bluuebunny/crossref_metadata_2025 huggingface dataset:
Suction effusion fluid from skin and constituent analysis: new candidate for interstitial fluid
Authors: Kayashima S. , Arai T. , Kikuchi M. , Nagata N. , Ito N. , Kuriyama T. , Kimura J.
Published: December 2017

The authors analyzed the constituents of effuse transcutaneous fluid, labeled suction effusion fluid (SEF), and monitored its glucose concentration during glucose loading in rabbits (Japan White, female) under pentobarbital anesthesia. The SEF was sampled by suctioning corneal layer-stripped skin at 400 mmHg absolute pressure. The SEF proved to have nearly the same concentrations as serum for lower-molecular-weight substances such as glucose, creatinine, and urea nitrogens, but not for higher-molecular-weight substances such as serum proteins. The SEF protein concentration was one-fourth that of serum protein. Proteins > 100 kDa molecular mass were barely detectable in the SEF. Monitoring of SEF glucose change every 10 min during intravenous glucose loading was successfully accomplished, and SEF glucose concentration followed blood glucose concentration with a 10-min delay. The SEF was thought to consist of interstitial fluid and/or effuse fluid from small vessels in subcutaneous tissue.
Myocardial and endothelial dysfunction after multiple, brief coronary occlusions: role of oxygen radicals
Authors: Gross G. J. , O'Rourke S. T. , Pelc L. R. , Warltier D. C.
Published: December 2017

The major objective of the present study was to determine the effect of multiple, brief periods of coronary artery occlusion and reperfusion on postischemic contractile function (sonomicrometry) and endothelium-dependent vasodilator responses in isolated conduit coronary artery rings obtained from anesthetized dogs. The role of oxygen-derived free radicals was also investigated. Dogs were subjected to four 5-min episodes of left anterior descending coronary occlusion interspersed with 5 min of reperfusion followed by a final 60-min reperfusion period. The multiple occlusion-reperfusion protocol resulted in regional segment dysfunction (37 +/- 15% of preocclusion values at 60 min of reperfusion) and attenuated endothelium-dependent responses to acetylcholine, bradykinin, and the calcium ionophore, A23187. Responses to the endothelium-independent vasodilator, sodium nitroprusside, were unaffected. Infusion of superoxide dismutase (5,000 U/kg) and catalase (55,000 U/kg) markedly improved the recovery of myocardial function at 30 and 60 min of reperfusion and completely protected against vascular endothelial damage. These results suggest an important role for oxygen-derived free radicals in the myocardial and endothelial injury that occurs in this model of multiple stunned myocardium.
Baroreflex control of regional capacitance and blood flow distribution with or without alpha-adrenergic blockade
Authors: Deschamps A. , Magder S.
Published: December 2017

Regional blood volumes (Vb), unstressed volumes (V0), blood flow distribution, venous compliances (Cv), venous resistances (Rv), and time constants of drainage (tau v) were determined in dogs anesthetized with alpha-chloralose at carotid sinus pressures (Pcs) of 50 and 200 mmHg and dosed with alpha-adrenergic or ganglionic blockade at a Pcs of 50 mmHg. Vb was measured in each region from indicator dilution curves and mean transit times. V0 was extrapolated from the pressure-volume curves. Pcs of 50 and 200 mmHg were maintained in random order. With a decrease in Pcs, arterial pressure increased from 58.7 +/- 4.1 to 104.6 +/- 6.4 mmHg (P < 0.01), peripheral fractional blood flow decreased from 69.8 +/- 3.8 to 55.8 +/- 3.9% (P < 0.001), splanchnic Vb decreased from 28.3 +/- 1.9 to 19.3 +/- 1.2 ml/kg (P < 0.01), and splanchnic V0 decreased from 19.6 +/- 1.4 to 6.3 +/- 2.1 ml/kg (P < 0.001). Splanchnic Rv and tau v also decreased, whereas splanchnic Cv increased. Phentolamine at low Pcs only partially reversed the decrease in splanchnic capacitance, whereas hexamethonium completely abolished it. In conclusion, changes in splanchnic Rv and blood flow distribution are important components of the carotid sinus reflex, and alpha-adrenergic receptor activation is only partially responsible for the changes in vascular capacitance by the baroreceptor reflex.
Microvascular ischemia-reperfusion injury in striated muscle: significance of "no reflow"
Authors: Menger M. D. , Steiner D. , Messmer K.
Published: December 2017

“No reflow” has been implicated as prominent phenomenon in microvascular injury associated with ischemia-reperfusion (I/R). The objectives of this study were 1) to elucidate the significance of no reflow in microvascular I/R injury of striated muscle and 2) to determine whether reactive oxygen metabolites play a role in the development of postischemic no reflow. By use of the hamster dorsal skinfold preparation and intravital microscopy, microvascular perfusion of capillaries and postcapillary venules of striated muscle was quantitatively assessed before and 30 min, 2 h, and 24 h after 4 h of tourniquet-induced ischemia. I/R was characterized by a significant reduction (P < 0.01) in functional capillary density to 35% of baseline values during initial reperfusion, with incomplete recovery after 24 h (n = 9). In addition, capillary perfusion was found to be extremely heterogeneous, and wall shear rate in postcapillary venules was significantly decreased (P < 0.01). Treatment with either superoxide dismutase (SOD; n = 9) or allopurinol (n = 9) resulted in maintenance of capillary density of 60% of baseline (P < 0.05). Furthermore, I/R-induced capillary perfusion inhomogeneities and decrease of wall shear rate in venules were attenuated significantly (P < 0.01) by SOD and allopurinol. Thus part of capillary perfusion disturbances during I/R in striated muscle may be caused by increased postcapillary vascular resistance, probably mediated by reactive oxygen metabolites. However, the fact that in SOD- and allopurinol-treated animals 40% of the capillaries were still found to be nonperfused indicates that mechanisms other than oxygen radicals play an important role in the development of postischemic no reflow.
Prostacyclin-induced vasodilation in rabbit heart is mediated by ATP-sensitive potassium channels
Authors: Jackson W. F. , Konig A. , Dambacher T. , Busse R.
Published: December 2017

We tested the hypothesis that prostacyclin and its stable analogue iloprost act as agonists of ATP-sensitive potassium channels (KATP) to induce vasodilation of the coronary circulation. The selective blocker of KATP, glibenclamide, was used as a probe for vasodilation mediated by KATP in saline-perfused rabbit hearts (constant flow, Langendorff preparation). Glibenclamide (10-300 nM) significantly increased coronary perfusion pressure and inhibited vasodilation induced by iloprost (1-30 nM), prostacyclin (10 nM), adenosine (0.3 microM), and cromakalim (0.1 microM), a known agonist of KATP. This potassium channel antagonist also inhibited vasodilation of rabbit hearts in response to 10 nM bradykinin in the presence of an inhibitor of nitric oxide synthase (30 microM NG-nitro-L-arginine). Because bradykinin-induced vasodilation is mediated by prostacyclin released from endothelial cells when nitric oxide synthesis is inhibited, these data indicate that glibenclamide is also effective against endogenous prostacyclin. The inhibitory effects of glibenclamide were selective: vasodilation induced by sodium nitroprusside (1-10 microM) or acetylcholine (1 microM) were not inhibited by this potassium channel antagonist. In addition, basal and bradykinin-stimulated release of 6-ketoprostaglandin F1 alpha was not affected by this antagonist of KATP. Glibenclamide also did not inhibit the activation of adenylate cyclase, as indicated by its lack of effect on adenosine 3',5'-cyclic monophosphate accumulation induced by iloprost (10 nM-1 microM) in bovine coronary arterial segments, a tissue in which iloprost-induced vascular smooth muscle relaxation is inhibited by glibenclamide.(ABSTRACT TRUNCATED AT 250 WORDS)
Nitric oxide and cGMP: mediators of pelvic nerve-stimulated erection in dogs
Authors: Trigo-Rocha F. , Aronson W. J. , Hohenfellner M. , Ignarro L. J. , Rajfer J. , Lue T. F.
Published: December 2017

We sought to determine whether the L-arginine-nitric oxide-guanosine 3',5'-cyclic monophosphate (cGMP) pathway, known to mediate neurostimulation-induced smooth muscle relaxation in penile tissue of rabbits and humans in vitro, is operative also in vivo. Adult male dogs (n = 9) were subjected to direct electrical stimulation of the pelvic nerves to induce penile tumescence. Intracavernous injection of the nitric oxide-releasing substance S-nitroso-N-acetylpenicillamine resulted in similar tumescence. Intracavernous injection of a specific inhibitor of nitric oxide synthesis, NG-nitro-L-arginine, blocked pelvic nerve-stimulated tumescence, and this was partially reversed by intracavernous injection of the nitric oxide precursor L-arginine. Furthermore, neurostimulated tumescence was inhibited by methylene blue, an inhibitor of cytosolic guanylate cyclase and enhanced by M&B 22948, a cGMP phosphodiesterase inhibitor. These in vivo findings support the hypothesis that cavernous smooth muscle relaxation and penile tumescence are mediated by nitric oxide and cGMP.
Single delayed rectifier potassium channels from rabbit coronary artery myocytes
Authors: Volk K. A. , Shibata E. F.
Published: December 2017

Cell-attached patches from rabbit coronary artery single smooth muscle cells contained two distinct potassium channel types, namely a large conductance calcium-activated potassium channel and a smaller voltage-activated potassium channel representing the delayed rectifier (IK). When a physiological potassium ion gradient was used, the average slope conductance of single IK channels was 7.26 pS. The time course of activation measured from ensemble averages was well fit by a single exponential raised to the power of 2 and was voltage dependent. Experiments were then performed with potassium (140 mM) on both sides of the membrane to resolve single IK channel currents during deactivation. Ensemble averages of this activity were well described by a two-component exponential, and the time constants were voltage dependent. Mean open times were significantly shorter during deactivation than during activation. Closed time distributions typically had two components. These kinetic characteristics were used in testing various state models for voltage-dependent potassium channels.
Increased alpha 1-adrenergic vascular sensitivity during development of hypertension in conscious dogs
Authors: Uemura N. , Vatner D. E. , Shen Y. T. , Wang J. , Vatner S. F.
Published: December 2017

The goal of this study was to determine whether enhanced vascular responsiveness during the development of perinephritic hypertension is selective or nonspecific. The effects of graded infusions of norepinephrine (NE), phenylephrine (PE), angiotensin II (ANG II), and vasopressin (VP) were examined on mean arterial pressure, total peripheral resistance (TPR), and aortic pressure-diameter relationships in conscious dogs. NE increased TPR significantly greater (P < 0.01) in hypertension than normotension, as did PE infusion, whereas ANG II and VP increased TPR similarly before and after hypertension. Analysis of aortic pressure-diameter relationships also demonstrated significant (P < 0.05) shifts in response to NE and PE, but not ANG II and VP, during the development of hypertension. In normotensive dogs, low doses of ANG II infusion also enhanced the vasoconstrictor response not only to NE and PE but also to VP. In contrast to what was observed in hypertension, in the presence of ANG II infusion after ganglionic blockade, enhanced responses to PE and NE were no longer observed. The alpha 1-adrenergic receptor density in membrane preparations from aortic tissue, as determined by [3H]prazosin binding, was higher (P < 0.05) in hypertensive dogs than control dogs. Thus the vascular responsiveness in the aorta and resistance vessels is enhanced to alpha 1-adrenergic stimulation, but not to all vasoconstrictors, during developing perinephritic hypertension. The mechanism appears to involve increased alpha 1-adrenergic receptor density.
Dynamics of intracellular free Mg2+ changes in a vascular smooth muscle cell line
Authors: Quamme G. A. , Dai L. J. , Rabkin S. W.
Published: December 2017

Intracellular free Mg2+ concentration ([Mg2+]i) has been implicated in the pathogenesis of hypertension. It has been postulated that Mg2+ through its antagonistic effects on intracellular Ca2+ concentration may affect tension and contractility of vascular smooth muscle cells. An established cell line of rat thoracic aorta cells (A10) was cultured on glass cover slips, and [Mg2+]i was determined by fluorescent techniques on single cells with the use of mag-fura-2. Basal [Mg2+]i was 0.52 +/- 0.02 mM (n = 15). Vascular smooth muscle cells were challenged with A23187 plus 5 mM MgCl2 to rapidly elevate [Mg2+]i. [Mg2+]i increased to a peak of 1.03 +/- 0.09 mM within 1-2 s and then quickly declined to below basal levels, 0.30 +/- 0.03 mM, within 45-60 s despite the continued presence of A23187 and external Mg2+. The rapid removal of the Mg2+ challenge to below basal levels suggests the presence of intracellular transport mechanisms, likely in intracellular compartments or organelles. Spatial imaging studies indicated that Mg2+ is heterogeneously distributed within the cell with the greatest variations in the perinuclear region, the area of most cytosolic organelles. Vanadate, an inhibitor of P-type adenosinetriphosphatases, inhibited the removal rate from 10.2 +/- 0.9 to 6.8 +/- 1.0 microM/s. Inhibitors of intracellular Ca2+ mobilization, thapsigargin, dantrolene, and 3,4,5-trimethoxybenzoic acid 8-(diethylamino)octyl ester, inhibited Mg2+ sequestration. Ryanodine and caffeine had no effect on Mg2+ removal. Ruthenium red did not inhibit Mg2+ sequestration, but oligomycin B slowed its removal. These studies demonstrated that [Mg2+]i in vascular smooth muscle cells is carefully controlled by active mechanisms involving intracellular and plasma membrane transporters.(ABSTRACT TRUNCATED AT 250 WORDS)
Dependence of cardiac filling pressure on cardiac output during rest and dynamic exercise in dogs
Authors: Sheriff D. D. , Zhou X. P. , Scher A. M. , Rowell L. B.
Published: December 2017

At rest, central venous pressure (CVP) falls when cardiac output (CO) rises. This can be attributed to flow-dependent redistribution of blood volume from central to peripheral blood vessels. In contrast, CVP rises during dynamic exercise despite a rise in CO. Therefore peripheral circulatory changes during exercise must counteract the factors that lower CVP when CO rises during rest. Our objectives were to determine the importance of blood flow, the muscle pump, and reflexes on changes in ventricular filling pressure during dynamic exercise. In seven dogs with a surgically produced atrioventricular (AV) block, normal relationships between CO and CVP were established by AV-linked pacing (normal heart rates) during rest and exercise. Cardiac output was altered during rest and treadmill exercise (4 miles/h at 0, 10, or 20% grade) by changing ventricular pacing rate to establish curves relating delta CVP to delta CO. These curves were displaced rightward (higher CO) and upward (higher CVP) by exercise because of the muscle pump. Changing CO by pacing during rest and exercise revealed a constant slope for delta CVP/delta CO of -2.7 mmHg.l-1.min-1. Blockade of reflex vasoconstriction and venoconstriction with hexamethonium at rest and during mild exercise (to isolate effects of the muscle pump) did not alter these slopes or the displacement of the curves by exercise, although CVP was 4.3 mmHg lower at a given CO after blockade.(ABSTRACT TRUNCATED AT 250 WORDS)
Dietary sodium stimulates ouabainlike activity in adrenalectomized spontaneously hypertensive rats
Authors: Leenen F. H. , Harmsen E. , Yu H. , Yuan B.
Published: December 2017

Both the adrenal glands and the hypothalamus have been proposed to produce compound(s) with ouabainlike activity (OLA). To evaluate the contribution of the adrenal glands, 4-wk-old spontaneously hypertensive rats (SHR) were sham operated or adrenalectomized. The adrenalectomized SHR were given daily injections of corticosterone and aldosterone. Subsequently, rats were randomized to control or high (8%) dietary Na+, and after 2.5 wk, blood pressure and OLA in plasma, hypothalamus, and pituitary were evaluated. Hypertension developed somewhat less in adrenalectomized vs. sham-operated SHR. On control Na+ intake, adrenalectomy caused only minor decreases in circulating and central OLA. Adrenalectomy did not prevent the 50-90% increases in plasma, hypothalamus, and pituitary OLA caused by high Na+ intake for 2.5 wk. These findings are consistent with the concept that, at least in SHR, the central nervous system may represent the major source of both central and peripheral OLA.
Regulation of glycolytically fueled Ca2+ uptake in smooth muscle plasmalemmal vesicles by phosphorylation
Authors: Hardin C. D. , Zhang C. , Kranias E. G. , Steenaart N. A. , Raeymaekers L. , Paul R. J.
Published: December 2017

A highly purified plasma membrane vesicular preparation from porcine antrum had an endogenous protein kinase activity with substrates of molecular weights of 11, 15, 20.5, 25, 35, 44, 155, and 230 x 10(3). Phosphorylation of the plasma membranes by the endogenous protein kinase activity resulted in a stimulation of initial rates of Ca2+ uptake into inside-out vesicles, which was associated with an increase in the maximum velocity of the Ca2+ pump with no apparent changes in the half-maximal effective concentration for calcium. Because we have previously reported that a membrane-associated glycolytic system may preferentially provide ATP to fuel the Ca2+ pump (9), we examined the effects of phosphorylation on Ca2+ uptake when glycolysis was the sole source of ATP for the pump. We found that the stimulation of Ca2+ uptake by phosphorylation was more pronounced when Ca2+ uptake was supported by glycolysis rather than 2 mM ATP. When ATP was added at a level similar to that produced by endogenous glycolysis, the stimulation of Ca2+ uptake by phosphorylation was comparable to when glycolysis supported the Ca2+ pump. Our observations suggest that the dynamic range (up to threefold) for regulation of the plasmalemmal Ca2+ pump by phosphorylation is considerably larger than previously reported and thus likely to be of physiological significance.
Potassium currents of neurons isolated from medical nucleus tractus solitarius
Authors: Moak J. P. , Kunze D. L.
Published: December 2017

Voltage-dependent potassium currents of neurons enzymatically isolated from the medial and dorsal subnuclei of the solitary tract (mNTS) of adult guinea pig have been characterized with respect to their voltage dependence, time dependence, and sensitivity to specific blocking agents. This region of the medulla receives baroreceptor afferent input and is involved in cardiovascular regulation. Our results showed the presence of three types of potassium currents. First, in all neurons studied (n = 58) a slowly developing outward current was present at potentials more positive than -30 mV. The time to half-peak current decreased with depolarization [24.8 ms at 0 mV; 19.2 ms at +10 mV; 12.5 ms at +20 mV; 9.9 ms at +30 mV (n = 4)]. This current required 20 mM tetraethylammonium (TEA) for full block and failed to show significant inactivation for voltage commands up to 300 ms. Second, a rapidly activating, 4-aminopyridine (4-AP)-sensitive transient outward potassium current was present in 83% of the cells examined (n = 39/47). Threshold for activation was -30 mV. The current relaxation consisted of three components: tau 1 = 14-49 ms; tau 2 = 174-362; tau 3 = 1.1-2.4 s. Finally, in all cells tested calcium activated a large nontransient outward potassium current that was inhibited by charybdotoxin. The studies reported here will be used in conjunction with studies describing sodium and calcium currents to understand the basis for generation of activity in the mNTS in response to baroreceptor input.
NO is more important than PGI2 in maintaining low vascular tone in feto-placental vessels
Authors: Chaudhuri G. , Cuevas J. , Buga G. M. , Ignarro L. J.
Published: December 2017

The endothelial cells of the human umbilical artery and vein release the vasodilators prostacyclin [prostaglandin (PG) I2] and nitric oxide (NO). However, the role of these two substances in the maintenance of vasodilator tone in the feto-placental circulation is not known. Studies were therefore undertaken to compare the relative release of PGI2 and NO from perfused segments (10 cm) of endothelium-intact human umbilical artery (HUA) and vein (HUV) utilizing the cascade bioassay. The endothelium-denuded bovine pulmonary arterial strip was used as the detector tissue because this tissue relaxes equally to various concentrations of PGI2 and S-nitroso-N-acetylpenicillimine (SNAP), which acts by releasing NO. The basal release of NO from the HUA was approximately five times greater than that of PGI2. After stimulation with A-23187, the release of NO from HUV was five to six times greater, and from the HUA, the release was three times greater compared with the PGI2. SNAP was significantly more potent compared with PGI2 in relaxing endothelium-denuded rings of human umbilical and chorionic plate arteries in vitro. These studies suggest that NO is more important than PGI2 for maintenance of low vascular tone in feto-placental vessels, because there is a greater release of NO from the HUA and HUV, and NO is more potent in relaxing endothelium-denuded feto-placental vessels in vitro relative to PGI2.
Rigorous exercise training increases superoxide dismutase activity in ventricular myocardium
Authors: Powers S. K. , Criswell D. , Lawler J. , Martin D. , Lieu F. K. , Ji L. L. , Herb R. A.
Published: December 2017

Controversy exists as to the effect of endurance training on myocardial antioxidant enzyme activity. These experiments sought to clarify this issue by examining antioxidant enzyme activities in the rat ventricular myocardium in response to different intensities and durations of exercise training. Female Fischer-344 rats (120 days old) were assigned to either a sedentary control group or one of nine exercise training groups. Animals were exercised on a motorized treadmill for 10 wk; combinations of three durations (30, 60, and 90 min/day), and three levels of exercise intensity (low, moderate, and high) were studied. Exercise training did not alter (P > 0.05) citrate synthase, catalase, or glutathione peroxidase activities in the right or left ventricle. In contrast, high-intensity exercise (all durations) and moderate-intensity exercise (90 min/day) resulted in a significant increase (P < 0.05; +28–30%) in right ventricular superoxide dismutase (SOD) activity. Similarly, high-intensity exercise training (all durations) resulted in a significant elevation (P < 0.05; +14-26%) of left ventricular SOD activity. Furthermore, low- and moderate-intensity exercise training of long duration (i.e., 60–90 min/day) resulted in significant increases (P < 0.05; +10-23%) in left ventricular SOD activity. These data support the hypothesis that high-intensity exercise (> or = 30 min/day) or moderate-intensity exercise of long duration (> or = 60 min/day) is effective in upregulating SOD activity in the ventricular myocardium.
New experiments on shear modulus of elasticity of arteries
Authors: Deng S. X. , Tomioka J. , Debes J. C. , Fung Y. C.
Published: December 2017

Although the mechanical properties of blood vessels have been studied extensively, the shear modulus of the blood vessel wall is still unknown. New data on the shear modulus of elasticity of rat arteries and its variation with axial stretch and blood pressure are presented. The data were obtained from a new instrument designed and constructed by us to perform simultaneous torsion, inflation, and longitudinal stretching tests. It was found under physiological conditions (pressure = 120 mmHg or 16 kPa; longitudinal stretch = 1.2 relative to zero-stress state), the shear modulus of normal rat thoracic aorta is G = 137 +/- 18 kPa. The difference of shear modulus at body temperature (37 degrees C) and room temperature (25 degrees C) is within 10%. The shear modulus varies significantly with changing longitudinal and circumferential strains in proportion to the strain energy due to these strains. A constitutive equation based on a pseudo strain energy function is proposed. The vessel wall is not transversely isotropic in the incremental sense. When the rat was subjected to high blood pressure due to constriction of its aorta, the shear modulus does not vary significantly with the length of time the animal was subjected to hypertension.
Hydrogen peroxide cytotoxicity in cultured cardiac myocytes is iron dependent
Authors: Byler R. M. , Sherman N. A. , Wallner J. S. , Horwitz L. D.
Published: December 2017

Because of its potential importance in injury during myocardial ischemia and reperfusion, we assessed mechanisms of hydrogen peroxide (H2O2) cytotoxicity in cultured chick embryo cardiac myocytes. Injury was quantitated by release of lactate dehydrogenase (LDH) or 51Cr, both of which correlated with loss of cell viability assessed by trypan blue exclusion. The iron chelator deferoxamine (0.25–2 mM), but not equimolar iron-loaded deferoxamine, markedly reduced LDH and 51Cr release. Injury was also prevented or attenuated by the diffusible reactive oxygen metabolite scavengers dimethylthiourea (10–20 mM) and N-(2-mercaptopropionyl)-glycine (20 mM). The hydroxyl radical scavenger, dimethyl sulfoxide (200–400 mM), also reduced injury. Other scavengers that probably remained extracellular, superoxide dismutase and mannitol, were ineffective. Thus, with exposure of cardiac myocytes to H2O2, cytotoxicity requires reactions catalyzed by intracellular iron.
Chronic hypoxia is associated with reduced delayed rectifier K+ current in rat pulmonary artery muscle cells
Authors: Smirnov S. V. , Robertson T. P. , Ward J. P. , Aaronson P. I.
Published: December 2017

Pulmonary hypertension due to long-term hypoxia occurs as a result of both chronic obstructive pulmonary disease and habitation at high altitudes. Studies in animal models of chronic hypoxia have demonstrated the development of a persistent depolarization of pulmonary artery (PA) smooth muscle cells (SMCs). In seeking to explain this effect, we compared under normoxic conditions the K+ currents in SMCs isolated from small PA of chronically hypoxic and normoxic rats. Chronic hypoxia was associated with a marked (40–50%) reduction in amplitude of a K+ current, which had the pharmacological and kinetic characteristics of a delayed rectifier. The resting potential of the isolated PA cells from chronically hypoxic animals was significantly more positive (-43.5 +/- 2 mV) than that of cells from normoxic animals (-54.3 +/- 2 mV), and this depolarization could be approximately mimicked in the cells from normoxic animals by application of 1 mM 4-aminopyridine, a blocker of the delayed rectifier K+ current. Glibenclamide (1 microM), a blocker of ATP-sensitive K+ (KATP) channels, also caused a substantial (14.5 +/- 2.2 mV) depolarization of the membrane. These results suggest that both delayed rectifier and ATP-dependent K+ currents contribute to setting the membrane potential in these cells and are consistent with the possibility that downregulation of the delayed rectifier K+ current contributes to the depolarization and altered responsiveness to vasoactive agents of PAs that occurs during long-term hypoxia.
Effects of wake and sleep stages on the 24-h autonomic control of blood pressure and heart rate in recumbent men
Authors: Van de Borne P. , Nguyen H. , Biston P. , Linkowski P. , Degaute J. P.
Published: December 2017

Fifteen recumbent young health volunteers underwent 24-h beat-to-beat blood pressure (BP) and interbeat interval (IBI) recordings to explore the effects of wake and polygraphically recorded sleep on the nyctohemeral variations in the spectral frequency components of BP and IBI and in the arterial baroreflex sensitivity (BRS), independent of the confounding effects of changes in posture and physical activity. Spectral analysis of BP and IBI provided markers of sympathetic and vagal controls and of arterial BRS. When falling asleep, the low-frequency (LF) BP and IBI components showed a marked decrease while there was a clear-cut increase in the high-frequency (HF) IBI component. In contrast, only a slight nighttime rapid eye movement-related arterial BRS increase was observed. The final morning awakening induced a pronounced decrease in arterial BRS and the HF IBI component while there was a marked rise in the LF BP component. Hence, a clear 24-h variation in sympathetic and vagal tone but not in arterial BRS persists, independent of changes in activity and position.
A 3,4-diaminopyridine-insensitive, Ca(2+)-independent transient outward K+ current in cardiac ventricular myocytes
Authors: Martin R. L. , Barrington P. L. , Ten Eick R. E.
Published: December 2017

A previously unrecognized current that initially is not present and requires at least 25 min of intracellular access to develop can be found in approximately 75% of cardiac myocytes isolated from cat ventricle within 90 min after intracellular access is obtained with conventional suction patch pipette electrodes. We refer to this patch-duration-dependent (PDD) current as IK(PDD). IK(PDD) can be elicited with depolarizing test steps (Vt) ranging between -40 and +60 mV applied after a hyperpolarizing conditioning step to -140 mV for 200 ms from a holding potential of -40 mV. It shows an ohmic voltage dependence and appears to be an essentially pure K+ current. At Vt = 30 mV, the current is a time-dependent, transient current with a time to peak of 1.06 +/- 0.10 ms (n = 5) and a decay phase that can be fit to the sum of two decaying exponentials (tau f = 3.30 +/- 0.51 ms and tau s = 2.48 +/- 5.6 ms; n = 5). The voltage dependence of the steady-state inactivation can be fit to a single exponential Boltzmann distribution with a slope factor of 8.97 mV, and the voltage at which 50% of the channels are inactivated is -78 mV. The current can be blocked by 0.2 mM Ba2+ extracellularly applied or Cs+ intracellularly applied but is insensitive to 0.5 mM 3,4-diaminopyridine. These characteristics are unlike those for other known K+ currents. The lack of similarity between IK(PDD) and any currently documented cardiac K+ current suggests that IK(PDD) is either a previously undescribed K+ current or a modification of IK1 that makes it adopt an ohmic nature transiently, even in the presence of millimolar internal Mg2+.
Role of ouabainlike compound in rats with reduced renal mass-saline hypertension
Authors: Yamada K. , Goto A. , Hui C. , Yagi N. , Nagoshi H. , Sasabe M. , Sugimoto T.
Published: December 2017

Ouabainlike compound (OLC) has recently been identified as a likely mammalian endogenous digitalis-like factor (EDLF) from human plasma. In this study, plasma levels of OLC were determined to assess the role of OLC in a model known as volume-expanded, reduced renal mass (RRM)-saline (S) hypertension in rats with use of a newly developed radioimmunoassay for ouabain. In the first experiment, at 3 wk after subtotal nephrectomy and drinking 1% saline solution, sysolic blood pressure (SBP) of 18 rats with reduced renal mass (RRM-S rats) was significantly higher than in 17 sham-operated saline-drinking control (C-S) rats [154 +/- 4 (SE) vs. 132 +/- 2 mmHg; P < 0.01]. Plasma OLC levels were 355 +/- 68 pmol/l in RRM-S rats, sevenfold higher than in C-S rats (54 +/- 4 pmol/l; P < 0.01). In the second experiment, we measured plasma OLC levels of 10 RRM-S, 12 sham-operated control (C), and 10 subtotally nephrectomized rats drinking distilled water (RRM rats). Concomitant with a marked increase in blood pressure (203 +/- 5 mmHg), RRM-S rats showed significantly higher plasma OLC levels compared with C and RRM rats (RRM-S 114 +/- 24, C 47 +/- 11, and RRM 52 +/- 9 pmol/l; P < 0.05). In both experiments, plasma OLC levels correlated significantly with SBP (P < 0.05). These findings suggest that plasma OLC shows a similar behavior to that of EDLFs or Na(+)-K(+)-adenosinetriphosphatase inhibitors reported in previous publications and may play a role in hypertensive mechanisms in rats with RRM and excess Na intake.
Differential effects of wave reflections and peripheral resistance on aortic blood pressure: a model-based study
Authors: Berger D. S. , Li J. K. , Noordergraaf A.
Published: December 2017

It has been generally accepted that arterial system wave reflections act to increase aortic blood pressure and the load placed on the left ventricle. Using a mathematical model of the coupled left ventricle-arterial system, we predict that this is not the case. With the model, two aspects of wave reflection, the global reflection coefficient [TG(omega)] and the pulse wave velocity (cph), were adjusted independently. In addition, TG(omega) and cph could be altered independently of the direct-current properties of the arterial system model. Reduction of TG(omega) yielded increases in stroke volume (SV) as well as in peak systolic (Ps), diastolic (Pd), and mean aortic (Pao) pressures and, hence, increased the load on the left ventricle. SV and Pao increased only in the range where strong reflection occurs. Reduced cph also yielded higher pressures, whereas increased cph resulted in reduced Pao and Pd but increased Ps. The changes in pressures and SV in response to altered TG(omega) and cph were relatively small compared with absolute levels. Simulated vasoconstriction and vasodilation further demonstrated the much greater importance of peripheral resistance on pressure and SV levels and lead to the prediction that pressure reduction in vasodilation occurs not because of, but in spite of, reduced wave reflections. We conclude that these results have not yet been observed experimentally, because reflection cannot yet be separated from the direct-current properties of the arterial system; therefore wave reflections themselves have not yet been adequately studied in the intact animal.
Effect of chronic renal medullary nitric oxide inhibition on blood pressure
Authors: Mattson D. L. , Lu S. , Nakanishi K. , Papanek P. E. , Cowley A. W.
Published: December 2017

The effects of chronic nitric oxide inhibition in the renal medulla on renal cortical and medullary blood flow, sodium balance, and blood pressure were evaluated in conscious uninephrectomized Sprague-Dawley rats. During a 5-day renal medullary interstitial infusion of the nitric oxide inhibitor NG-nitro-L-arginine methyl ester (L-NAME, 120 micrograms/h) in saline (0.5 ml/min), renal medullary blood flow was selectively decreased by 30% after 2 h and was maintained at that level for the entire infusion. The decrease in medullary blood flow was associated with sodium retention and increased blood pressure. After the cessation of L-NAME infusion, medullary blood flow returned to control, and the sodium balance became negative as blood pressure returned to baseline. These data indicate that renal medullary nitric oxide plays an important role in the regulation of renal blood flow, sodium excretion, and blood pressure.
Cellular functions of diabetic cardiomyocytes: contractility, rapid-cooling contracture, and ryanodine binding
Authors: Yu Z. , Tibbits G. F. , McNeill J. H.
Published: December 2017

To study the mechanisms of cardiac dysfunction in experimental diabetes, adult rat cardiomyocyte shortening (measured with a video edge-detector system), the sarcoplasmic reticulum (SR) Ca2+ content [assessed by rapid-cooling contracture (RCC) and caffeine contracture (CC)] was examined. Ryanodine binding to the SR Ca(2+)-release channel of myocardium homogenate was also studied. Myocytes from diabetic rats showed depressed shortening (44% decrease compared with controls), reduced maximum rates of shortening and relengthening (58 and 56% decrease, respectively), and prolonged time to peak shortening (47% increase). RCCs and CCs from diabetic cells were 68 and 75% of the control values, respectively. Most of these cardiomyocyte abnormalities were corrected by daily insulin treatment in the diabetic rats. Ryanodine binding parameters indicated that the number of high-affinity binding sites was decreased in diabetic hearts. These data suggest that changes in contractile parameters as measured in diabetic myocytes are in good agreement with data obtained from intact heart or cardiac tissue preparations. Decreased SR Ca2+ content and reduced ryanodine binding sites indicate that the SR functions of storage and release of Ca2+ were depressed. This consequently may cause depressed contraction in diabetic hearts.
Regional differentiation in rat aorta: L-arginine metabolism and cGMP content in vitro
Authors: Abbott R. E. , Schachter D.
Published: December 2017

Sequential segments of rat aorta incubated in vitro exhibit a characteristic activity pattern for the metabolism of L-arginine, the substrate for nitric oxide synthase, and for the content of guanosine 3',5'-cyclic monophosphate (cGMP), the mediator of nitric oxide relaxation of vascular smooth muscle. Highest values were observed just distal to the arch and diminish peripherally. Prior removal of the endothelium, treatment with ouabain, or replacement of ambient medium Na+ decreased L-arginine uptake and metabolism and eliminated the pattern of regional differentiation. Removal of endothelium reduced the cGMP content with loss of the regional pattern. A favorable extracellular/intracellular Na+ gradient is required for the moiety of L-arginine uptake destined for metabolism in the endothelial cell. Replacement of ambient Na+ or treatment with ouabain also decreases markedly the L-arginine metabolism and uptake in cultured rat aortic endothelial cells. When aortic segments were tested with five additional substances, L-leucine uptake alone followed a regional pattern similar to that for L-arginine, and no such pattern was observed for the uptake of L-alanine, alpha-aminoisobutyrate, 3-methylglucose, or Ca2+.
Mechanism of acetylcholine action on membrane potential of endothelium of intact rat aorta
Authors: Marchenko S. M. , Sage S. O.
Published: December 2017

The membrane potential of the endothelium of isolated rat aorta was recorded using the patch-clamp technique. The inhibitor of phospholipase C, U-73122, reduced or abolished the electrical response of the endothelium evoked by acetylcholine, but its inactive analogue, U-73343, was without effect. Depletion of intracellular Ca2+ stores with thapsigargin, cyclopiazonic acid, 2,5-di-(tertbutyl)-1,4-benzohydroquinone, or ionomycin evoked an acetylcholine-like response, which in some aortas included oscillations in endothelial membrane potential and abolished electrical responses evoked by acetylcholine. All stages of acetylcholine- and ionomycin-evoked responses could be evoked in endothelium isolated from underlying smooth muscle. Buffering of intracellular Ca2+ with 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid reduced or abolished acetylcholine-evoked responses. Both buffering of intracellular Ca2+ and inhibition of phospholipase C abolished the inhibitory effect of acetylcholine on phenylephrine-evoked oscillations in endothelial membrane potential. These results suggest that acetylcholine exerts its effect on the membrane potential of intact rat aorta through activation of phospholipase C, the release of Ca2+ from intracellular stores, and so the elevation of intracellular Ca2+ by a mechanism typical for inositol(1,4,5)-trisphosphate-mediated responses.
NADH oxidoreductase is a major source of superoxide anion in bovine coronary artery endothelium
Authors: Mohazzab K. M. , Kaminski P. M. , Wolin M. S.
Published: December 2017

In this study we examined the intracellular sources of superoxide anion (O2-.) in cultured bovine coronary endothelium, employing lucigenin (250 microM)-elicited chemiluminescence (CL). In the homogenate from these cells, 100 microM NADPH increased O2-. by 81% from 8.9 +/- 1.5 to 16.0 +/- 1.5 x 10(5) cpm/mg protein (P < 0.01, n = 8). In the presence of 100 microM NADH, however, CL increased by 458% from 8.9 +/- 1.6 to 49.6 +/- 12.0 x 10(5) cpm/mg protein (P < 0.01, n = 8). Scavengers of O2-., superoxide dismutase (100 micrograms/ml), or 4,5-dihydroxy-1,3-benzenedisulfonic acid disodium salt (Tiron, 10 mM) inhibited NADH-mediated CL by 70 and 83%, respectively. Neither hypoxanthine (100 microM) nor antimycin (10 microM)+succinate (5 mM) had any significant effect on basal CL levels, thereby excluding xanthine oxidase and mitochondria, respectively, as a detectable sources of O2-. generation. The presence of NAD+ (100 microM) and lactate (1 mM) increased CL by 88% (n = 8, P < 0.01). In the intact cells, basal production of CL was increased by 205% (P < 0.01) by 5 mM lactate, but not by 5 mM pyruvate, and CL was inhibited by 10 mM Tiron, suggesting the reduction of cytosolic NAD by lactate dehydrogenase stimulates O2-. production. Diphenyliodonium at 1 and 10 microM inhibited both NADH-mediated CL in homogenate and lactate-mediated CL in intact endothelium by 50 and 33%, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)
Furazolidone increases thapsigargin-sensitive Ca(2+)-ATPase in chick cardiac myocytes
Authors: Lax D. , Martinez-Zaguilan R. , Gillies R. J.
Published: December 2017

Furazolidone is a nitrofuran antibiotic that causes dilated cardiomyopathy in turkeys and chicks and serves as an important model of human dilated cardiomyopathy. The mechanism by which furazolidone produces cardiac injury remains unknown. We investigated the hypothesis that furazolidone alters Ca2+ homeostasis in cardiac muscle cells. Myocytes harvested from 7-day-old chick embryos were treated with furazolidone (0.02, 0.1, and 1 mM) for 24–52 h and then coloaded with seminaphthorhodafluor-1 (SNARF 1) and fura 2 to measure simultaneously intracellular pH (pHi) and intracellular Ca2+ concentration ([Ca2+]i), respectively. Furazolidone did not affect steady-state [Ca2+]i levels in cardiac myocytes. Na+ removal was associated with a rapid increase in [Ca2+]i due to the Na+/Ca2+ exchanger, which was similar in control and furazolidone-treated cells. The rate of [Ca2+]i recovery after Na+ removal was significantly increased in the furazolidone-treated cells compared with controls. In most cells, recovery from Ca2+ load is accomplished by the activity of Ca(2+)-adenosinetriphosphatases (ATPases). Thapsigargin, inhibitor of sarcoplasmic reticulum Ca(2+)-ATPase, prevented the furazolidone-induced changes. These results demonstrate that furazolidone increases the activity of thapsigargin-sensitive Ca(2+)-ATPase without affecting Na+/Ca2+ exchange. These data enhance our understanding of the mechanism of furazolidone-induced injury in cardiac myocytes and may be useful in determining mechanisms of injury in dilated cardiomyopathy.
Effects of maturation on alpha-adrenergic receptor affinity and occupancy in small cerebral arteries
Authors: Elliott S. R. , Pearce W. J.
Published: December 2017

The present experiments examine the hypothesis that changes in receptor affinity and occupation mediate maturational changes in norepinephrine sensitivity in small cerebral arteries. In second-order (2B) and fourth-order (4B) branch middle cerebral artery segments from newborn and adult sheep, we first found that a stretch ratio based on artery diameter better estimated optimal prestretch than did passive tension. Next, we determined norepinephrine dose-response relations before and after prazosin, yohimbine, and benextramine. Prazosin competitively blocked contractions to norepinephrine, but yohimbine had no effect, indicating that alpha 1-adrenoceptors mediated contraction. Norepinephrine sensitivity [determined from the -log of the half-maximal effective dose (pD2)], maximal response, and binding affinity all decreased with age in 4B but not 2B segments. Receptor occupancy at the pD2 increased with age only in 2B segments. In conclusion, maturation of ovine middle cerebral arteries involves branch-specific changes in affinity and receptor occupation of the alpha 1-adrenoceptors that mediate contractile responses to norepinephrine. Age-related changes in receptor density and/or intrinsic efficacy probably are involved also.
Bioenergetics and control of oxygen consumption in the in situ rat heart
Authors: Headrick J. P. , Dobson G. P. , Williams J. P. , McKirdy J. C. , Jordan L. , Willis R. J.
Published: December 2017

Control of respiration by products of ATP hydrolysis was examined in the in situ rat heart using a purpose-built nuclear magnetic resonance (NMR) coil. The in situ ratio of phosphocreatine to ATP concentrations ([PCr]/[ATP]) was 2.30 +/- 0.05, free Mg2+ concentration ([Mg2+]) was 0.57 mM, and cytosolic pH was 7.35 +/- 0.03 (n = 7). Basal inorganic phosphate concentration ([Pi]) was below NMR detection but was estimated to be 0.83 mM. The [ATP]/[ADP] [Pi] ratio, free ADP concentration ([ADP]), and free energy of ATP hydrolyses (delta GATP) were calculated to be 700,000 +/- 78,000 M-1, 18 +/- 3 microM, and -63.93 +/- 0.33 kJ/mol in situ, respectively (n = 7). In contrast, in the Langendorff perfused rat heart [ATP]/[ADP] [Pi] was only 76,140 +/- 12,830 M-1, [ADP] was 65 +/- 9 microM, and delta GATP was -59.92 +/- 0.48 kJ/mol (n = 7), all indicative of a lower energy state in vitro. Epinephrine infusion in situ (0.9 microgram.min-1.kg-1) increased the rate-pressure product 2.05-fold. During stimulation [ATP] was stable at 97 +/- 3% signal intensity, [PCr] declined by 25%, and [Pi] increased to 1.83 mM. Cytosolic pH was 7.27 +/- 0.01 and [Mg2+] was 0.64 +/- 0.05 mM. [PCr]/[ATP] declined to 1.83 +/- 0.13, and [ATP]/[ADP] [Pi] fell to 108,000 +/- 15,000 M-1. delta GATP only fell marginally to -59.56 +/- 0.49 kJ/mol. Free [ADP] increased threefold to 55 +/- 10 microM. Infusion of 2.8 +/- 0.5 microgram.min-1.kg-1 epinephrine increased the rate-pressure product 2.7-fold, further reduced [ATP]/[ADP] [Pi] (5% of basal), and elevated [ADP] more than fourfold without changing [ATP]. We conclude that the in situ heart is highly energetic compared with isolated perfused hearts and operates at a different metabolic "set-point." Because free [ADP] and [Pi] in situ approximate apparent Michaelis constants for mitochondrial respiration in vitro and increase with increased cardiac work, we conclude that each fulfills the criteria for the kinetic control of O2 consumption in the in situ rat myocardium.
Simulation of O2 transport in skeletal muscle: diffusive exchange between arterioles and capillaries
Authors: Secomb T. W. , Hsu R.
Published: December 2017

Theoretical simulations of oxygen transport in skeletal muscle are used to study the role of arterioles in oxygen delivery. A three-dimensional configuration of capillaries and arterioles in a cuboidal tissue region is simulated, based on observations of hamster cheek pouch retractor muscle. Equations describing convective and diffusive oxygen transport are solved using a Green's function method. In resting muscle, predicted oxygen saturation of capillary blood increases as it flows toward arterioles, and adjacent capillaries flowing in opposite directions show very similar variations in saturation. Diffusive oxygen loss from arterioles equals about 85% of consumption. Capillaries absorb much of this oxygen (equal to approximately 45% of consumption) and deliver it at downstream locations. Thus diffusive exchange between arterioles and capillaries plays an important part in distributing oxygen throughout the tissue. At higher flow and consumption rates, the relative amounts of oxygen diffusing out of arterioles and into capillaries decrease. The results are consistent with the hypothesis that oxygen content of arteriolar blood participates in metabolic regulation of blood flow.