bluuebunny/crossref_metadata_2025 huggingface dataset:
Agents that modify EDRF formation alter antiplatelet properties of brain arteriolar endothelium in vivo
Authors: Nishimura H. , Rosenblum W. I. , Nelson G. H. , Boynton S.
Published: December 2017

In the presence of circulating Evans blue a helium-neon laser injures the endothelium of brain surface arterioles in situ. The injury is known to selectively eliminate endothelium-dependent responses. The present study documents in mice the fact that such endothelial sites become selectively attractive to passing platelets that have been activated as a result of more severe injury upstream. We then test the hypothesis that the “capture” of platelets at the downstream site is due to loss of “classical” endothelial-dependent relaxing factor of acetylcholine (EDRFACh) at that site. EDRFACh is known to inhibit platelet adhesion/aggregation and is synthesized from L-arginine. We show that agents that would either enhance or reduce the synthesis of local EDRFACh reduce or increase the incidence of capture as predicted by the hypothesis. Thus NG-monomethyl-L-arginine (L-NMMA) and arginase that would reduce synthesis of EDRFACh enhanced platelet capture. L-Arginine, which would enhance synthesis of EDRFACh, inhibited platelet capture. In addition, L-NMMA and arginase enhanced platelet aggregation over the more severely damaged site upstream from the site of capture. Ex vivo studies of platelets harvested from treated mice showed that the platelets themselves were unaffected by the treatments that, except for arginase given intravenously, all involved topical application of the tested drugs.
Sensitivities of cardiac O2 consumption and contractility to catecholamines in dogs
Authors: Ohgoshi Y. , Goto Y. , Futaki S. , Yaku H. , Suga H.
Published: December 2017

We studied the effects of plasma catecholamines from the adrenal gland on systolic pressure-volume area (PVA)-independent O2 consumption (VO2) and contractility index (Emax) in the left ventricle of excised cross-circulated dog hearts. PVA is a measure of the total mechanical energy of contraction. Under baseline conditions, the PVA-independent VO2 correlated with plasma catecholamine level in the hearts (r = 0.84). Plasma epinephrine and norepinephrine levels increased gradually from 0.3 and 0.4 ng/ml to 10.3 and 2.7 ng/ml on average during adrenal sympathetic nerve stimulation of support dogs. Simultaneously, Emax and PVA-independent VO2 increased by 240 +/- 127 (SD) and 75 +/- 24%. Although their increases were monotonic in a given heart, their sensitivities to catecholamines were considerably variable among hearts. However, these two sensitivities were correlated (r = 0.96) with each other in the hearts, and the interheart variation of the sensitivity of the PVA-independent VO2 to Emax (i.e., oxygen cost of Emax) was smaller. We conclude that the oxygen cost of Emax is less variable among hearts despite large interheart variations of Emax and VO2 responses to plasma catecholamines.
Microvascular permeability transients due to histamine in cat limb
Authors: Wolf M. B. , Scott D. R. , Watson P. D.
Published: December 2017

We measured the protein solvent drag reflection coefficient (sigma f) and the capillary filtration coefficient (CFC) before and after adding 1 or 10 microM histamine to the recirculating fluid (20% plasma, remainder albumin and electrolytes, hematocrit of 1-2%) perfusing the isolated cat hindlimb preparation. Transient sigma f measurements were made at 3- to 15-min intervals after histamine using a modification of the steady-state integral-mass balance method. CFC measurements were made at approximately 10-min intervals after histamine in separate experiments. A 1 microM dose of histamine caused sigma f to fall from approximately 0.8 to approximately 0.3 in 2-3 min; sigma f then returned to control in approximately 20 min. CFC response to the 1 microM histamine was a peak increase approximately 2 times control and a return to control in approximately 40 min. A 10 microM dose caused sigma f to fall rapidly to near zero. In general, recovery was much slower than for the 1 microM dose, most of the limbs not returning to control by 40 min after histamine. CFC measurements after 10 microM histamine increased only approximately 5 times control even though sigma f was near zero at the same time. CFC remained above control for approximately 60 min. The combined sigma f and CFC data could be described quantitatively if histamine simultaneously opened both short-lived large gaps (approximately 1,000 A) and a longer-lived pathway that sieved protein like the normal pathway and if the numbers of channels of each pathway closed exponentially with 4- and 15-min time constants, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)
LTD4 and bradykinin evoke endothelium-dependent relaxation of the renal vein: dissimilar mechanisms
Authors: Pawloski J. R. , Chapnick B. M.
Published: December 2017

This study's goals were to define the vasomotor effects of the peptide leukotriene (LT)D4 on norepinephrine (NE)-contracted isolated rings of canine renal vein (RV) and to compare these influences with those of bradykinin (BK). Canine RV rings were connected to isometric force transducers and bathed in Krebs-Ringer bicarbonate buffer containing indomethacin (10-5M). LTD4 and BK evoked dose-dependent decreases in tone of NE-contracted RV rings that were abolished by physical removal of the endothelium. Relaxation of the RV ring produced by glyceryl trinitrate (GTN) was slightly enhanced or unaltered after endothelium denudation. Reduced human hemoglobin (Hb, 10(-6) M), NG-monomethyl-L-arginine (L-NMMA, 300 microM) and methylene blue (MB, 10(-6) M) had no effect on LTD4-induced venomotor relaxation, whereas they significantly decreased the vasorelaxant effect of BK. In contrast, endothelium-dependent relaxation of renal arterial rings produced in response to both LTD4 and BK was markedly attenuated in the presence of either reduced Hb (10(-6)M) or MB (10(-6) M). MB significantly attenuated venorelaxant responses to GTN (10(-8) to 10(-6) M). The ATP-sensitive K(+)-channel blocker glybenclamide (10(-6)M) inhibited relaxation of the RV induced by cromakalim (5 x 10(-8)M) but had no effect on LTD4-evoked relaxation. These data indicate that endothelium-dependent relaxation of the RV elicited by BK is dependent on “classic” endothelium-derived relaxing factor (EDRF) considered to be nitric oxide (NO) or an unstable nitroso compound that ultimately liberates the NO radical.(ABSTRACT TRUNCATED AT 250 WORDS)
Quantitation of dynamic AV nodal properties and application to predict rate-dependent AV conduction
Authors: Nayebpour M. , Talajic M. , Nattel S.
Published: December 2017

A number of functional properties of the atrioventricular (AV) node have been described in response to changes in the atrial input rate. The purpose of this study was 1) to develop quantitative descriptors of these properties, and 2) to determine whether they can account for rate-dependent changes in AV nodal conduction. The delay in AV nodal conduction of single premature beats (recovery) was found to be an exponential function of coupling interval with a time constant of 66 +/- 2 (+/- SE) ms. A single abbreviated (facilitation) cycle did not alter the time constant of recovery or basal conduction for a subsequent beat but shifted its recovery curve to the left to an extent exponentially related to the facilitation cycle length. The induction of a tachycardia with HA interval fixed so as to control the recovery and facilitation variables resulted in a first-order onset of AV conduction slowing (fatigue). The fatigue process had a time constant in the range of 70 beats and a magnitude that was a decaying exponential function of HA interval. An equation incorporating quantitative descriptors of recovery, facilitation, and fatigue accurately predicted rate-dependent changes in AH interval. We conclude that 1) the AV nodal properties of recovery, facilitation, and fatigue are amenable to quantitative characterization, and 2) rate-dependent changes in AV nodal conduction time can be well described in terms of these underlying properties.
Afferent vascular resistance control during hemorrhage in normal and autonomically blocked rabbits
Authors: Courneya C. A. , Korner P. I. , Oliver J. R. , Woods R. L.
Published: December 2017

We examined the role of the arterial and cardiac baroreceptors on the hindquarter conductance and heart rate responses of conscious rabbits bled at approximately 3% blood volume (BV)/min to 80% BV (i.e., 20% BV removed). We used rabbits with both sets of baroreceptors working and when only one or neither sets was working. Each animal was studied with normal effector function and during autonomic blockade (hormonal + local effectors), where release of arginine vasopressin (AVP) and renin (angiotensin II, ANG II) were enhanced. The local response (LR) to hemorrhage was determined in a separate group of neurohumorally blocked rabbits. The estimated constrictor response (ECR) was the difference between the LR and net conductance response. In normal rabbits, the ECR was 49 units, with the estimated arterial-to-cardiac barorecptor drive ratio approximately 2.8:1 and with the two receptor groups acting by simple addition. Both barorecptors contributed to the rise in heart rate, with the relative arterial-to-cardiac baroreceptor drive ratio approximately 4:1. When hemorrhage was performed during autonomic blockade, ECR was 84 units (compared with normal rabbits, P less than 0.01), but blood pressure was poorly maintained and the constrictor effect was not under baroreceptor control. Although the baroreceptors were critical for AVP release during autonomic blockade, they played no role in renin release (ANG II production); the latter was released in large amounts, producing near-maximum constriction, which was unrelated to the afferent input. Thus neurally mediated regulation during hemorrhage has substantial advantages over that mediated primarily through the pressor hormones.
Differential effects of intra- and extraluminal endothelin on cerebral arterioles
Authors: Ogura K. , Takayasu M. , Dacey R. G.
Published: December 2017

The differential effects of intraluminal and extraluminal application of endothelin, the endothelium-derived constricting factor, were studied in isolated intracerebral arterioles that were cannulated and perfused in vitro. Extraluminal and intraluminal application of 10(-8) M endothelin constricted the arterioles to 38.2 +/- 6.7 and 75.1 +/- 5.7% of the control diameter, respectively. Constrictions induced by either the intraluminal or the extraluminal application of endothelin were inhibited in a Ca(2+)-free solution. Nimodipine attenuated, but did not completely abolish, the constriction induced by the extraluminal application of endothelin, but it did abolish the constriction induced by the intraluminal application. The duration of vasoconstriction also differed between intra- and extraluminal application. Vessel diameter quickly returned to the control value as soon as intraluminal perfusion of endothelin was terminated. In contrast, the constriction induced by extraluminal application of endothelin lasted much longer and was difficult to reverse. The differential effect of intraluminal and extraluminal endothelin application appears to reflect the important barrier-function of the cerebrovascular endothelium of intracerebral arterioles.
ATP-sensitive K+ channels from aortic smooth muscle incorporated into planar lipid bilayers
Authors: Kovacs R. J. , Nelson M. T.
Published: December 2017

Glibenclamide binding sites were identified in a membrane preparation from canine aortic smooth muscle. The dissociation constant for [3H]glibenclamide binding was 10 +/- 2 nM, with a density of 420 +/- 108 fmol/mg protein. The properties of ATP-sensitive potassium (KATP) channels from the same membrane preparation incorporated into planar lipid bilayers were investigated. ATP was a potent inhibitor of the channels with half-maximal inhibition of channel activity by 41 microM ATP. Glibenclamide inhibited channel activity, and cromakalim activated the channel in the presence of ATP. Blockers of Ca(2+)-activated K+ (KCa) channels (charybdotoxin and tetraethylammonium ions) did not affect KATP channels in concentrations that caused significant block of KCa channels in bilayers. This membrane preparation should allow further biochemical and functional characterization of KATP channels and glibenclamide receptors in arterial smooth muscle.
Does pentobarbital anesthesia depress left ventricular contractility in dogs?
Authors: Unruh H. W. , Wang R. , Bose D. , Mink S. N.
Published: December 2017

Although pentobarbital sodium (NP) anesthesia has been shown to depress left ventricular (LV) contractility in dogs, measurements of LV contractility in previous studies have been made soon after a bolus of NP was given when serum concentrations would be extremely high. In this study, we compared indexes of LV contractility during awake and anesthetized conditions. During anesthesia, measurements were obtained 1 h after an intravenous bolus of NP was given when serum concentrations were approximately 25 mg/l and above that reported to abolish pain. In 13 dogs, subendocardial ultrasonic crystal transducers and a high-fidelity pressure transducer were implanted into the LV. Measurements were obtained with and without prior treatment with propranolol to produce beta-adrenergic blockade. LV contractility was assessed by ejection fraction and the end-systolic pressure-volume relationship. The effect of NP on ventricular myocardium was also examined in an in vitro canine right trabecular preparation to compare in vivo and in vitro effects. In the in vivo study, the results showed no decrease in LV contractility during anesthesia regardless of whether propranolol was administered. The in vitro preparation showed only a minimal decrease in isometric tension at the concentrations used in the in vivo study. We conclude that NP anesthesia does not depress LV contractility when concentrations are maintained at approximately 25 mg/l.
Volumetric response of right ventricle during progressive supine exercise in men
Authors: Mols P. , Huynh C. H. , Naeije N. , Ham H. R.
Published: December 2017

Right ventricular (RV) adaptation to supine exercise has been studied in 10 young male volunteers by 81mKr electrocardiogram (ECG)-gated radionuclide ventriculography. During progressive supine exercise, the ejection fraction gradually increased from a mean value of 46% at rest up to 60% at a maximal exercise level. End-diastolic volume however remained unchanged at a low exercise level and even slightly decreased at a higher exercise level. Little or no change in end-diastolic volume and an increase in ejection fraction produced a significant decrease in end-systolic volume and a net increase in stroke volume. These results indicate that the Frank-Starling mechanism does not contribute to the increase in right ventricular stroke volume during progressive supine exercise, but the increase in right ventricular stroke volume rather seems related to an increased contractility, presumably mediated by an increased sympathetic activity.
Peripheral circulatory control of cardiac output in diabetic rats
Authors: Litwin S. E. , Raya T. E. , Daugherty S. , Goldman S.
Published: December 2017

Diabetes is believed to be associated with impaired systolic and diastolic function of the heart; however, some investigators have found that diabetic rats have increased cardiac output. We investigated changes in the peripheral circulation that could account for an increased cardiac output in diabetic rats (n = 30), 4 wk after a single tail vein injection of streptozotocin (60 mg/kg), and age-matched control rats (n = 31). Compared with controls, diabetic rats exhibited decreased (P less than 0.05) mean arterial pressure, characteristic aortic impedence, and total peripheral resistance; however, cardiac index and stroke volume index were increased. Aortic compliance, mean circulatory filling pressure, central venous pressure, pressure gradient for venous return, and venous compliance were unchanged in the diabetic rats compared with control. Baseline left ventricular end-diastolic pressure and end-diastolic volume were increased in the diabetic rats. Following a volume load of 30 ml/kg, cardiac index and stroke volume index increased less in the diabetic than in the control rats (35 vs. 102% and 69 vs. 105%, respectively). Thus, even with impaired systolic function, cardiac output is increased or maintained in diabetic rats because of the combination of decreased afterload and maintenance of preload.
Effects of paraventricular nucleus lesions on chronic renal hypertension
Authors: Herzig T. C. , Buchholz R. A. , Haywood J. R.
Published: December 2017

The contribution of the paraventricular nucleus region of the hypothalamus (PVN) to the maintenance of one-kidney, figure-8 renal wrap hypertension was determined in this study. Electrolytic ablation of the PVN was performed 4 wk after the production of hypertension or sham operation. Ablation of the PVN region significantly reduced mean arterial pressure (MAP) from 150 +/- 9 to 110 +/- 3 mmHg in the hypertensive rats. In the sham-hypertensive group, the lesion decreased MAP from 118 +/- 2 to 99 +/- 4 mmHg. In both groups of animals MAP from 118 +/- 2 to 99 +/- 4 mmHg. In both groups of animals MAP returned to prelesion values by day 7 postlesion. When ganglionic blockade was performed on day 7 postlesion, the fall in MAP was greater in hypertensive rats (-44 +/- 5 mmHg) than in normotensive rats (-26 +/- 3 mmHg). In a separate group of rats studied 3 days after PVN ablation, ganglionic blockade produced similar decreases in MAP in the wrapped and sham-operated animals. These studies suggest that the PVN contributes to the increased functional sympathetic nervous system associated with one-kidney, figure-8 renal hypertension. Although ablation of the PVN region decreases MAP, neural mechanisms compensate to return MAP to hypertensive levels.
Two types of G proteins involved in regulation of phosphoinositide turnover in pulmonary endothelial cells
Authors: Tkachuk V. A. , Voyno-Yasenetskaya T. A.
Published: December 2017

The involvement of G proteins in hormonal regulation of phospholipase C in bovine pulmonary arterial endothelial cells and human umbilical vein endothelial cells has been investigated. Histamine and bradykinin stimulated phosphoinositol (PI) turnover in a dose-dependent manner, and phorbol-myristate-acetate inhibited hormone-dependent activation of PI turnover, indicating a feedback control of this process. Activation of PI turnover by histamine and bradykinin is guanine nucleotide-dependent. Stimulation of the endothelial cell G proteins by guanosine 5'-0-(3-thiotriphosphate) leads to the potentiation of hormone-induced activation of PI turnover, whereas guanosine 5'-0-(2-thiodiphosphate), which inactivates G proteins, blocks the hormone-dependent PI turnover. Pertussis toxin blocked the histamine-dependent stimulation but did not affect the bradykinin-dependent stimulation of phospholipase C. By contrast, botulinurn toxin (C2 + C3 components) blocked the bradykinin-dependent stimulation of phospholipase C but did not affect the histamine-dependent stimulation of this enzyme. These data suggest that at least two different G proteins are involved in hormone-dependent stimulation of phospholipase C in endothelial cells.

bacterial toxins; hormone regulation; phospholipase C
Targeting of macromolecular carriers and liposomes by antibodies to myosin heavy chain
Authors: Klibanov Alexander L. , Khaw Ban An , Nossiff Naseem , O'Donnell Sean M. , Huang Leaf , Slinkin Mikhail A. , Torchilin Vladimir P.
Published: December 2017

Macromolecular carriers and liposomes were covalently coupled to monoclonal antibodies against cardiac myosin heavy chain. Deferoxamine-modified polymers bound tightly with 67Ga and 68Ga radioisotopes. Ternary deferoxamine-polylysine antibody conjugates specifically targeted the radioisotopes to a myosin-coated microplate. Scatchard analysis revealed a high affinity of the conjugate for the target with a Kas of ≈108 M-1. Liposomes that contained immobilized antimyosin antibodies were targeted specifically to the myosin-coated plate. Additional coating of these liposomes with polyethylene glycol reduced specific binding to the target in vitro. However, because of the presence of polyethylene glycol on the surface of liposomes, these liposomes had a long half-life and slowly cleared from the bloodstream after intravenous injection. These immunoliposomes showed up to 16- to 18-fold specific localization to the necrotic areas of the myocardium in rabbits with experimental infarction.

antimyosin; chelating polymer; liposome; monoclonal antibody; myocardial infarction; radioimmunoimaging
Effects of free fatty acids and dichloroacetate on isolated working diabetic rat heart
Authors: Nicholl T. A. , Lopaschuk G. D. , McNeill J. H.
Published: December 2017

It is well established that cardiac dysfunction independent of atherosclerosis develops in both humans and animals with diabetes mellitus. The etiology is complex, involving many different processes, one of which may be increased fatty acid utilization and/or a concomitant decrease in glucose utilization by the diabetic heart. We compared control and 6-wk streptozotocin (STZ)-induced diabetic isolated working rat hearts and were able to demonstrate cardiac dysfunction in the diabetic as assessed by depressed heart rate (HR), heart rate peak systolic pressure product (HR.PSP), left ventricular developed pressure (LVDP), and rate of pressure rise (+dP/dt). Paralleling depressed cardiac function in the diabetic were hyperglycemia, hyperlipidemia, and decreased body weight gain compared with age-matched controls. The addition of free fatty acids, in the form of 1.2 mM palmitate, to the isolated working heart perfusate had no effect on either control or diabetic heart function, with the exception of a depressive effect on +dP/dt of diabetic hearts. But diabetic hearts perfused with palmitate-containing perfusate plus the glucose oxidation stimulator dichloroacetate (DCA) showed a marked improvement in function. HR and HR.PSP in spontaneously beating hearts, as well as LVDP and +dP/dt in paced hearts were all restored to control heart values in diabetic hearts perfused in the presence of DCA. Creatine phosphate and ATP levels were similar under all perfusion conditions, thus eliminating energy stores as the limiting factor in heart function. Results indicate that DCA will acutely reverse diabetic cardiac function depression. Therefore glucose oxidation depression in the diabetic heart may be a significant factor contributing to cardiac dysfunction.
Autoregulatory capacity in renal and mesenteric vasculatures of mineralocorticoid hypertensive dogs
Authors: Stoos B. A. , Metting P. J. , Britton S. L.
Published: December 2017

Experiments were performed in seven conscious dogs to quantitate the renal and mesenteric autoregulatory capacity in deoxycorticosterone acetate (DOCA)-salt hypertensive dogs. Each dog was chronically instrumented for the measurement of aortic blood pressure and blood flows through the superior mesenteric and left renal arteries (Doppler measurements); a right nephrectomy was also performed. To induce hypertension, animals were administered 5 mg/kg DOCA each day and given 1% saline as a drinking solution. After arterial pressure had increased by 25% (8-14 days of DOCA), a large-bore catheter was positioned retrograde in the left common carotid artery for subsequent connection to a gravity reservoir system for acute control of arterial pressure. Autoregulatory capacity was evaluated by controlling arterial pressure via the gravity reservoir at hypertensive and then normotensive values for 15-min periods. In neurally intact animals the renal, but not the mesenteric, circulation displayed autoregulatory capacity; the closed-loop gain of renal flow control averaged 0.92 +/- 0.06. Inhibition of autonomic ganglionic transmission (hexamethonium) increased the gain of flow regulation in the mesenteric circulation, but mesenteric autoregulation was not manifest. Ganglionic blockade, inhibition of prostaglandin formation, or blockade of histamine or adenosine receptors did not significantly influence renal autoregulatory capacity. These data demonstrate that the kidney has a high capacity to autoregulate in DOCA hypertension and suggest that autoregulatory-mediated renal vasoconstriction contributes to the increased total peripheral resistance.
Effects of oxidant stress on steady-state background currents in isolated ventricular myocytes
Authors: Matsuura H. , Shattock M. J.
Published: December 2017

Free radicals and oxidant stress have previously been shown to induce depolarization, transient action potential prolongation, and automaticity. We have investigated the ionic basis of these electrophysiological changes in isolated rabbit ventricular cells. Oxidant stress was generated by the photoactivation of rose bengal, and, in current-clamp experiments, the effects of oxidant stress on the action potential were confirmed. In voltage-clamp studies, oxidant stress decreased both inward and outward current through the inward-rectifier potassium channel, and the slope conductance (measured at the voltage-axis intercept near the resting membrane potential) was decreased from 40 +/- 8 to 25 +/- 6 nS (n = 6). Transient inward currents were induced on repolarization after a depolarizing clamp step, suggesting that the cells were calcium overloaded. In addition, oxidant stress activated a steady-state membrane conductance that showed a slight outward-going rectification and a reversal potential of approximately 0 mV. Evidence is presented to indicate that this reflects an increase in the conductance of the calcium-activated nonselective cation channel. The slope conductance of this calcium-activated channel (measured at the voltage-axis intercept) increased with prolonged exposure to oxidant stress (from 0.5 to 12 nS after 7 min), indicating that the intracellular free calcium increased gradually during the maintained application of rose bengal. These results suggest that oxidant stress depolarizes the cell membrane by reducing the inward-rectifier potassium current and by activating a calcium-activated membrane conductance. Both factors may contribute to the oxidant stress-induced changes in action potential duration and automaticity.
Effect of vasopressin on systemic capacity
Authors: Welt F. G. , Rutlen D. L.
Published: December 2017

To assess the effect of vasopressin (VP) on systemic capacity (SC), blood was drained from the venae cavae to an oxygenator and returned to the aorta at a constant rate so that changes in SC could be measured as the inverse of changes in oxygenator volume in 17 anesthetized pigs. After 10 min of VP administration (1.1 U/min ia), mean arterial pressure increased from 67 +/- 2 to 144 +/- 7 mmHg (P less than 0.001). SC decreased promptly and reached a nadir of 110 +/- 32 ml (P less than 0.02, 5.5 ml/kg) below control at 5 min but returned to 35 +/- 65 ml (P = not significant, 1.8 ml/kg) below control at 10 min. Portal venous pressure decreased from 19.3 +/- 2.6 to 16.6 +/- 2.7 mmHg (P less than 0.001), and portal flow decreased from 828 +/- 68 to 458 +/- 92 ml/min (P less than 0.001). Transhepatic venous resistance increased. After evisceration, VP caused only an increase in SC. Thus VP causes an initial SC decrement due entirely to a decrease in splanchnic capacity. The decrease in splanchnic capacity must be caused, at least in part, by the decrease in gastrointestinal arterial inflow and subsequent decrease in portal venous pressure. These initial effects of VP on SC would be expected to enhance ventricular filling and cardiac output in the intact animal and could be important in the acute compensatory response to hemorrhage.
Norepinephrine clearance is increased during acute hypoxemia in humans
Authors: Leuenberger U. , Gleeson K. , Wroblewski K. , Prophet S. , Zelis R. , Zwillich C. , Sinoway L.
Published: December 2017

Acute hypoxemia leads to activation of the sympathetic nervous system (SNS), yet adrenergic vasoconstriction does not occur and venous plasma norepinephrine (NE) fails to rise as expected. To examine whether this dissociation between SNS tone and plasma NE is due to altered metabolism of NE, we measured arterial NE kinetics ([3H]NE infusion technique) and sympathetic nervous outflow to muscle (peroneal microneurography) during 25-30 min of hypoxemia (spontaneous breathing, mean O2 saturation 74%) in six healthy young men. During hypoxemia, muscle sympathetic nervous activity (MSNA) rose significantly from 12.2 +/- 3.3 to 18.6 +/- 3.5 bursts/min, and the total amplitude increased from 123 +/- 36 to 255 +/- 50 mm/min. NE spillover, an index of NE release at the sympathetic nerve terminals, rose from 1.66 +/- 0.30 to 2.33 +/- 0.40 nmol.min-1.m-2 (P = 0.014). However, NE clearance increased also from 0.99 +/- 0.05 to 1.19 +/- 0.11 l.min-1.m-2 (P = 0.014), and arterial NE rose from 281 +/- 50 to 339 +/- 64 pg/ml (P = 0.023). Hypoxemia resulted in a significant rise in forearm blood flow and a decrease in forearm vascular resistance. The fact that skin blood flow and vascular resistance did not change implies that forearm vasodilation was localized to skeletal muscle. Our results suggest that during acute hypoxemia in humans the SNS is activated but the rise in plasma NE is attenuated because NE clearance is increased.
Kappa-opioid peptide receptor stimulation increases cytosolic pH and myofilament responsiveness to Ca2+ in cardiac myocytes
Authors: Ventura C. , Capogrossi M. C. , Spurgeon H. A. , Lakatta E. G.
Published: December 2017

Although kappa- and delta-opioid receptors on mammalian cardiac myocytes have been discovered recently, the intracellular effects that result from stimulation of these receptors remain unknown. We examine the effects of a rapid and brief exposure to a kappa-opioid receptor agonist on intracellular Ca2+, pH, and cell length in individual isolated rat ventricular cells. The specific kappa-agonist trans-dl-3,4-dichloro-N-methyl-N-[2-(1-pyrrolidinyl)cyclohexyl]- benzene-acetamide (U-50488H) (methane sulfonate salt) caused a transient increase in cytosolic pH (pHi) measured from the change in SNARF-1 fluorescence and an increase in cytosolic [Ca2+] (Cai), indexed by a change in indo-1 fluorescence. The initial Cai increase often was followed by Cai oscillations. Both pHi and Cai effects were blocked by the specific antagonist kappa-opioid receptor l-(N-furylmethyl)-alpha-normetazocine methane-sulfonate (Mr 1452). The amplitude of contraction that accompanied the Cai increase elicited by U-50488H was greater than that associated with a similar increase in Cai elicited by electrical stimulation or by the rapid exposure of cells to caffeine. Thus an acute and brief kappa-opioid receptor stimulation of cardiac cells leads to an increase in Cai and pHi. The pHi increase was abolished by 1) blockade of the Na(+)-H+ exchanger by ethyl isopropyl amiloride and 2) inhibition of protein kinase C (PKC) activity via pretreatment with staurosporine or prolonged incubation with 4 beta-phorbol 12-myristate 13-acetate. These maneuvers did not abolish the U-50488H-induced increase in Ca.(ABSTRACT TRUNCATED AT 250 WORDS)
Effects of hydroxyl radicals on ATPase and protein structure of myofibrils from rat heart
Authors: Robert V. , Ayoub S. , Berson G.
Published: December 2017

Free oxygenated radicals frequently are involved in cardiac arrhythmias and contractility disorders during postischemic reperfusion. The aim of this study was to determine the effects of hydroxyl radicals (.OH) in vitro on myofibrillar Ca-adenosinetriphosphatase (ATPase), on the redox state of thiol groups and the electrophoretic pattern of myofibrillar proteins from rat heart. Myofibrils were treated up to 60 min by .OH generated with 0.3 mM H2O2 and 0.1 mM Fe2+. After a 60-min treatment with .OH, the measurement of thiol groups failed to show any oxidation. On the contrary, ATPase activity and electrophoretic pattern were affected dramatically by treatment with .OH. For all Ca2+ concentrations, ATPase was increased after treatment with .OH, but ATPase activation when Ca2+ rose from pCa 8 to pCa 4.5 was only 92% after 30 min of incubation rather than 226% for untreated myofibrils. The electrophoretic analysis of myofibrillar proteins showed a decrease in myosin heavy chain and formation of aggregates in treated myofibrils. All of these effects were reduced when incubation was performed in the presence of mannitol, a specific scavenger of .OH. No effect was observed with 0.1 mM Fe2+ alone or with 0.3 mM H2O2. The action of .OH was very fast to the extent that the effects were observed after only 15 s of incubation. The results reported in the present study may be related to the impaired relaxation and contracture described in vivo within the first minutes of a postischemic reperfusion and before any change in calcium homeostasis.
Coronary artery narrowing in rats: mechanical alterations of left and right myocardium
Authors: Capasso J. M. , Li P. , Zhang X. , Anversa P.
Published: December 2017

To determine the effects of chronic coronary artery narrowing on myocardial contractile performance, nonocclusive constriction of the left coronary artery near its origin was surgically induced in rats and global cardiac hemodynamics, left and right myocardial mechanics, and the magnitude and distribution of tissue damage and interstitial fibrosis in the left ventricular wall were analyzed 1 mo later. Reductions in coronary artery luminal diameter of 55% resulted in left ventricular failure as characterized by decreases in systemic arterial pressures, systolic ventricular pressure, rise and decay in first derivative of left ventricular pressure (+/- dP/dt), and an increase in left ventricular end-diastolic pressure. Right side dysfunction was also present as documented by an elevation in right ventricular end-diastolic pressure and a reduction in -dP/dt. In vitro measurements of papillary muscle mechanics revealed a biventricular reduction in isometric developed tension and peak rates of tension rise and decay. Moreover, the kinetic parameters of isometric contraction duration, time to peak tension and time to one-half relaxation, were significantly shorter in left muscles from coronary artery-narrowed animals. Isotonically, peak muscle shortening was reduced in the left muscle, whereas time to peak shortening was prolonged in the right myocardium. In addition, the velocities of muscle shortening and relengthening were decreased in both ventricles. Foci of replacement fibrosis and diffuse interstitial fibrosis were found in the epimyocardium, midmyocardium, and endomyocardium, demonstrating that a significant amount of myocyte loss occurred throughout the left ventricular wall.(ABSTRACT TRUNCATED AT 250 WORDS)
Myocardial mechanics predict hemodynamic performance during normal function and alcohol-induced dysfunction in rats
Authors: Capasso J. M. , Li P. , Anversa P.
Published: December 2017

To determine whether mechanical evaluation of muscle tissue removed from the myocardium can be employed as a direct indicator of cardiac contractile performance in situ, isometric and isotonic parameters of muscle mechanics in vitro were correlated with in vivo global functional characteristics of the same heart. Twelve-month-old animals maintained on standard food and water were employed as representative of normal cardiac function. Animals of identical age with left ventricular (LV) dysfunction induced by oral alcohol (30%) ingestion from 4 to 12 mo were utilized to represent depressed cardiac performance. Accordingly, 24 h after the establishment of the hemodynamic profile for a control or experimental heart, the LV posterior papillary muscle was removed from the same heart and examined isometrically and isotonically. Least squares regression analysis was employed to establish a correlation coefficient and P values between various in vitro and in vivo parameters. Hemodynamic measurements were performed under chloral hydrate anesthesia and LV pump performance was evaluated with respect to aortic and ventricular pressures and the rates of rise and decay of the LV pressure trace. Papillary muscles were evaluated with respect to timing parameters of the isometric and isotonic twitch, the first derivative of isometric tension development, and the speed of muscle shortening at increasing physiologic loads. LV peak rate of pressure rise and decay were then correlated with the various isometric and isotonic properties. Myocardial mechanics and hemodynamics revealed depressed function in the papillary muscles and hearts from alcoholic rats. Moreover, significant correlations were found between the LV rate of pressure change (peak +dP/dt and -dP/dt) and both isometric and isotonic twitch measurements.(ABSTRACT TRUNCATED AT 250 WORDS)
EDRF-mediated shear-induced dilation opposes myogenic vasoconstriction in small rabbit arteries
Authors: Pohl U. , Herlan K. , Huang A. , Bassenge E.
Published: December 2017

In small saline-perfused rabbit mesenteric arteries (diam 221 +/- 4 microns, means +/- SE; n = 48) in situ, the interactions of endothelium-derived relaxing factor (EDRF)-mediated flow-dependent dilation and myogenic constriction were studied. When pump flow was increased two- to fivefold (2.8 +/- 0.1-fold), input perfusion pressure rose by 133 +/- 17%. Vessel diameter first increased passively by 9 +/- 1% and then decreased to or below control values reflecting the vascular myogenic activity. This was followed by a 16 +/- 3% increase in diameter, which was flow dependent, because nonperfused vessels exposed to the same intravascular pressures did not dilate. When the perfusate viscosity was increased with dextran solutions, both the basal diameters and the flow-induced dilator responses were significantly augmented, indicating that the increase in shear stress was the stimulus. The flow-dependent dilation was abolished by inhibition of EDRF with either hemoglobin (10 microM) or NG-nitro-L-arginine (0.3 mM) and also after preincubation with neuraminidase (0.2 U/ml, 30 min), which removes part of the membrane glycocalyx. Thus, myogenic responses in small mesenteric arteries can be effectively opposed by shear-induced release of EDRF. This might be a major mechanism for maintaining adequate tissue perfusion when pressure and shear stress increase simultaneously (e.g., exercise hyperemia, autoregulation) and otherwise myogenic activity would reduce vascular conductivity.
Measurement of regional glucose metabolic rates in reperfused myocardium
Authors: Buxton D. B. , Schelbert H. R.
Published: December 2017

Regional myocardial glucose utilization was measured with [18F]fluorodeoxyglucose (FDG) and positron emission tomography in normal and postischemic tissue after 3 h of intracoronary balloon occlusion in closed-chest chronically instrumented anesthetized dogs. Estimates of glucose metabolic rates were made using the Sokoloff model, assuming the lumped constant to be unchanged in reperfused tissue. Myocardial sectors were classified as normal, reversibly injured, or infarct containing based on occlusion blood flow images and postmortem histology. Occlusion flow, measured by microspheres, was reduced by 38% in reversibly injured and 74% in infarct-containing sectors, recovering to 91 and 66%, respectively, 1 h postreperfusion. One month postreperfusion, flow was normal in reversibly injured sectors but remained depressed at 60% in infarct-containing sectors. Glucose utilization at baseline was homogeneous, averaging 0.8 mumol.g-1.min-1. After 3 h of reperfusion following occlusion of the left anterior descending coronary artery, regional glucose metabolic rate was increased 60% relative to baseline in normal myocardium but not in postischemic sectors, leading to an enhancement of FDG uptake in normal relative to postischemic myocardium. At 24 h postreperfusion, the glucose metabolic rate decreased in normal remote tissue to 46% of baseline levels, probably reflecting increased plasma free fatty acid levels, but was not significantly altered in reversibly injured myocardium, leading to enhanced FDG uptake in reversibly injured relative to normal myocardium. Subsequently, glucose metabolism in normal and postischemic sectors was not significantly different. Prolonged relative enhancement of glucose metabolic rate in postischemic tissue was found when the glucose metabolic rate in normal myocardium was low. Myocardial glucose utilization correlated with hg, the rate constant for FDG phosphorylation under all conditions (r = 0.88).
Ischemically sensitive abdominal visceral afferents: response to cyclooxygenase blockade
Authors: Longhurst J. C. , Rotto D. M. , Kaufman M. P. , Stahl G. L.
Published: December 2017

Ischemically sensitive abdominal visceral afferents are known to reflexly stimulate the cardiovascular system. These nerve endings respond to severe hypoxia as well as to exogenously administered bradykinin and prostaglandins such as PGI2, PGE, and PGF2 alpha. We have shown previously that these prostaglandins can sensitize some previously unresponsive afferents to respond to ischemia. To determine if endogenously produced prostaglandins contribute to the observed increase in activity during ischemia, we recorded activity of 6 A delta- and 23 C-fiber sympathetic afferents in anesthetized cats during 5 min of ischemia before and 15-30 min after intravenous administration of either indomethacin (5 mg/kg) or aspirin (50 mg/kg). Before cyclooxygenase inhibition, we noted repeatable increases of 1.44 +/- 0.22 and 1.44 +/- 0.36 impulses/s in the A delta- and C-fibers, respectively, in response to ischemia. After indomethacin or aspirin, these increases were significantly reduced (P less than 0.05) in both thinly myelinated and unmyelinated afferents (0.69 +/- 0.36 and 0.46 +/- 0.21 impulses/s, respectively). In a second protocol, we observed that the activity of six A delta- and seven C-fibers was significantly reduced by aspirin or indomethacin when a single period of ischemia preceded cyclooxygenase blockade. These data, in conjunction with our previous observations, indicate that prostaglandins significantly contribute to the increased afferent discharge activity associated with ischemia of the abdominal visceral region.
Oxygen radicals, enzymes, and fluid transport through pericardial interstitium
Authors: Zawieja D. C. , Garcia C. , Granger H. J.
Published: December 2017

The interstitium is the final link in the transportation of nutrients from the bloodstream to the individual cells of an organism. To assess interstitial fluid transport in normal and inflamed tissue, the hydration (H, ml H2O/g dry wt) and hydraulic conductivity (Kp, 10(-8) cm2.s-1.cmH2O-1) of bovine pericardial stroma were determined. The effect of enzymes and neutrophil-derived products of inflammation on the properties of the interstitial model were determined. Samples of the pericardium were exposed separately to trypsin, elastase, hyaluronidase, collagenase, superoxide radicals, and hydrogen peroxide. After exposure, the tissues were washed repeatedly in physiological saline and equilibrated in transport chambers heated to 37 degrees C and pressurized to 50 cmH2O. Fluid flow across the tissues was monitored. A section of tissue was removed and weighed. The tissue section was subsequently dried and reweighed. Tissue thickness, H, and Kp were calculated. H and Kp of the control tissues were 2.82 +/- 0.04 and 1.71 +/- 0.07, respectively. Hydration was significantly increased (22-38%) by exposure to trypsin, elastase, collagenase, and superoxide radicals. Kp increased significantly (30-1055%) in the groups treated with trypsin, hyaluronidase, collagenase, and superoxide radicals. The inflammatory mediators generally increased the hydration and/or the hydraulic conductivity of the model. These results indicate that neutrophil-derived products could be involved in the development of interstitial edema during the inflammatory process.
Mechanisms regulating neurohypophysial blood flow and function during isotonic volume expansion
Authors: Diringer M. N. , Wilson D. A. , Hanley D. F. , Wu K. C. , Ladenson P. W. , Traystman R. J.
Published: December 2017

Regional cerebral and neurohypophysial blood flow responses to isotonic extracellular fluid volume expansion were studied in pentobarbital-anesthetized dogs using radiolabeled microspheres. Measurements were made at baseline and after increasing pulmonary capillary wedge pressure by 8 +/- 2 mmHg. Plasma arginine vasopressin (AVP) decreased by 50%, and neural lobe blood flow (NLBF) decreased by 47%. Blood flow through median eminence and other brain regions was unchanged. We investigated potential mechanisms responsible for the NLBF changes. Following control vagotomy, AVP concentration increased during the first hour and then returned to control values for hours 2 and 3, whereas NLBF was unchanged for the first hour and fell after 2 and 3 h. Vagus section abolished the decrease in NLBF but not the AVP response to volume expansion. The contribution of left atrial and pulmonary baroreceptors to this response was tested by inflation of a balloon in the left atria to produce a 13 +/- 1 mmHg rise in atrial pressure. This led to a 20% reduction in NLBF, a 35% reduction in AVP concentration, and a 270% increase in plasma atrial natriuretic factor (ANF). However, ANF release does not account for the NLBF changes, since intravenous ANF infusion had no effect on NLBF or AVP concentration. These data suggest that the NLBF response to volume expansion is mediated by the vagus with input from multiple cardiopulmonary baroreceptors.
Ruthenium red selectively prevents Ins(1,4,5)P3-but not caffeine-gated calcium release in avian atrium
Authors: Vites A. M. , Pappano A. J.
Published: December 2017

We previously reported that inositol 1,4,5-trisphosphate [Ins(1,4,5)P3] and caffeine evoked contractures in saponin-permeabilized chick atria. The magnitude of contractures evoked by maximally effective concentrations of Ins(1,4,5)P3 were half those evoked by maximally effective concentrations of caffeine. In the present report, we tested the hypothesis that these two agents may act on distinct calcium-release mechanisms by comparing the effects of ryanodine, ruthenium red, and procaine on the responses to Ins(1,4,5)P3 and caffeine. We find that procaine inhibits both responses with similar mean inhibitory concentrations in the millimolar range. Nanomolar concentrations of ryanodine selectively potentiate the contractures induced by Ins(1,4,5)P3 but have no effect on those induced by caffeine. Micromolar concentrations of ryanodine inhibit responses to both Ins(1,4,5)P3 and caffeine in a use-dependent way. Ruthenium red prevents the response to Ins(1,4,5)P3 and potentiates that to caffeine, as if ruthenium red had enhanced calcium accumulation in the caffeine-sensitive pool(s). Because we found that caffeine prevented the subsequent response to Ins(1,4,5)P3, but Ins(1,4,5)P3 had no detectable effect on the caffeine-induced contracture, we conclude that Ins(1,4,5)P3 and caffeine act on pharmacologically distinct calcium-release mechanisms that may reside in the same sarcoplasmic reticulum compartment.