bluuebunny/crossref_metadata_2025 huggingface dataset:
Sublethal ischemia alters myocardial antioxidant activity in canine heart
Authors: Hoshida S. , Kuzuya T. , Fuji H. , Yamashita N. , Oe H. , Hori M. , Suzuki K. , Taniguchi N. , Tada M.
Published: December 2017

We examined antioxidant activity in the pre-conditioned canine myocardium with four 5-min episodes of regional ischemia and reperfusion. Immediately after repetitive brief ischemia, mitochondrial Mn-superoxide dismutase (SOD) activity in the ischemic myocardium significantly increased compared with that in the nonischemic myocardium (18.7 +/- 2.1 vs. 14.9 +/- 1.0 U/mg protein, P < 0.05). Although no difference was seen in the activity between these regions after 3 h of the sublethal ischemia, a significant increase in the activity of the ischemic myocardium reappeared after 24 h compared with that of the nonischemic myocardium (26.7 +/- 0.9 vs. 20.8 +/- 0.9 U/mg protein, P < 0.05). Mn-SOD content increased gradually in the ischemic myocardium after sublethal ischemia, with a peak after 24 h (2.8 +/- 0.1 vs. 2.1 +/- 0.1 microgram/mg protein, P < 0.05). There were no differences in the activity and content of Cu, Zn-SOD between these regions after sublethal ischemia. Activities of glutathione peroxidase and reductase were significantly higher and lower, respectively, in the ischemic myocardium than those of the nonischemic myocardium immediately after repetitive brief ischemia, but no differences between these regions were seen in activities after 3 or 24 h. These results indicate that a brief ischemic insult alters myocardial antioxidant activity not only immediately after but also 24 h after sublethal ischemia.
Angiotensin II enhancement of hormone-stimulated cAMP formation in cultured vascular smooth muscle cells
Authors: Kubalak S. W. , Webb J. G.
Published: December 2017

The mechanism by which angiotensin II (ANG II) potentiates hormone-induced adenosine 3',5'-cyclic monophosphate (cAMP) formation was studied in cultured rat vascular smooth muscle cells. Incubation of cells for 60 s with 100 nM ANG II produced a two- to threefold enhancement of cAMP stimulation when coupled with isoproterenol, prostaglandin I2, or adenosine. ANG II also enhanced cAMP formation when adenylyl cyclase was stimulated directly with forskolin or activated through the stimulatory guanyl nucleotide-binding protein (Gs) with cholera toxin. Forskolin stimulation was increased by only 40%, but cholera toxin-stimulated cAMP formation was doubled. Activation of protein kinase C with phorbol 12-myristate 13-acetate (PMA) enhanced isoproterenol-stimulated cAMP by 51%, but inhibitors of protein kinase activation had little effect on ANG II enhancement of cAMP production. However, use of PMA to cause feedback inhibition of D-myo-inositol 1,4,5-trisphosphate [Ins(1,4,5)P3] formation blocked the effect of ANG II on agonist-stimulated cAMP formation, and the time course for this effect of PMA paralleled its inhibitory effect on Ins(1,4,5)P3 production. Furthermore, chelation of intracellular Ca2+ or treatment with calmodulin antagonists also diminished the synergism between ANG II and isoproterenol for cAMP stimulation. The results indicate that ANG II enhances cAMP formation in vascular smooth muscle cells by facilitating the interaction between activated Gs and adenylyl cyclase. In addition, the data suggest that this effect of ANG II is directly related to Ins(1,4,5)P3 stimulation and appears to involve a Ca(2+)-calmodulin-dependent mechanism.
Analysis of responses to substance P in the pulmonary vascular bed of the cat
Authors: McMahon T. J. , Kadowitz P. J.
Published: December 2017

Responses to substance P were investigated in the pulmonary vascular bed of the cat with controlled pulmonary blood flow and constant left atrial pressure. Under baseline conditions, intralobar injections of substance P caused small, inconsistent reductions in lobar arterial pressure (AP) and significant reductions in mean systemic AP without affecting left atrial pressure. Decreases in lobar AP were significant and dose related when lobar vascular resistance was increased with U-46619, a thromboxane A2 mimetic. When compared with other vasodilator agents, the order of potency was substance P approximately bradykinin > pituitary adenylate cyclase activating polypeptide (PACAP) > acetylcholine (in nmol). Pulmonary vasodilator responses to substance P were unchanged by administration of atropine, glibenclamide, or sodium meclofenamate or when airflow to the left lower lung lobe was interrupted by bronchial occlusion. The NO synthesis inhibitor, N omega-nitro-L-argininemethyl ester (L-NAME), and the soluble guanylate cyclase inhibitor, methylene blue (MB), selectively inhibited pulmonary vasodilator responses to substance P and to acetylcholine. MB or L-NAME had no significant effect on pulmonary vasodilator responses to albuterol, lemakalim, or PACAP, whereas MB inhibited and L-NAME enhanced vasodilator responses to NO and sodium nitroprusside. The present investigation demonstrates that, when tone is increased experimentally, substance P has potent pulmonary vasodilator activity, and responses are not dependent on changes in bronchomotor tone, on the activation of muscarinic receptors or ATP-sensitive K+ channels, or on the release of a dilator prostaglandin but do involve, at least in part, endothelium-derived NO release and soluble guanylate cyclase activation.
Induction of NO production by TNF-alpha and lipopolysaccharide in porcine coronary arteries without endothelium
Authors: Shibano T. , Vanhoutte P. M.
Published: December 2017

The effects of tumor necrosis factor-alpha (TNF-alpha) and lipopolysaccharide (LPS) were studied in porcine coronary arteries without endothelium. Rings of the artery were incubated in minimum essential medium with TNF-alpha or LPS for 6 or 24 h. After 6 h incubation, the rings were suspended in organ chambers filled with physiological salt solution containing indomethacin for the measurement of isometric force. The rings were contracted with prostaglandin F2 alpha before the addition of L-arginine. In rings treated with TNF-alpha or LPS, L-arginine caused a concentration-dependent relaxation that was abolished by N omega-nitro-L-arginine [an inhibitor of nitric oxide (NO) synthase]. However, contractions to 5-hydroxytryptamine were not affected by TNF-alpha and LPS. After 24 h of incubation, TNF and LPS impaired the contractions to 5-hydroxytryptamine and increased the accumulation of nitrite, a stable degradation product of NO. These effects of TNF-alpha and LPS were blocked by N omega-nitro-L-arginine. Cycloheximide (an inhibitor of protein synthesis) attenuated the inhibitory effect of TNF-alpha and LPS on contractions to 5-hydroxytryptamine. Thus, in the porcine coronary artery without endothelium, TNF-alpha and LPS can induce an L-arginine-NO pathway.
Single calcium channels in resistance-sized cerebral arteries from rats
Authors: Quayle J. M. , McCarron J. G. , Asbury J. R. , Nelson M. T.
Published: December 2017

Unitary currents through single calcium channels were measured from cell-attached patches on smooth muscle cells isolated from resistance-sized branches of posterior cerebral arteries from Wistar-Kyoto normotensive rats. Barium (80 and 10 mM) was used as the charge carrier, with and without the dihydropyridine calcium channel agonist BAY R 5417. Unitary currents decreased on membrane depolarization, with a slope conductance of 19.4 pS (80 mM barium). Channel open-state probability (Po) was steeply voltage dependent. Peak Po during test pulses from -70 mV increased e-fold per 4.5-mV depolarization. Mean peak Po at potentials positive to +10 mV was 0.44. Po at steady membrane potentials was also steeply voltage dependent, changing e-fold per 4.5 mV in the absence of inactivation. Steady-state Po at positive potentials was substantially lower than peak Po elicited by test pulses, suggesting that steady-state inactivation can reduce Po by as much as 10-fold. Membrane depolarization decreased the longest mean closed time but had little effect on the mean open time of single calcium channels measured during steady-state recordings. Lowering the external barium concentration from 80 to 10 mM reduced the single channel conductance to 12.4 pS and shifted the relationship between steady-state Po and membrane potential by about -30 mV. BAY R 5417 also shifted this relationship by about -15 mV.
Activation of cardiac KATP channels: an endogenous protective mechanism during repetitive ischemia
Authors: Yao Z. , Cavero I. , Gross G. J.
Published: December 2017

The role of KATP channels in myocardial stunning produced by repetitive coronary occlusions was studied in barbital-anesthetized dogs. Regional percent segment function (%SS) was measured by sonomicrometry, and the monophasic action potential (MAP) in the ischemic region was measured by an epicardial probe. Under control conditions, six 5-min periods of coronary occlusion, interspersed with 10-min periods of reperfusion, and ultimately followed by 2 h of reperfusion produced regional segment dysfunction and a similar rate and amount of shortening of the MAP measured at 50% repolarization duration (MAPD50) during each successive ischemic period. Pretreatment with glibenclamide (0.3 mg/kg iv), a KATP channel antagonist, significantly prevented the reduction of MAPD50, particularly during the first occlusion period, and it worsened postischemic dysfunction. In contrast, pretreatment with aprikalim (10 micrograms/kg bolus +/- 0.1 microgram.kg-1.min-1 iv), a KATP channel opener, accelerated the rate and extent of shortening of MAPD50 during each occlusion and markedly improved %SS throughout reperfusion. Pretreatment with d-sotalol (2 mg/kg iv), an antagonist of voltage-dependent K+ channels, significantly prolonged MAPD50 of the ischemic region before coronary occlusion but did not alter the rate of shortening of MAPD50 during ischemia and did not affect the recovery of %SS. These results indicate that activation of KATP channels during ischemia with the resultant shortening of the MAPD50 is an endogenous adaptive mechanism that affords functional myocardial protection during repetitive, brief periods of coronary arterial occlusion.
Dextran increases survival of subconfluent endothelial cells exposed to shear stress
Authors: Wechezak A. R. , Coan D. E. , Viggers R. F. , Sauvage L. R.
Published: December 2017

In vitro devices in combination with cultured cells have been used to study the relationship between shear stress and endothelial injury. Almost exclusively, these investigations have used confluent monolayers and conventional culture media as perfusates and reported little cell loss over a wide range of shear stress conditions. In this investigation when subconfluent endothelial cells were exposed to 22 and 88 dyn/cm2 for 2, 8, and 24 h in a perfusate of medium and 5% serum, a progressive cell loss was observed. Lower cell densities were a product of decreased cell proliferation as measured by bromodeoxyuridine (BrdU) incorporation and loss of the initial cell population. Video recordings indicated that cells characteristically detached by proximal cell peeling from the substrate and an aneurysmal rupture of the cell membrane. Cell retention was increased by including 250 and 475 microM neutral dextran (70 kDa) in perfusates. Experimental evidence suggests dextran does not directly stimulate proliferation or correct an osmotic imbalance. This investigation has substantiated that fluid-generated shear stress can cause endothelial denudation and that conditions (subconfluency, time, and perfusate supplementation) under which shear stress is applied are as important for cell survival as shear stress magnitude.
Cardiovascular responses to adenosine in fetal sheep: autonomic blockade
Authors: Koos B. J. , Mason B. A. , Ducsay C. A.
Published: December 2017

The mechanism by which adenosine increases heart rate was investigated in 21 chronically catheterized fetal sheep (> 0.8 term). Intra-arterial infusion of adenosine (0.16 mg.min-1.kg fetal wt-1) for 1 h significantly increased fetal heart rate within 5 min with maximum values of approximately 68 beats/min above the control mean of 163 +/- 8 beats/min. The average diastolic blood pressure was reduced only during the first 10 min of infusion, and the average systolic and mean arterial pressures were not significantly affected. Mean venous pressure rose by approximately 48% after 20 min of adenosine infusion, but all other measurements did not differ significantly from the control value. The mean hemoglobin concentration during the last 30 min of infusion was increased by approximately 8%. Plasma concentrations of norepinephrine and epinephrine were elevated only during the first 30 min of adenosine administration, to values as high as 2.3 and 5 times the respective control mean. Adenosine significantly increased mean fetal heart rate by about 15-20 beats/min in fetuses with autonomic ganglion blockade or combined cholinergic, alpha-, and beta-adrenergic receptor blockade. Intra-arterial infusion of CGS 21680C, an A2-adenosine receptor agonist, also produced a fetal tachycardia of approximately 86 beats/min above the control mean and increased intrinsic fetal heart rate by approximately 38 beats/min. It is concluded that approximately 75% of the positive chronotropic effects of adenosine are produced by A2-receptor stimulation of the autonomic nervous system and that approximately 25% of the rise in heart rate induced by adenosine may be caused by activation of A2-receptors in myocardium.
alpha-Adrenergic augmentation of myogenic response in rat arterioles: role of protein kinase C
Authors: Watanabe J. , Keitoku M. , Hangai K. , Karibe A. , Takishima T.
Published: December 2017

We tested the hypothesis that protein kinase C (PKC) activation plays a major role in alpha-adrenergic augmentation of the myogenic response in rat isolated arterioles. Lumen diameter measured was with a video-monitored microscopic system. Lumen diameter did not change (131 +/- 5 vs. 126 +/- 6 microns) despite an increase in lumen pressure from 40 to 100 mmHg. Phenylephrine (Phe; 3 x 10(-7) M) augmented the myogenic response, since lumen diameter decreased significantly from 117 +/- 8 to 101 +/- 8 microns. High potassium (40 mM) failed to augment the myogenic response, while constricting the vessels to nearly the same extent as did Phe. PKC inhibitors 1-(5-isoquinolinylsulfonyl)-2-methylpiperazine dihydrochloride (H-7, 5 x 10(-5) M, n = 7) and staurosporine (3 x 10(-9) M, n = 7) abolished the Phe-induced augmentation. H-7 and staurosporine depressed the myogenic response even without Phe. PKC activators phorbol 12,13-dibutyrate (3 x 10(-9) M; n = 7) and 4 beta-phorbol 12-myristate 13-acetate (6 x 10(-8) M; n = 6) constricted the vessels by 11 +/- 2 and 18 +/- 3%, respectively. However, PKC activators failed to augment the myogenic response. These results suggest that PKC activation does not play a major role in alpha-adrenergic augmentation of the myogenic response in rat skeletal arterioles.
Enantiomeric dissection of the effects of the inotropic agent, EMD 53998, in single cardiac myocytes
Authors: Gambassi G. , Capogrossi M. C. , Klockow M. , Lakatta E. G.
Published: December 2017

The effects of the thiadiazinone derivative, 5-[1-(3,4-dimethoxybenzoyl)-1,2,3,4-tetrahydrochinolin-6-yl]-6-met hyl-3,6- dihydro-2H-1,3,4-thiadiazin-2-on (EMD 53998), and of its (+)EMD 57033 and (-)EMD 57439 enantiomers, were tested on the contractile properties and cytosolic [Ca2+] ([Ca2+]i) transients of single intact guinea pig cardiac myocytes. Cells were loaded with the ester form of the fluorescent probe, indo-1, and bathed in a N-2-hydroxyethyl-piperazine-N'-2-ethanesulfonic acid-buffered solution at 25 degrees C (1 mM of CaCl2, 1 Hz stimulation rate). All three substances exerted a pronounced increase in twitch amplitude: the maximal effect of the racemate (380% of control value) was approximately the sum of the effects of its two enantiomers (186 and 236% of control value for the (+)- and (-)-enantiomer, respectively). The [Ca2+]i transient, measured as the 410-to-490 nm indo-1 fluorescence ratio transient after excitation, was increased by the racemate and its (-)-enantiomer (172 and 152% of control value, respectively), but was not increased by the (+)-enantiomer. The racemate and the (-)-enantiomer, but not the (+)-enantiomer, markedly reduced the contraction duration and [Ca2+]i transient duration. In unstimulated cells resting length was significantly reduced by the (+)-enantiomer, and this was accompanied by a decrease in indo-1 fluorescence; the (-)-enantiomer had no effect on either parameter. In the presence of 2,3 butanedione monoxime (BDM), which markedly reduces twitch amplitude by inhibiting cross-bridge mechanics, addition of the (+)-enantiomer restored the twitch contraction to above the pre-BDM level without augmenting the [Ca2+]i transient. In contrast, the (-)-enantiomer failed to reverse the BDM-induced contractile depression, even though it caused a significant increase of the [Ca2+]i transient. Thus, in intact cells the positive inotropic effect of EMD 53998 is due to specific properties of its enantiomers: the (-)-enantiomer has adenosine 3',5'-cyclic monophosphate-like effects (increase in amplitude and reduction of [Ca2+]i transient and contraction durations), whereas the (+)-enantiomer enhances the myofilament-Ca2+ interaction.
Functional distribution of coronary vascular volume in beating goat hearts
Authors: van der Ploeg C. P. , Dankelman J. , Spaan J. A.
Published: December 2017

With use of hemoglobin-bound O2 as an endogenous tracer, intramyocardial blood volume distribution between vessels involved in O2 exchange and more distal vessels was estimated. In nine anesthetized open-chest goats, the left main coronary artery was cannulated and perfused at a constant flow. Coronary arteriovenous O2 content difference (AVOX) was measured. AVOX transients induced by a flow step could be characterized by two phases: delay time and slow change to a new steady state. AVOX responses were fitted by a two-compartment model consisting of a well-mixed compartment from which O2 is consumed with volume Vm, and a distal unmixed compartment without O2 exchange, with volume Vunm. The rate of change of the AVOX transient depends on Vm, whereas the delay time depends on Vunm. Measurements in nine goats resulted in a Vm value of 9.9 +/- 1.1 (SE) ml/100 g (n = 9) and a Vunm value of 3.8 +/- 0.3 ml/100 g. Maximal vasodilation caused a significant increase in Vm (13.1 +/- 1.3 ml/100 g; n = 5), whereas Vunm did not change (5.0 +/- 0.5 ml/100 g). Hence, the increase of intramyocardial blood volume induced by vasodilation must be expected in the capillary bed and not in the coronary veins.
Effects of diabetes on myocardial glucose transport system in rats: implications for diabetic cardiomyopathy
Authors: Garvey W. T. , Hardin D. , Juhaszova M. , Dominguez J. H.
Published: December 2017

Biochemical mechanisms underlying impaired myocardial glucose utilization in diabetes mellitus have not been elucidated. We studied sarcolemmal vesicles (SL) in control, streptozotocin-induced diabetic (D), and insulin-treated diabetic (Tx) rats and found that 3-O-methylglucose transport rates were decreased 53% in D rats and were normalized by insulin therapy. Immunoblot analyses of SL revealed that GLUT4 glucose transporters were decreased 56% in D and were normal in Tx rats. Thus diminished transport rates could be fully explained by reduced numbers of SL GLUT4 with normal functional activity. To determine whether SL GLUT4 were decreased due to tissue depletion or abnormal subcellular distribution, we measured GLUT4 in total membranes (SL plus intracellular fractions). Total GLUT4 (per mg membrane protein or per DNA) was decreased 45–51% in D [half time = 3.5 days after streptozotocin], and these values were restored to normal in Tx rats. Also, diabetes decreased GLUT4 mRNA levels by 43%, and this effect was reversed by insulin therapy. We conclude that, in diabetes, 1) impaired myocardial glucose utilization is the result of a decrease in glucose transport activity, and 2) transport rates are reduced due to pretranslational suppression of GLUT4 gene expression and can be corrected by insulin therapy. GLUT4 depletion could limit glucose availability under conditions of increased workload and anoxia and could cause myocardial dysfunction.
Variable cross-bridge cycling-ATP coupling accounts for cardiac mechanoenergetics
Authors: Taylor T. W. , Goto Y. , Suga H.
Published: December 2017

Cardiac twitch contractions were simulated by Huxley's sliding filament cross-bridge muscle model coupled with parallel and series elastic components. The energetics of the contraction were based on the ATP hydrolysis for the cross-bridge cycling. Force-length area (FLA), as a measure of the total mechanical energy, was computed for both isometric and isotonic contractions in a manner similar to the pressure-volume area (PVA) (Suga, H. Physiol. Rev. 70: 247–277, 1990). PVA correlates linearly with cardiac oxygen consumption, and since FLA is analogous to PVA, FLA should correlate with the ATP expended. Simulations comparing FLA with the cross-bridge cycling ATP usage showed that at lower muscle fiber activation levels (shorter initial fiber lengths and lower preload levels) FLA decreased more rapidly than the number of muscle fiber cross-bridge cycles in both isometric and isotonic contraction cases. This suggests that one ATP can cause more than one cross-bridge cycle at lower activation levels as was proposed by Yanagida, Arata, and Oosawa (Nature 316: 366–369, 1985). If the number of cross-bridge cycles to ATP ratio is allowed to increase at lower activation levels as suggested by Yanagida et al., Huxley's model is compatible with the experimental findings on FLA and PVA.
Effects of atrial fibrillation on left and right atrial dimensions, pressures, and compliances
Authors: Leistad E. , Christensen G. , Ilebekk A.
Published: December 2017

The effects of atrial fibrillation on left and right atrial dimensions, pressures, and compliances were examined in two groups of seven barbiturate-anesthetized open-chest pigs. Atrial diameters and pressures were recorded during atrioventricular (AV) pace and thereafter during atrial fibrillation. Both rhythms were studied with constant ventricular rate after complete AV block. Left atrial maximal diameter, which appeared at the end of the atrial filling phase, decreased from 32.4 (28.9-36.7; median and 95% confidence interval) to 31.3 (28.4-35.7) mm after induction of atrial fibrillation. The right atrial maximal diameter also decreased, although not significantly. Atrial pressure at the peak of the v wave rose from 7.0 (5.5-8.5) to 9.6 (8.3-11.2) mmHg in the left atrium and from 5.0 (4.3-5.6) to 7.3 (6.2-8.7) mmHg in the right atrium. Left and right atrial chamber stiffness constants increased from 0.25 (0.19-0.48) to 0.41 (0.28-0.66) mm-1 and from 0.21 (0.11-0.31) to 0.33 (0.30-0.39) mm-1, respectively. Instantaneous diastolic atrial compliance decreased in both atria after induction of atrial fibrillation. Thus, during atrial fibrillation with regular ventricular rate, changes in atrial diameter, pressure, and compliance take place.
Influence of endothelium on induction of the L-arginine-nitric oxide pathway in rat aortas
Authors: Fleming I. , Gray G. A. , Stoclet J. C.
Published: December 2017

The role of the endothelium in the onset and persistence of vascular hyporeactivity induced by bacterial lipopolysaccharide (LPS) and the implication of the L-arginine-nitric oxide (NO) pathway in this phenomenon were investigated in rat aortic rings exposed to LPS for different times. LPS (100 ng/ml) induced a decrease in the contractile response obtained by norepinephrine (NE) in rings without endothelium after a delay of 6 h. This delay was reduced to 4 h in the presence of the endothelium and corresponded temporally with the development of relaxation after addition of L-arginine (1 mM). This effect of L-arginine along with hyporeactivity to NE was reversed by both NG-nitro-L-arginine methyl ester (300 microM) and methylene blue (3 microM). The effects of LPS on reactivity, L-arginine-dependent relaxation, and tissue guanosine 3',5'-cyclic monophosphate content were prevented by cycloheximide (100 micrograms/ml) whether present throughout the experiment or added 6 h after LPS. Increasing the concentration of LPS to 1 mg/ml reduced the delay between addition of LPS and response to L-arginine in endothelium-denuded rings to 4 h but was without effect on the delay observed in rings with endothelium. These results demonstrate that the time course of development of hyporeactivity to NE corresponds to that of activation of the L-arginine-NO pathway after LPS challenge as assessed by development of sensitivity to L-arginine. The induction process was accelerated by the presence of the endothelium, which also increased the sensitivity of the preparation to LPS.(ABSTRACT TRUNCATED AT 250 WORDS)
Continuous assessment of hemodynamic control by complex demodulation of cardiovascular variability
Authors: Hayano J. , Taylor J. A. , Yamada A. , Mukai S. , Hori R. , Asakawa T. , Yokoyama K. , Watanabe Y. , Takata K. , Fujinami T.
Published: December 2017

Usefulness of complex demodulation (CDM) in assessing the frequency components of cardiovascular variability was assessed and, subsequently, this technique was utilized to determine the time-dependent responses of the low-frequency (LF) and high-frequency (HF) amplitudes of heart rate and blood pressure variabilities during postural tilt. CDM provides the time-dependent changes in amplitude of a particular frequency component on a continuous basis. Analysis of simulated data showed that CDM has sufficient frequency resolution to separately measure LF and HF amplitudes with a time resolution < 15 s and that CDM is robust to alterations in the frequency of the components. Analysis of actual data during postural tilt test in 23 young healthy subjects demonstrated that the HF amplitude of heart rate, an index of cardiac parasympathetic tone, rapidly decayed with head-up tilt (P < 0.01) and increased quickly showing an overshoot with tilt back to the supine position (P < 0.01). The LF amplitude of blood pressure, an index of vasomotor sympathetic activity, showed marked rhythmic fluctuation at an interval of 48-100 s during head-up tilt (P < 0.01), synchronizing with similar fluctuation in the LF amplitude of heart rate (P < 0.01). These results suggest that CDM can be used to provide a continuous assessment of cardiovascular variability components and that the dynamic responses of autonomic circulatory control to upright posture result in a phasic modulation of LF amplitude.
A role for nitric oxide in active thermoregulatory vasodilation
Authors: Taylor W. F. , Bishop V. S.
Published: December 2017

We have shown previously that an increase in ear blood flow velocity (EBF) in the conscious, chronically instrumented rabbit during whole body heating (WBH) involves active neurogenic vasodilation that is abolished by local nerve block. This study was designed to test the potential role of nitric oxide (NO) in rabbit ear neurogenic vasodilation during hyperthermia. Rabbits were instrumented for the measurement of arterial pressure, heart rate, and EBF (Doppler ultrasound). A catheter was also placed in the left lingual artery for administration of drugs to the left ear. WBH was achieved by circulating warm water through a rubber pad placed around the rabbit. Internal temperature was measured with a rectal thermocouple. During WBH, bolus injections of N omega-nitro-L-arginine (L-NNA), a false substrate for the formation of NO, were given via the lingual artery (10(-5) M, 4-5 ml total) to determine whether NO was involved in the increase in EBF. During WBH, left ear vascular conductance (EVC) increased from 0.07 +/- 0.03 to 5.87 +/- 0.73 kHz/100 mmHg and right EVC from 0.20 +/- 0.13 to 4.49 +/- 1.73 kHz/100 mmHg. When EVC was maximum, L-NNA was administered into the left lingual artery. EVC began to decrease after a latency of 23 min. At 56 +/- 8 min, left and right EVC had decreased to 0.18 +/- 0.10 and 0.23 +/- 0.11 kHz/100 mmHg, respectively (P < 0.05). Subsequent infusions of L-arginine, the true substrate for NO formation, restored EVC. These results suggest that NO is involved in active vasodilation during heating in the rabbit ear.
Blood-to-tissue clearance vs. lymph analysis in determining capillary transport characteristics for albumin in skin
Authors: Reed R. K. , Ishibashi M. , Townsley M. I. , Parker J. C. , Taylor A. E.
Published: December 2017

The blood-to-tissue clearance of radioactive albumin and a lymphatic flux analysis were used to evaluate the transport properties of albumin in the canine hindpaw. A prenodal lymphatic was cannulated, and lymph was collected for a 2-h control period. Thereafter venous pressure was elevated between 7 and 31 mmHg. After 2 h of increased venous pressure, the radioactive tracer was given intravenously. During the next 2 h lymph was sampled, and at the end of this time tissue and blood samples were obtained. The experiments showed that, of the tracer filtered in excess of control at increased venous pressure, an estimated 21% was cleared via the lymphatics and 79% was retained in the tissue. As a percentage of total tracer flux at increased venous pressure, 9% (measured) was drained by lymph and 91% was retained in the tissue. Of the fluid filtered in excess of control at increased capillary pressure, 70% (measured) was drained via the lymphatics and 30% was retained in the tissue in the same period. Twice the amount of endogenous albumin filtered across the capillary wall was drained via the lymphatics during the experimental period. The lymphatic washout of endogenous albumin from the interstitium will cause an underestimation of the capillary reflection coefficient and overestimation of the permeability-surface area product. Because of the loss of tracer from the tissue, the opposite occurs when the blood-to-tissue clearance of radioactive albumin is used.
Segmental calculation of left ventricular wall stresses
Authors: Regen D. M. , Anversa P. , Capasso J. M.
Published: December 2017

A procedure for calculating left ventricular wall stresses segmentally was devised. Rectangular coordinates of the wall surfaces as seen in longitudinal section were plotted with the long axis as the x-axis. For each cavity point, a third-order polynomial (cubic spline) was fitted to the point together with several adjacent points on either side of it; the cavity radius (normal to cavity surface) at the point was found algebraically from the spline's coefficients. Each cavity radius was matched with the most symmetrical one from the opposite cavity surface. The point of intersection of the cavity radius with the outer surface was found, and a midwall point was identified from logarithmic means of cavity and outer radial lengths. For each midwall point, a cubic spline was fitted to that point together with several adjacent points on either side of it, and the midwall radius at that point was determined algebraically from the spline's coefficients. Each midwall radius was matched to the most symmetrical one from the opposite midwall. The locus of points at equal radial distances from opposite midwalls forms the axis. The midwall radius of curvature (r theta) orthogonal to the meridian at each point was taken as the radial distance from the midwall to the axis. Midwall meridional radius of curvature (r phi) was calculated from the spline's coefficients. Thickness (h) was calculated from intersections between the midwall radius and the inner and outer surfaces. For each point, meridional tension (T phi) was calculated as T phi = Pr theta/2, and hoop tension (T theta) was calculated as T theta = (Pr theta/2)(2 - r theta/r phi) where P is transmural pressure. Stresses were calculated as tensions divided by thicknesses (sigma phi = T phi/h, sigma theta = T theta/h), or more directly as sigma phi = Pr theta/2h and sigma theta = (Pr theta/2h)(2 - r theta/r phi). This procedure was validated with simple chamber shapes, and it has been applied to left ventricles.
A stable L-arginine-dependent relaxing factor released from cytotoxic-activated macrophages
Authors: Uchizumi H. , Hattori R. , Sase K. , Cai W. J. , Kadota K. , Sasayama S. , Kawai C. , Yui Y.
Published: December 2017

It has been known that cytotoxic-activated macrophages release an unstable vasorelaxing substance, nitric oxide. We have found that a more stable relaxing factor is released from those cells. This factor seems to be synthesized from L-arginine. It acts through the activation of soluble guanylate cyclase without affecting membrane potential. It has little charge at nearly neutral pH, and its molecular weight is < 500.
Mechanical perturbation of cultured human endothelial cells causes rapid increases of intracellular calcium
Authors: Sigurdson W. J. , Sachs F. , Diamond S. L.
Published: December 2017

In first-passage human umbilical vein endothelial cells (HUVEC) and bovine aortic endothelial cells (passages 13–16), exposure to gentle mechanical perturbation using a micropipette caused a transient rise in intracellular calcium concentration ([Ca2+]i). The increase in calcium concentration ([Ca2+]) occurred each time the cell was nudged. Three responses were evoked in each of 27 cells using 5 independent HUVEC harvests. Increase in [Ca2+] returned to near baseline levels within approximately 30 s. The stimulus did not cause membrane puncture, as indicated by 1) absence of rapid dye leakage, 2) regulated nature of the [Ca2+] response, 3) absence of membrane blebbing, and 4) repeatable nature of the response in the same cell. As an alternative stimulus, we created very narrow fluid streams (1- to 2-microns diam) from a pressurized pipette that generated shear stresses of approximately 0.001–0.1 dyn/cm2 on the cells. However, these low-shear streams had little effect on [Ca2+]i. The poke-induced change in [Ca2+] was not blocked by lowering extracellular [Ca2+] ([Ca2+]o; 10 microM). In the absence of [Ca2+]o, however, HUVEC did not respond to the first poke, indicating a requirement for some [Ca2+]o as a mediator of signaling. After several poke-induced responses, [Ca2+]i could still be released by caffeine (100 microM), indicating the integrity of the intracellular release mechanism(s). These studies indicate that the response of an endothelial cell to a membrane-deforming event involves a priming step utilizing [Ca2+]o, which facilitates the transient increase of [Ca2+]i.
Temperature dependence of oxygen diffusion and consumption in mammalian striated muscle
Authors: Bentley T. B. , Meng H. , Pittman R. N.
Published: December 2017

This study investigated the effect of temperature on the oxygen diffusion coefficient (DO2) of hamster retractor muscle from 11 to 37 degrees C. DO2 was measured using a non-steady-state technique, whereas muscle O2 consumption (VO2) was estimated after steady state was reached. DO2 was 0.84 +/- 0.04 x 10(-5) cm2/s at 11 degrees C and rose exponentially to 2.41 +/- 0.19 x 10(-5) cm2/s at 37 degrees C, producing a temperature coefficient for DO2 of 4.60%/degrees C for this temperature range. To measure DO2 directly at 37 degrees C, it was necessary to inhibit tissue VO2 with Amytal. The DO2 measurements made at 37 degrees C were significantly higher than previously reported values, which had been based on extrapolations from lower temperatures (6). Further analysis suggests a possible transition in the diffusion pathway between 23 and 30 degrees C, resulting in a DO2 higher than that previously expected. This larger DO2, together with a recently published value of oxygen solubility (alpha) (21), results in an in vitro Krogh's diffusion coefficient (KO2) that is 2.4 times larger than that previously reported (24) and therefore significantly reduces an order of magnitude discrepancy between in vitro and estimated in vivo KO2 values (24). Muscle VO2 was 0.35 ml O2.min-1.100 g-1 at 11 degrees C and increased with temperature, resulting in an activation energy of the rate-limiting reaction from the Arrhenius equation of -10.5 kcal/mol between 11 and 30 degrees C.
Thromboxane A2 analogue, U-46619, potentiates calcium-activated force in human umbilical artery
Authors: Crichton C. A. , Templeton A. G. , McGrath J. C. , Smith G. L.
Published: December 2017

It has previously been shown that human umbilical artery (HUA) smooth muscle produces thromboxane A2 in response to increasing oxygen levels and that this thromboxane promotes contraction. To investigate the intracellular action of thromboxane A2, strips of HUA longitudinal smooth muscle were permeabilized using alpha-toxin from the bacterium Staphylococcus aureus. This treatment rendered the surface membrane permeable to low-molecular-weight substances but left functional thromboxane A2 receptors. Tension measurements were used to investigate the effect of the stable thromboxane A2 analogue, U-46619, on the Ca2+ sensitivity of smooth muscle contractile proteins. U-46619 (1 nM to 1 microM) potentiated submaximal Ca(2+)-activated force (generated by [Ca2+], 50 nM to 3 microM) but not maximal Ca(2+)-activated force (generated by [Ca2+], 10–100 microM). The specific thromboxane A2 receptor antagonist, GR-32191B (1 microM), inhibited the action of U-46619 (0.1 microM). The potentiation of submaximal Ca(2+)-activated force produced by the muscle in response to U-46619 (0.1 microM) was antagonized by guanosine 5'-O-(2-thiodiphosphate) (1 mM), the nonhydrolyzable analogue of GDP, and mimicked by guanosine 5'-O-(3-thiotriphosphate) (100 microM), the nonhydrolyzable analogue of GTP. These results suggest that U-46619 acts via the previously identified thromboxane A2 receptor to promote Ca2+ sensitivity of tension production in HUA smooth muscle. Furthermore, this effect appears to be mediated via a G protein.
Effect of lidocaine on contracture, intracellular sodium, and pH in ischemic rat hearts
Authors: Butwell N. B. , Ramasamy R. , Lazar I. , Sherry A. D. , Malloy C. R.
Published: December 2017

The relationships among intracellular Na concentration ([Na+]i), intracellular pH, [ATP], and contracture during global ischemia were studied in isolated, perfused rat hearts. Intracellular Na was monitored by 23Na nuclear magnetic resonance (NMR) spectroscopy using thulium 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetra(methylene phosphonate) (TmDOTP5-) as the paramagnetic shift reagent. High-energy phosphates and pH were monitored under the same conditions using 31P-NMR spectroscopy. Lidocaine (130 microM), a class IB fast Na channel blocker known to protect ischemic myocardium, prolonged the time to contracture in both unpaced and paced hearts (240 beats/min). After 10 min of global ischemia in paced hearts, [Na+]i was lower in the lidocaine-treated group compared with untreated hearts. The addition of lidocaine also significantly attenuated the depletion of ATP as well as development of intracellular acidosis. At the time of contracture, however, there was no difference in [Na+]i or pH between the two groups. Interestingly, the effect of lidocaine on Na+i accumulation during ischemia was manifested during the first 5–10 min of ischemia, while its effect on pH occurred after 9 min. This finding suggests that a mechanism other than the Na-H exchanger may play a role in the accumulation of Na+i early in the course of ischemia.
Aging increases venous compliance in awake instrumented rats
Authors: Glick M. R. , Gehman J. D. , Gascho J. A.
Published: December 2017

To determine the effects of aging on total venous compliance, mean circulatory filling pressure (MCFP) was determined at several different blood volumes in 10 young (10-mo-old) and 10 older (30-mo-old) awake instrumented male Fischer 344/Brown Norway hybrid rats. Baseline weight and mean arterial pressure were similar in the two groups; heart rate was higher in the young (426 +/- 9 beats/min) than in the older rats (376 +/- 8 beats/min). Although MCFP was similar in the two groups at baseline blood volume, MCFP rose less with transient volume expansion and fell less with transient volume depletion in the older rats. The calculated venous compliance (reciprocal of the slope of the MCFP-to-volume relation) for the older rats was 25% greater than in the younger rats (3.28 +/- 0.21 vs. 2.63 +/- 0.12 ml.kg-1.mmHg-1; P = 0.014). In this conscious instrumented rat model, baseline total venous compliance is increased in older rats.
Alternative splicing of CFTR Cl- channels in heart
Authors: Horowitz B. , Tsung S. S. , Hart P. , Levesque P. C. , Hume J. R.
Published: December 2017

We have previously demonstrated that cystic fibrosis transmembrane conductance regulator (CFTR) Cl- channels are expressed in heart (Levesque et al., Circ. Res. 71: 1002–1007, 1992). However, the structural identity between this cardiac protein and CFTR in epithelial cells is unknown. We amplified cDNA from rabbit ventricle and cloned fragments corresponding to the 12 transmembrane spanning domains of the epithelial CFTR transcript. The deduced sequence from rabbit heart indicated deletion of a 30-amino acid segment in the first cytoplasmic loop of CFTR, which corresponds to known locations of intron-exon junctions bordering exon 5 in the CFTR gene, suggesting that CFTR is alternatively spliced in heart. Outside this region, the heart CFTR isoform displayed > 95% identity to human epithelial CFTR. Molecular analysis demonstrated CFTR expression only in cardiac tissues that exhibited a adenosine 3',5'-cyclic monophosphate-dependent Cl- conductance in native cells. The expression of a specific isoform of CFTR Cl- channels in mammalian heart may have functional and clinical significance.
Ontogeny of Big endothelin-1 effects in newborn piglet pulmonary vasculature
Authors: Liben S. , Stewart D. J. , De Marte J. , Perreault T.
Published: December 2017

Endothelin-1 (ET-1), a 21-amino acid peptide produced by endothelial cells, results from the cleavage of preproendothelin, generating Big ET-1, which is then cleaved by the ET-converting enzyme (ECE) to form ET-1. Big ET-1, like ET-1, is released by endothelial cells. Big ET-1 is equipotent to ET-1 in vivo, whereas its vasoactive effects are less in vitro. It has been suggested that the effects of Big ET-1 depend on its conversion to ET-1. ET-1 has potent vasoactive effects in the newborn pig pulmonary circulation, however, the effects of Big ET-1 remain unknown. Therefore, we studied the effects of Big ET-1 in isolated perfused lungs from 1- and 7-day-old piglets using the ECE inhibitor, phosphoramidon, and the ETA receptor antagonist, BQ-123Na. The rate of conversion of Big ET-1 to ET-1 was measured using radioimmunoassay. ET-1 (10(-13) to 10(-8) M) produced an initial vasodilation, followed by a dose-dependent potent vasoconstriction (P < 0.001), which was equal at both ages. Big ET-1 (10(-11) to 10(-8) M) also produced a dose-dependent vasoconstriction (P < 0.001). The constrictor effects of Big ET-1 and ET-1 were similar in the 1-day-old, whereas in the 7-day-old, the constrictor effect of Big ET-1 was less than that of ET-1 (P < 0.017).(ABSTRACT TRUNCATED AT 250 WORDS)
5-Hydroxytryptamine dominates over thromboxane A2 in reducing collateral blood flow by activated platelets
Authors: Loots W. , De Clerck F.
Published: December 2017

Intra-aortic infusion of collagen (100 micrograms/kg in 1 min) elicited an extensive platelet activation and transient but marked reductions of blood flow and increases of peripheral vascular resistance, both responses being more pronounced in collaterals than in normal arterial beds in feline hind legs. Blockade of 5-hydroxytryptamine (5-HT) subtype 2 (5-HT2) receptors for 5-HT (ketanserin or ritanserin, 0.63 mg/kg iv, -10 min) or amine depletion (reserpine, 0.1 mg/kg im, -10 days, + parachlorophenylalanine 100 mg/kg sc daily for 3 days), but not cyclooxygenase inhibition (indomethacin, 5 mg/kg iv) or thromboxane (Tx) A2/prostaglandin endoperoxide receptor antagonism (sulotroban, 2.5 mg/kg iv), largely prevented the collagen-induced perfusion defect without interfering substantially with the platelet activation process. TxA2 synthase inhibition, alone (dazoxiben, 5 mg/kg iv) or combined with TxA2-prostaglandin endoperoxide receptor antagonism (ridogrel, 2.5 mg/kg iv), partially reduced the collagen-induced perfusion defect and limited to a similar extent the initial platelet aggregation and release of 5-hydroxyindoles and TxB2 while increasing plasma levels of prostacyclin. These results suggest that platelet-derived 5-HT dominates over TxA2 in reducing blood flow in collateral-dependent tissue of the cat hindlimb.
Dependence of endothelium-mediated relaxation on oxygen and metabolism in porcine coronary arteries
Authors: Hashimoto M. , Close L. A. , Ishida Y. , Paul R. J.
Published: December 2017

Hypoxia has major effects on endothelium-dependent relaxation. To further understand the underlying mechanism(s), we investigated the O2 dependence of the endothelium-dependent relaxations elicited by ionophore A-23187 or agonists substance P (SP) or thrombin (TB) in porcine coronary arteries. A-23187 elicits an endothelium-dependent relaxation of KCl- or U-46619-induced contractures that can be described in terms of a rapid and slow phase. The duration of the relaxation was dose dependent. SP (10 nM) and TB (0.1 U/ml) also elicited endothelium-dependent relaxations that were rapid but transient. Hypoxic conditions (95% N2-5% CO2 instead of 95% O2-5% CO2; PO2 < 1%) abolished the A-23187 rapid phase and the SP and TB transient relaxation but not the A-23187 slow phase. Threshold PO2 for the rapid phase was approximately 35 mmHg. Pretreatment with cyanide (5 mM), to inhibit respiration, or 2-deoxy-D-glucose, to inhibit glycolysis, had little effect. Similarly, propranolol (10 microM) or indomethacin (10 microM) had no effect on the relaxation to A-23187, TB, or SP. In contrast, both NO synthesis inhibitors and ouabain blunted all endothelium-dependent relaxations studied. Our results suggest that the rapid relaxations to A-23187, SP, and TB are sensitive to O2 but not mitochondrial respiration. The slow sustained relaxation induced by A-23187, however, is characterized by a sensitivity to O2 that is distinct from that of the rapid phase, yet is dependent on an intact endothelium and is affected by NO synthesis inhibitors. Thus the endothelium-dependent relaxation to A-23187 is probably mediated by NO, but its sensitivity to O2 suggests that two distinct mechanisms may be involved.
Age-dependent overflow of endogenous norepinephrine from paraventricular hypothalamic nucleus of hypertensive rats
Authors: Qualy J. M. , Westfall T. C.
Published: December 2017

The relationship between age and central noradrenergic neuronal activity of the paraventricular hypothalamic nucleus (PVH) was examined in 7- to 10-, 12- to 14-, and 30- to 36-wk-old Sprague-Dawley (SD), Wistar-Kyoto (WKY), and spontaneously hypertensive rats (SHR). As an index of noradrenergic activity, endogenous norepinephrine (NE) overflow was assessed utilizing a miniaturized push-pull cannula assembly in unanesthetized freely moving rats. NE overlow under basal, 56 mM K+ stimulation, and in response to pressor/depressor drugs, were examined in all three strains at all ages. Significant increases in basal and K(+)-stimulated overflow of endogenous NE from the PVH were observed in all ages of SHR compared with normotensive controls with the greatest percent increase occurring during the development of hypertension in SHR. In addition, a reciprocal relationship exists with respect to blood pressure and overflow of NE from the PVH such that increases/decreases in blood pressure elicit decreases/increases in NE overflow in all strains at all ages examined. However, developing hypertensive SHR exhibited attenuated decreases in overflow of NE from the PVH compared with age-matched controls and established hypertensive SHR. These results suggest that noradrenergic pathways of the PVH contribute to the development and maintenance of arterial pressure hemostasis and that enhanced central noradrenergic neuronal activity is greatest during the development of hypertension in SHR.