitive dilation to external K+. Thus it appears that there may be differences in the types of K+ channels that are activated by dilating mechanisms in small cerebral and mesenteric arteries.
Effects of activated polymorphonuclear leukocytes on vascular smooth muscle tone
Authors: Mehta J. L. , Lawson D. L. , Nicolini F. A. , Ross M. H. , Player D. W.
Published: December 2017

Unstimulated polymorphonuclear leukocytes (PMNLs) release nitric oxide or a like material that relaxes vascular tissues. To determine the effects of activated PMNLs on vascular tone, precontracted rat aortic rings were exposed to ionophore A23187-treated PMNLs. Whereas "unstimulated" PMNLs caused 29 +/- 4% relaxation, "stimulated" PMNLs caused initial contraction followed by 90 +/- 7% relaxation of aortic rings. Indomethacin or the 5-lipoxygenase blocker piriprost had no effect on PMNL-induced initial contraction or subsequent relaxation. However, initial contraction was abolished and the subsequent vasorelaxation attenuated (22 +/- 5%) by the superoxide radical scavenger superoxide dismutase (SOD), suggesting that release of superoxide radicals may have induced vascular contraction and caused endothelial damage that would permit unopposed vasorelaxant effect of PMNLs. To examine this hypothesis, aortic rings were exposed to superoxide radicals (generated by xanthine plus xanthine oxidase, X + XO) or manually deendothelialized. These rings revealed marked relaxation (78 +/- 6 and 85 +/- 6%, respectively) in response to unstimulated PMNLs. These observations suggest that stimulated PMNLs exert an initial vasoconstrictor effect and a subsequent vasorelaxant effect in response to release of superoxide radicals and nitric oxide, respectively. Arachidonate metabolites or 5-lipoxygenase products do not appear to be important in the actions of PMNLs on vascular smooth muscle.
Effects of spatial dispersion of acetylcholine release on AV conduction responses to vagal stimulation in dogs
Authors: Yang T. N. , Cheng J. , Martin P. , Levy M. N.
Published: December 2017

We determined the effects on atrioventricular (AV) conduction of changing the spatial dispersion of acetylcholine (ACh) release from vagal nerve fibers in anesthetized dogs. We paced the atria at a constant rate and stimulated the vagus nerves with one stimulus burst per cardiac cycle. We varied the spatial heterogeneity of ACh release in the cardiac tissues by changing the stimulus voltage, and we varied the quantity of ACh release from each excited nerve fiber by changing the number of pulses per stimulus burst. We slightly changed the stimulus timing with each heartbeat to scan the entire cardiac cycle. We constructed phase-response curves (PRCs) by plotting the changes in AV conduction time as a function of the timing of vagal stimulation. We found that the amplitude of the PRC varied directly with average AV conduction time (AV), whereas the minimum-to-maximum phase difference of the PRC varied inversely with AV. However, for any given change in AV, the specific characteristics of the PRCs did not depend on whether we varied the number of pulses per burst or the stimulus voltage. Therefore, the phase-dependent characteristics of the dromotropic responses appear to be unaffected by the spatial dispersion of ACh release from the vagal nerve endings. The effects of vagal activity on the AV conduction time are determined by those conducting fibers that are the least restrained by neurally released ACh.
Effects of 12-HETE on isolated dog renal arcuate arteries
Authors: Ma Y. H. , Harder D. R. , Clark J. E. , Roman R. J.
Published: December 2017

12-Hydroxy-5,8,10,14-eicosatetraenoic acid (12-HETE) is one of the major noncyclooxygenase eicosanoids formed in vascular tissue. The vasoactive effects of the cytochrome P-450 product, 12(R)-HETE and the lipoxygenase product, 12(S)-HETE, on isolated, perfused renal arcuate arteries of the dog were investigated using videomicroscopy. R and S refer to stereoconfiguration of the hydroxy group at the twelfth position of this fatty acid structure. Cumulative doses of 12(R)-HETE produced a concentration-dependent vasoconstriction (n = 9) with a threshold dose of 10(-9) M. At a concentration of 3 x 10(-7) M, 12(R)-HETE reduced vascular diameter by 63 +/- 8 microns (from 306 +/- 17 microns), which was 37 +/- 6% of the maximal vasoconstrictor response to norepinephrine (10(-6) M). The effects of 12(R)-HETE were not altered by indomethacin (10(-6) M, n = 8). The vasoconstrictor response was associated with depolarization of vascular smooth muscle from -47 +/- 1 (15 cells) to -32 +/- 1 mV (12 cells). 12(S)-HETE was also a vasoconstrictor (n = 6), but the threshold concentration for vasoconstriction was 10(-8) M. Small renal arteries obtained from ischemic-injured, but not normal, kidneys produced a metabolite when incubated with arachidonic acid, which coeluted with a 12-HETE standard using reverse-phase high-pressure liquid chromatography. The rate of synthesis of this 12-HETE-like metabolite by renal arteries obtained from ischemic-injured and normal kidneys averaged 1.2 +/- 0.4 (n = 9) and 0.1 +/- 0.1 (n = 7) pmol.h-1.mg tissue-1, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)
Activation of brain adenosine receptors evokes vasodilation in skin arterioles
Authors: Proctor K. G. , Stojanov I. , Bealer S. L.
Published: December 2017

Metabolically stable adenosine (ADO) agonists were infused into cannulas chronically implanted in the lateral cerebral ventricle intracerebroventricularly (icv) while responses in skin microcirculation of pentobarbital-anesthetized hamsters were observed with intravital microscopy. Cyclohexyladenosine (CHA; A1-receptor selective; 0.0001-1 pmol) and N-ethylcarboxoamidoadenosine (NECA; A2-receptor selective; 0.01-0.05 pmol) were delivered in 10 microliters of bicarbonate-buffered Ringer vehicle. Mean systemic arterial blood pressure, heart rate, skin arteriolar diameter, and red blood cell velocity were continuously monitored. Blood flow was calculated from measurements of arteriolar diameter (20-40 microns) and red blood cell velocity. CHA icv caused dose-related decreases in blood pressure and heart rate, as well as increases in cutaneous perfusion. Comparable amounts of CHA administered intravenously evoked no response. Pretreatment with an A1-selective antagonist xanthine amine congener (XAC, 5 pmol icv or 1 mg/kg iv) had no effect on the depressor response but antagonized the bradycardia. In contrast, a nonselective antagonist 8-phenyltheophylline (8pTHEO, 5 pmol icv or 0.3 mg/kg iv) had no effect on the bradycardia but attenuated the depressor response. By either route, both antagonists prevented the cutaneous microcirculatory responses evoked by icv CHA. NECA icv produced hypotension but no change in the skin, and the depressor response was not altered by icv XAC. These observations provide direct evidence that chemical stimulation of central nervous system (CNS) ADO receptors is linked to a cutaneous vascular response that can be dissociated from other cardiorespiratory depressant actions of CNS ADO.
Whole body vascular capacitance response to vasopressin is mediated by autonomic function
Authors: Martin D. S. , McNeill J. R.
Published: December 2017

Effects of intravenous infusions of arginine vasopressin (AVP) on whole body vascular capacitance were determined in anesthetized cats when autonomic nervous system function was intact and, in other cats, when reflexes were blocked by the ganglionic blocking agent pentolinium. With the use of the constant cardiac output-reservoir technique, changes in reservoir volume were assumed to reflect reciprocal changes in whole body vascular capacitance. Relationships between the dose of AVP and the plasma concentration of the peptide achieved during infusions were not significantly different in the two groups of animals. Blood pressure responses to AVP were greater, whereas heart rate responses to the peptide were abolished in ganglion-blocked cats. In cats with intact autonomic function, reservoir volume decreased by 1.6, 4.2, and 7.8 ml/kg at AVP doses of 1, 10, and 100 ng.kg-1.min-1, respectively. In contrast, in ganglion-blocked cats, reservoir volume did not change significantly at 1.0 and 10 ng.kg-1.min-1 of AVP, and the highest dose caused a much smaller change in volume (3 ml/kg) than that observed in cats with intact autonomic function (7.8 ml/kg). Systemic compliance was unchanged by AVP in both groups of animals, suggesting that the increases in whole body vascular capacitance were likely due to changes in unstressed volume. The results suggest that reflexively mediated changes in autonomic function increase whole body vascular capacitance during elevations in the circulating levels of AVP to plasma concentrations that are biologically relevant. These findings may explain how AVP decreases cardiac output in animals with an intact autonomic nervous system.
Modulation by extracellular pH of bradykinin-evoked activation of Ca(2+)-activated K+ channels in endothelial cells
Authors: Thuringer D. , Diarra A. , Sauve R.
Published: December 2017

We used the patch-clamp technique to investigate, via the activation of Ca(2+)-activated potassium channels [K(Ca2+)channels], the effects of extracellular pH (pHo) on the bradykinin (BK)-stimulated rise in cytosolic Ca2+ concentration in bovine aortic endothelial cells (BAE). In cell-attached experiments, the external application of BK caused a transient activation of the K(Ca2+) channels. Increasing pHo from 7.3 to 9 maintained the channel activity, which was not inhibited by withdrawing the agonist. The channel-activation process could be blocked either by removing external Ca2+ or by depolarizing the cells with a high-K+ external solution. These results indicate that the Ca2+ influx triggered by BK contributes in maintaining the agonist-evoked response in high pHo. Changes in pHo produced a slight increase in the intracellular pH (pHi) measured fluorimetrically with the H+ indicator dye 2',7-bis(carboxyethyl)5(6')-carboxyfluorescein. However, increasing pHi by the external application of NH4Cl at physiological pHo caused a rapid decline and not an increase in the K(Ca2+) channel activity triggered by BK. In fura-2-loaded cells, alkaline pHo had no effect on the time course of the Ca2+ response to BK in external Ca(2+)-free conditions, suggesting that the Ca2+ extrusion process is not affected by pHo. Our results suggest that the BK-evoked Ca2+ influx, which is required to reload internal Ca2+ stores, is controlled by a mechanism depending on extracellular H+.
Activation of cardiac ATP-sensitive K+ current during hypoxia: correlation with tissue ATP levels
Authors: Deutsch N. , Klitzner T. S. , Lamp S. T. , Weiss J. N.
Published: December 2017

Although previous work has implicated activation of ATP-sensitive K+ currents (IK,ATP) in action potential duration (APD) shortening and increased cellular K+ efflux during hypoxia, ischemia, and metabolic inhibition, no prior study has directly assessed the tissue levels of ATP at which IK,ATP activates in intact cardiac muscle. Accordingly, we correlated changes in tissue high-energy phosphate levels during substrate-free hypoxia with activation of IK,ATP in intact voltage-clamped rabbit papillary muscles. During 10 min of hypoxia, the outward K+ current measured in response to a voltage-clamp pulse step from -50 to 0 mV increased from 8.57 +/- 0.27 to 15.67 +/- 1.41 microA (P less than 0.05, n = 6), and APD decreased from 452 +/- 54 to 292 +/- 56 ms (P less than 0.05, n = 6). Glibenclamide (10 microM), a specific IK,ATP blocker, prevented both of these changes. In a parallel set of experiments, papillary muscles were freeze-clamped and assayed for tissue ATP. In these muscles, 10 min of hypoxia resulted in a comparable degree of APD shortening (441 +/- 24 to 297 +/- 18 ms, P less than 0.05, n = 12), and tissue ATP levels fell from 13.2 +/- 1.3 to 9.7 +/- 0.7 mumol/g dry wt (P less than 0.05, n = 12). These results directly demonstrate that IK,ATP is activated and causes APD shortening during hypoxia in intact cardiac muscle despite only a modest (approximately 25%) decline in tissue ATP content.
Decreased flow reserve in "stunned" myocardium after a 10-min coronary occlusion
Authors: Triana J. F. , Bolli R.
Published: December 2017

The effect of brief reversible ischemia on coronary vascular function remains controversial. Studies using a 15-min coronary occlusion have reported an impairment of vasodilator reserve, whereas studies using shorter occlusions have not. To elucidate the relation between postischemic vascular abnormalities and duration of ischemic insult, we evaluated coronary reserve after a 10-min coronary occlusion in the same model previously used for a 15-min occlusion. Open-chest dogs (n = 12) underwent a 10-min left anterior descending coronary artery occlusion followed by reflow. Four hours after reperfusion, coronary resistance was higher in the postischemic “stunned” myocardium than in the nonischemic myocardium, both at rest and during adenosine-induced maximal vasodilation; in addition, all indexes of reactive hyperemia after a 40-s coronary occlusion were significantly lower than at baseline. There was no appreciable correlation between systolic wall thickening in the stunned myocardium and 1) the resting myocardial perfusion, 2) the hyperemia attained during adenosine, and 3) the hyperemic response to a 40-s coronary occlusion. The loss of coronary reserve was less than that previously observed after a 15-min occlusion, suggesting that the magnitude of the postischemic vascular abnormalities increases with the duration of the ischemic insult. In control dogs (n = 8), there was no change in coronary reserve. We conclude that a brief ischemic insult lasting only 10 min is sufficient to cause a prolonged increase in resting vascular resistance and a prolonged impairment in vasodilator responsiveness, both of which persist for at least 4 h, indicating the presence of a postischemic microvascular dysfunction. The severity of these vascular derangements is not related to the severity of the contractile depression, suggesting that they may represent a relatively independent phenomenon. The differences among previous studies may be due, in part, to the fact that the abnormalities observed after a 10-min occlusion are relatively subtle.
Influence of histaminergic receptors on denervated canine gracilis muscle vascular tone during endotoxemia
Authors: Bond R. F. , Vildibill H. D. , Krech L. H. , Hershey J. C.
Published: December 2017

The purpose of this study was to determine if endogenously released histamine and its non-neural interaction with the H1- and H2-histaminergic receptors in the peripheral vasculature can account for the decompensatory loss of peripheral vascular tone associated with the hypotension occurring during endotoxemia. A denervated in situ constant flow double canine gracilis muscle preparation that permitted one muscle to serve as a control (GMc) for the contralateral experimental muscle (GMe) was used. Endotoxemia was induced by intravenous infusion of 2 mg.kg-1.30 min-1 endotoxin. The specific H1 and H2 antagonists diphen-hydramine and cimetidine were infused either together or separately in both high and low dosages into the GMe. Blockades were validated by intra-arterial injection of histamine or the specific agonists betahistine for H1 and dimaprit for H2 receptors. The results suggest that the high-dose diphenhydramine produced a nonspecific dilation not seen with the lower dose. Because both the blocked and unblocked vascular beds exhibited the same degree of vasodilation after endotoxin, these studies do not support the hypothesis that endogenously released histamine is responsible for the loss of vascular tone. These studies do verify, however, that a nonneurally mediated loss of skeletal muscle vascular tone is an important factor to consider in the overall cardiovascular hypotension occurring during endotoxin shock.
Measurement of blood flow in rat eyes by hydrogen clearance
Authors: Yu D. Y. , Alder V. A. , Cringle S. J.
Published: December 2017

Intraocular measurements of blood flow have been made in the rat eye using hydrogen-clearance polarography. Hydrogen was delivered by a bolus injection of hydrogen-saturated saline via a cannula in the lingual artery of the anesthetized rat. An intraocularly placed hydrogen-sensitive microelectrode monitored the arrival and clearance of hydrogen preretinally adjacent to retinal arteries, veins, and intervascular areas. The effect of stepwise penetration through the retina and into the choroid was also determined, and a map of hydrogen distribution in the retina during hydrogen delivery and clearance was produced. Intraocular measurements, which have the advantage that the electrode location can be clearly visualized, together with computer control of the bolus injection and data collection, have allowed highly repeatable measurements of local blood flow to be made. The mean blood flow in retinal tissue was 373 +/- 51 ml.min-1.100 g-1 (values are means +/- SD, n = 32). The correlation between the nature of the hydrogen clearance curve and the location of the electrode helps explain data from other studies in which the position of the electrode with respect to the vasculature was unknown.
Control of cardiac energy turnover by cytoplasmic phosphates: 31P-NMR study
Authors: Kupriyanov V. V. , Lakomkin V. L. , Korchazhkina O. V. , Steinschneider A. Ya. , Kapelko V. I. , Saks V. A.
Published: December 2017

Energy flux, estimated from the cardiac work index (pressure-rate product) and the rate of oxygen consumption, was varied in different ways; and the free concentrations of cytosolic phosphates were detected by the 31P-nuclear magnetic resonance method. A reversible decrease in phosphocreatine (PCr) and concomitant increase in [ADP] at nearly constant Pi were induced by 2-deoxyglucose (2-DG) treatment and its subsequent washout and were followed by a reversible suppression of pressure-rate product and elevation of end-diastolic pressure. 2-DG treatment also resulted in an irreversible and severe reduction of the cytosolic adenine nucleotide pool (to approximately one-third of control value) that did not recover during 2-DG washout. Reduction of the energy turnover rate, either by suppression of the PCr shuttle with iodoacetamide or by inhibition of the respiratory chain with amytal, was associated with a drop of PCr level, an elevation of both [ADP] and [Pi], and a rise of end-diastolic pressure. In contrast, a decrease in energy flux by reduction of perfusate Ca2+ led to a PCr rise and a fall in [ADP] and [Pi]. Most of these experimental groups were exposed to two types of loads, isoproterenol stimulation and coronary flow (CF) elevation. Iodoacetamide-treated hearts showed a poor mechanical response to both types of loads compared with other groups. The metabolic response to isoproterenol was uniform in all groups and was associated with some decrease in PCr and increase of [ADP] and [Pi], implying limitations in the respiratory chain. In contrast, activation of energy flux by a CF rise in control and amytal-inhibited hearts did not affect the concentrations of PCr, ADP, and Pi. Thus cytosolic phosphates can serve as a feedback signal for energy production and utilization when the single control point is located in oxidative phosphorylation pathway or contractile system. If control of energy metabolism is equally distributed among producing and utilizing systems (CF variation), other regulatory mechanisms seem to be involved, e.g., cytosolic [Ca2+].

contraction-relaxation; creatine kinase; cytosolic phosphates; isolated rat heart; oxygen consumption
Effect of work on intracellular calcium of the intact heart
Authors: Fralix Teresa A. , Heineman Frederick W. , Balaban Robert S.
Published: December 2017

Intracellular calcium has been proposed to play a key role in the orchestration of metabolic rate with contractile activity in the mammalian heart. Calcium is believed to accomplish this task by modulating the contractile apparatus as well as the metabolic process directly, and perhaps simultaneously, during alterations in cardiac work. The purpose of this study was to evaluate whether appropriate changes in intracellular calcium accompany alterations in cardiac work in the intact working rabbit heart. A range of myocardial oxygen consumption was obtained from 0.94 to 6.51 μmol·g LV wt-1·min-1 by changing afterload or -agonist addition. With the increase in work and associated increase in respiration, an increase in intracellular calcium was observed, on the basis of indo-1 fluorescence. These results indicate that intracellular calcium is a valid candidate as a cytosolic transducer contributing to the orchestration of myofibril adenosinetriphosphatase activity and oxidative phosphorylation in the intact heart.

oxygen consumption; indo-1; fluorescence; rabbit; afterload; isoproterenol
Cellular adaptation during chronic neonatal hypoxic pulmonary hypertension
Authors: Stenmark Kurt R. , Aldashev Almas A. , Orton Ernest C. , Durmowicz A. G. , Badesch D. B. , Parks W. C. , Mecham R. P. , Voelkel N. F. , Reeves J. T.
Published: December 2017

Newborn animals develop more severe hypoxic pulmonary hypertension than do adults, their vascular changes are greater, and both the hypertension and vascular changes occur more rapidly. We hypothesize that this differential developmentally controlled response may arise from either a difference in the type or quantity of endogenously secreted mediators in response to a given injury or a difference in the replicative and/or matrix-producing response of the vascular cells to physical or chemical stimuli. We investigated the effect of chronic hypoxia (14 days) on the proliferative and matrix-producing phenotype of the neonatal (14-day-old) pulmonary artery smooth muscle cell (SMC) and examined the heterogeneity and potential mechanisms responsible for this response. In situ hybridization studies demonstrated a remarkable change in the distribution of cells hybridizing with a tropoelastin cRNA probe after 14 days of hypoxia. Studies also demonstrated a population of SMC that did not hybridize with the elastin or collagen probes, indicating that the pulmonary artery contains SMC of multiple phenotypes and that the response to hypoxic and hemodynamic stress is not uniform for the various types. Bromodeoxyuridine labeling experiments indicated a large increase in DNA synthesis in hypertensive vessels, which, again, was not uniform either across or along the arterial wall. In vitro experiments with neonatal SMC suggested that hypoxia alone could not be responsible for the proliferative or matrix changes. These observations were supported by in vivo experiments in which coarctation of the left pulmonary artery, which markedly decreased pressure and flow to the left lung in hypoxic animals (14 days), resulted in significant decreases in collagen and elastin message levels in the left pulmonary artery distal to the coarctation compared with location-matched vessels from the right lung. Finally, we noted marked decreases in B-receptor density and adenyl cyclase activity in right atrial and pulmonary artery tissue from the chronically hypoxic animals. Decreases in the ability of the cell to produce adenosine 3',5'-cyclic monophosphate could significantly affect both the proliferative and matrix-producing potential of the SMC. We conclude that in vivo adaptation of the pulmonary artery SMC to chronic hypoxia includes changes in protein synthesis, cell proliferation, receptor expression, and enzyme activity. Further, there is a marked heterogeneity of these responses both across and along the arterial wall.,

hypoxia; phenotype; signal transductions; smooth muscle cells
Superoxide dismutase recovers altered endothelium-dependent relaxation in diabetic rat aorta
Authors: Hattori Y. , Kawasaki H. , Abe K. , Kanno M.
Published: December 2017

Experiments were designed to characterize endothelium-dependent relaxation in thoracic aortic rings obtained from streptozotocin-induced diabetic rats. When the degree of the peak relaxation was compared, the endothelium-dependent relaxant responses to acetylcholine, histamine, or ADP in precontracted aortic rings showed that there was no significant difference between diabetic and control vessels. However, the time courses appeared quite different. The endothelium-dependent relaxant responses in diabetic vessels were more transient than those in control vessels. In addition, the rapid fade of the endothelium-dependent responses observed in diabetic vessels was significantly suppressed by pretreatment with superoxide dismutase. Pretreatment with catalase, deferoxamine, allopurinol, or indomethacin did not prevent the rapid fade of the endothelium-dependent relaxation. The endothelium-independent relaxation induced by nitric oxide also faded more quickly in diabetic vessels; this impairment was less pronounced in the presence of superoxide dismutase. These results suggest that the transient nature of the endothelium-dependent relaxation is more marked in diabetic rat aorta as a result of an enhanced accumulation of superoxide anion.
Tone, autoregulatory properties, and wall thickness-to-radius ratio in skeletal muscle arterioles
Authors: Kostromina E. Y. , Rodionov I. M. , Shinkarenko V. S.
Published: December 2017

Internal diameter, wall thickness, wall thickness-to-radius ratio (W/r), and blood flow velocity in arterioles of different branching orders were measured in the rat cremaster muscle. The heterogeneity of W/r increased in more distal orders. During papaverine treatment, there was a direct correlation between vasodilation and W/r. When pressure was decreased by 20%, 42% of arterioles showed autoregulation; the remaining arterioles constricted in proportion to initial W/r. Similarly, the dilatation of arterioles with autoregulatory properties increased with initial W/r. It is concluded that W/r is an important parameter quantitatively related to tone, mechanical characteristics, and autoregulatory properties of arterioles.
Cerebral oxidative metabolism and redox state during hypoxia-ischemia and early recovery in immature rats
Authors: Yager J. Y. , Brucklacher R. M. , Vannucci R. C.
Published: December 2017

Intracellular pH (pHi) and cytoplasmic and mitochondrial oxidation-reduction (redox) states of cerebral tissue were examined in relation to perturbations of glycolytic and tricarboxylic acid cycle intermediates and of high-energy phosphate reserves during hypoxia-ischemia and the early recovery period in the immature rat. Seven-day postnatal rats underwent unilateral common carotid artery ligation and exposure to 8% O2 for 3 h, after which they were quick frozen in liquid N2 at the terminus of hypoxia-ischemia and at 10, 30, 60, and 240 min of recovery for enzymatic fluorometric analysis of cerebral metabolites. During hypoxia-ischemia, concentrations of glucose and alpha-ketoglutarate in the cerebral hemisphere ipsilateral to the carotid artery occlusion were depleted to 10 and 70% of control, respectively; pyruvate was unchanged. During recovery, glucose, pyruvate, and alpha-ketoglutarate increased above their respective control values. Calculated pHi decreased from 7.0 (control) to 6.6 during hypoxia-ischemia and normalized by 10 min of recovery. The cytoplasmic NAD+/NADH ratio decreased (increased reduction) to 50% of control during hypoxia-ischemia and remained in the reduced state throughout 4 h of recovery. Paradoxically, mitochondrial NAD+/NADH was oxidized at the terminus of hypoxia-ischemia. The mitochondrial oxidation which developed during hypoxia-ischemia presumably results from a limitation of cellular substrate (glucose) supply, which in turn leads to a depletion of high-energy phosphate reserves, culminating in brain damage.
31P-NMR studies of isolated adult heart cells: effect of myoglobin inactivation
Authors: Gupta R. K. , Wittenberg B. A.
Published: December 2017

31P nuclear magnetic resonance (NMR) studies of isolated adult rat heart cells revealed that the cells maintained high-energy phosphates for up to 6 h in polyamide hollow fibers perfused with well-oxygenated nutrient medium. Glucose plus pyruvate superfused heart cells maintained [phosphocreatine]/[ATP] at 1.4 +/- 0.1, internal pH at 7.09 +/- 0.04 (external pH = 7.25), and intracellular free Mg2+ at 0.51 +/- 0.04 mM. In glucose-containing media, hypoxia was accompanied by a reversible decrease in intracellular ATP and phosphocreatine of approximately 50% and 80%, respectively, while the intracellular free Mg2+ was reversibly increased by 40%. However, inhibition of glycolysis by iodoacetate in aerobic pyruvate-containing medium did not significantly alter high-energy phosphate content. Inactivation of intracellular myoglobin with 1-2 mM sodium nitrite, which reduces the steady-state respiratory oxygen consumption rate by 30%, caused a significant (30%) decrease in intracellular phosphocreatine peak, which was reversed upon removal of sodium nitrite. The nitrite-induced decrease in phosphocreatine was also observed in iodoacetate-treated myocytes but not in oligomycin-treated cells. These results indicate that functional myoglobin enhances high-energy phosphate synthesis in well-oxygenated myocytes.
Phospholamban mediates the beta-adrenergic-enhanced Ca2+ uptake in mammalian ventricular myocytes
Authors: Sham J. S. , Jones L. R. , Morad M.
Published: December 2017

To probe the molecular mechanism responsible for the relaxant effect of catecholamines in heart muscle, we studied the effect of a monoclonal antibody (2D12) against phospholamban in intact whole cell clamped guinea pig ventricular myocytes, in which intracellular Ca2+ transient and Ca2+ current were simultaneously measured. The antibody stimulated Ca2+ uptake in guinea pig ventricular sarcoplasmic reticular vesicles, shifting the apparent dissociation constant for activation by Ca2+ from 200 to 60 nM. The stimulatory effect of the antibody could be mimicked by the catalytic subunit of adenosine 3',5'-cyclic monophosphate-dependent kinase and could be blocked by phospholamban peptide 2-25. Dialysis of ventricular myocytes with the antibody enhanced the rate of uptake of Ca2+ and significantly suppressed the ability of isoproterenol to enhance the rate of uptake and release of Ca2+ by depolarizing pulses. These data suggest that not only is phosphorylation of phospholamban crucial in sequestration of Ca2+ by the sarcoplasmic reticulum, but that this process may account for the catecholamine-enhanced rate of Ca2+ uptake release in heart muscle.
Expression and cellular distribution of heat-shock and nuclear oncogene proteins in rat hearts
Authors: Snoeckx L. H. , Contard F. , Samuel J. L. , Marotte F. , Rappaport L.
Published: December 2017

An early, transient accumulation of mRNAs of the protooncogenes c-fos and c-myc and the heat-shock protein HSP70 has been described in hypertrophying rat hearts. It is unclear 1) in which cardiac cell type-these gene activations occur and 2) whether the corresponding proteins are translated. We studied protein expression in rat hearts during ontogenic development and under stress conditions associated with pressure overload with the use of immunofluorescent techniques. During cardiac development no HSP70 could be detected. c-Fos was expressed consistently after birth but only in coronary smooth muscle cells, and c-Myc was found exclusively in adult coronary endothelium and myocardial nonmuscle cells. In adult rats, HSP70 and, to a lesser extent, c-Fos were induced in myocardial muscle and some nonmuscle cells within 3 h following methohexital sodium anesthesia. A similar, more intense immunolabeling of these peptides was observed after thoracotomy and/or aortic stenosis. The coronary c-Fos and c-Myc labeling remained unchanged in these conditions. Thus the expression in cardiac muscle and nonmuscle cells of the three peptides differs and depends on different triggers.