bluuebunny/crossref_metadata_2025 huggingface dataset:
Differences in the electrophysiological response of canine ventricular subendocardium and subepicardium to acetylcholine and isoproterenol. A direct effect of acetylcholine in ventricular myocardium.
Authors: Litovsky S H , Antzelevitch C
Published: June 2012

A prolongation of the ventricular effective refractory period in response to cholinergic agonists or vagal stimulation has been demonstrated in a number of in vivo animal models. However, exposure of isolated myocardial tissues obtained from these hearts to as much as 10(-4) M acetylcholine has been shown to produce essentially no change in action potential duration or effective refractory period. The discrepancy between the in vivo and in vitro findings generally has been explained on the basis of accentuated antagonism, whereby parasympathetic agonists exert their influence through antagonism of the effects of beta-adrenergic tone in vivo. The fact that acetylcholine exerts little if any direct effect on the electrical activity of ventricular myocardium, although well accepted, is based exclusively on studies performed using endocardial preparations. Our recent demonstration of major electrophysiological differences between canine ventricular endocardium and epicardium prompted us to examine the effects of acetylcholine and the role of accentuated antagonism in these two tissue types. Using standard microelectrode techniques, we show that acetylcholine (10(-7)-10(-5) M) has little if any effect in canine ventricular endocardium but a pronounced effect to either prolong or markedly abbreviate action potential duration and effective refractory period in epicardium. These effects of acetylcholine on epicardium are attended by an accentuation of the spike and dome morphology of the action potential, are readily reversed with atropine, fail to appear when epicardium is pretreated with the transient outward current blocker 4-aminopyridine, are accentuated in the presence of isoproterenol (10(-7) to 5 x 10(-6) M), and persist in the presence of propranolol. Isoproterenol-induced abbreviation of action potential duration and effective refractory period is also shown to be more pronounced in epicardium than in endocardium; equimolar concentrations of acetylcholine completely antagonize the effects of isoproterenol in endocardium and epicardium. We conclude that acetylcholine exerts important direct effects on the electrical response of canine ventricular myocardium, which are accentuated in the presence of beta-adrenergic agonists. Our findings suggest the differential response of epicardium and endocardium to acetylcholine is due to the presence of a transient outward current-mediated spike and dome morphology in the epicardial action potential. Finally, the data suggest that acetylcholine may exert antiarrhythmic as well as arrhythmogenic effects through its actions to alter conduction and refractoriness.
Effect of protein kinase C activation on sarcoplasmic reticulum function and apparent myofibrillar Ca2+ sensitivity in intact and skinned muscles from normal and diseased human myocardium.
Authors: Gwathmey J K , Hajjar R J
Published: June 2012

Protein kinase C regulates the activity of a diverse group of cellular proteins including membrane ion channel proteins. Although protein kinase C and its substrate protein have been identified in both membrane and cytosolic fractions in the heart, the physiological role of this kinase in the regulation of cardiac function remains unknown. We examined the physiological role of protein kinase C by stimulating its activity with 12-deoxyphorbol 13 isobutyrate 20 acetate (DPBA) in human trabeculae carneae. This resulted in decreased peak isometric twitch force and peak intracellular sarcoplasmic reticulum calcium release as detected with aequorin. Furthermore, in the presence of DPBA, steady-state force-[Ca2+] relations were shifted to higher intracellular calcium concentrations, and the Hill coefficient was reduced, indicating a decrease in responsiveness of the myofilaments to calcium and a change in cooperativity among thin filament proteins, respectively. Thus, DPBA affects not only intracellular calcium concentration, but myofilament calcium interactions as well. The effect of DPBA on Ca2+ activation probably reflects phosphorylation of thin-filament regulatory proteins by protein kinase C.
The mechanism of positive inotropy induced by adenosine triphosphate in rat heart.
Authors: Scamps F , Legssyer A , Mayoux E , Vassort G
Published: June 2012

When applied extracellularly in the micromolar range, ATP and related compounds induced a positive inotropy in the rat papillary muscle. This was also true in the rat auricle after pertussis toxin treatment. Then, in both tissues, ATP further increased the contraction after a maximal beta-adrenergic stimulation. The increase in contractile force could be related to the increase in the calcium current. The L-type calcium current was measured by whole-cell patch-clamp recording in single cells isolated from the rat ventricle after the sodium and potassium currents were inhibited by tetrodotoxin and cesium, respectively. When added alone, 10 microM ATP increased the calcium current by 60%. Adenosine 5'-O-(3-thiotriphosphate) was also able to increase calcium current. Adenosine was much less effective, and GTP, UTP, CTP, and ITP were without effect. A similar increase in calcium current was observed when ATP was added in addition to a maximal stimulation by a beta-adrenergic agonist or after internal perfusion with cyclic AMP. However, this increase was preceded by a transient decrease whose origin could not be attributed to a P1-purinergic agonistic effect of ATP. The transient decrease was not elicited by adenosine or in a magnesium-free HEPES solution and was not suppressed after pertussis toxin treatment. This effect appeared related to the variations in the holding current also observed upon ATP application. Together with vasodilation, ATP and adenine compounds induced positive inotropy. The latter effect could be attributed in part to the increase in calcium current and was independent of cyclic AMP. Both effects are complementary with the beta-adrenergic stimulation and can help healthy cells to compensate the failing zone from which ATP could be released.
Lymphatic pumping in response to changes in transmural pressure is modulated by erythrolysate/hemoglobin.
Authors: Elias R M , Wandolo G , Ranadive N S , Eisenhoffer J , Johnston M G
Published: June 2012

Red blood cells and lysate products (erythrolysate) are observed consistently in lymph draining acute and chronic inflammatory reactions and from tissues subjected to trauma or surgical procedures. Using hemoglobin as a marker for erythrolysate, we have measured hemoglobin in lymph up to the 10(-6) M range in a number of pathophysiological states. Data demonstrate that erythrolysate alters the pumping characteristics of lymphatic vessels. To test the effects of erythrolysate on lymphatic pumping, bovine lymphatics were suspended in an organ bath preparation with the vessels cannulated at both inflow and outflow ends. By raising the heights of the Krebs reservoir and the outflow catheters appropriately, a transmural pressure that stimulated pumping activity could be applied to the vessels. With a fixed transmural pressure of 6 cm H2O applied to the ducts, sheep erythrolysate depressed pumping activity between 40% and 100%, with dilutions containing between 10(-8) and 10(-5) M hemoglobin. Although the active principle in the red blood cells has not been characterized, evidence from precipitation purification experiments suggests that hemoglobin is an important component. Once suppressed, pumping could be restored in many but not all vessels (often to control levels) by elevating the distending pressure above 6 cm H2O. The relation between transmural pressure and fluid pumping is expressed as a bell-shaped curve, with pumping increasing up to a peak pressure (usually 8 cm H2O) and declining at pressures above this level. By comparing pressure/flow curves, we were able to ascertain that hemoglobin shifted the lymphatic function curve to the right and, on average, reduced the maximum pumping capability of the vessels. We speculate that the presence of erythrolysate/hemoglobin in lymph may modulate the ability of lymphatic vessels to drain liquid and protein from the tissue spaces.
Evidence for decreased coronary flow reserve in viable postischemic myocardium.
Authors: Vanhaecke J , Flameng W , Borgers M , Jang I K , Van de Werf F , De Geest H
Published: June 2012

To try to unravel the complexity and heterogeneity of the "no-reflow" phenomenon and its underlying mechanisms, we studied tissue perfusion in reperfused heart muscle by using tracer microspheres in an anesthetized dog model of 90-minute coronary occlusion followed by reperfusion for 2 1/2 hours, 24 hours, or 1 week. Regional myocardial blood flow was determined both in basal flow conditions and during reactive hyperemia. The effect of intracoronary adenosine administration was examined, and the ultrastructure of postischemic myocardium was analyzed. In viable reperfused tissue (as delineated by triphenyltetrazolium chloride staining), reflow in basal conditions is unimpaired. Coronary flow reserve (as approximated by peak reactive hyperemic flow) is intact at the start of reperfusion, decreases by more than half after 2 1/2 hours, and recovers completely within 1 week. This impairment of coronary reserve can be relieved by intracoronary adenosine administration. On ultrastructural examination, the capillaries are patent. On the other hand, in irreversibly damaged myocardium, both the basal reflow impairment and the decrease in coronary flow reserve are severe and permanent. Coronary flow reserve is already decreased at the start of reperfusion, and the pharmacological intervention has no beneficial effect. Ultrastructurally, extracellular and intracellular edema invariably are present, whereas the vascular endothelium is damaged and the capillaries are packed with red blood cells. We conclude that the no-reflow phenomenon (i.e., mechanical obstruction to blood flow) is limited to infarcted tissue. In viable myocardium, however, coronary flow reserve is transiently diminished, probably because of washout and subsequent insufficient availability of the chemical mediator adenosine after breakdown and slow recovery of the precursor ATP pool.
Pulmonary model to predict the effects of series ventricular interaction.
Authors: Appleyard R F , Glantz S A
Published: June 2012

To fully describe the mechanisms of diastolic interaction between the right ventricle and left ventricle, it is necessary to understand how a change in right ventricular output (Qrvo) is transmitted across the pulmonary circulation. This series ventricular interaction is manifest as the temporal response in left ventricular filling (Qlvf) to a change in Qrvo. To quantify series interaction we used a three-element, two-parameter model of the pulmonary circulation. The parameters represented the pulmonary arterial and venous resistance and pulmonary vascular compliance. Using beat-to-beat values of mean pressure and flow measured at the input and output of the pulmonary circulation during the transient response to caval or pulmonary artery occlusion, we estimated the parameters for this model in eight open-chest dogs under control conditions, after autonomic blockade, and after fully opening the pericardium. From 110 separate data episodes, the average values of the pulmonary arterial and venous resistance and pulmonary vascular compliance were 0.14 +/- 0.08 mm Hg.sec/ml and 4.81 +/- 3.17 ml/mm Hg (+/- SD). These estimates were insensitive to the simultaneous effects of autonomic reflexes and direct ventricular interaction, so they uniquely measure the bulk transport properties of the pulmonary circulation. The time constant, which measures the response of Qlvf to a change in Qrvo, averaged 0.26 +/- 0.15 second, which implies that effects of series interaction on Qlvf are manifest within one beat. The model was also able to predict the dynamic response of Qlvf to changes in Qrvo and thus can be used to measure and predict the effects of series interaction in the intact cardiopulmonary system.
Brain natriuretic peptide-like immunoreactive innervation of the cardiovascular and cerebrovascular systems in the rat.
Authors: Saper C B , Kibbe M R , Hurley K M , Spencer S , Holmes H R , Leahy K M , Needleman P
Published: June 2012

Atrial natriuretic peptide is a potent dilator of aorta and renal and cerebral arteries and inhibits sympathetic tone in the heart in several mammalian species. We examined the possibility that a molecule related to porcine brain natriuretic peptide (pBNP), which acts at the same receptor sites as atrial natriuretic peptide, might provide an alternative source of natriuretic peptide to the cardiovascular system in the rat. An antiserum against pBNP demonstrated profuse immunoreactive innervation of the heart, cerebrovascular tree, and renal arteries. pBNP-like immunoreactive fibers ran in bundles along the surface of the heart, innervating the atria most heavily and penetrating the ventricular myocardium along the coronary arteries. There was greater density of innervation of the right side of the heart compared with the left, particularly in the ventricles, suggesting a parasympathetic origin. The entire cerebrovascular tree was innervated by immunoreactive pBNP fibers, with the densest concentration of immunoreactive fibers along the surface of the internal carotid, middle cerebral, posterior communicating, and anterior cerebral arteries. The proximal renal arteries were not innervated, but as they approached the kidney, they were invested by bundles of immunoreactive pBNP fibers. These axons followed the major branches of the renal artery into the kidney parenchyma, running along the surface of the arterioles up to their entrance into the renal glomeruli. No immunoreactive innervation of the aorta or proximal brachiocephalic, subclavian, or carotid arteries was seen. A substance related to pBNP may serve as a neuromodulator regulating cardiac output as well as blood flow in certain vascular beds.
Chronic calcium channel blockade prevents the progression of myocardial contractile and electrical dysfunction in the cardiomyopathic Syrian hamster.
Authors: Capasso J M , Sonnenblick E H , Anversa P
Published: June 2012

The programmed onset of myocardial dysfunction and its progression to congestive heart failure in the cardiomyopathic Syrian hamster is hallmarked by alterations in myocellular calcium regulation. To determine whether calcium channel blockade is effective in halting the progressive depression of myocardial contractile performance in this animal model of congestive heart failure, oral verapamil therapy was instituted at 50 days of age, and treatment continued for various durations until the time of study at either 150 or 250 days of age. Left ventricular papillary muscle isometric and isotonic performance, as well as transmembrane electrical characteristics, was depressed in diseased hamsters at 150 days of age and deteriorated further by 250 days of age. These changes were evidenced by prolongation of contraction duration, a marked depression in the load-velocity relation, and a significant prolongation in the repolarization phase of the transmembrane action potential. Myocardial functional and electrical alterations associated with the progression of life in myopathic hamsters were completely halted by verapamil therapy that was continuous from 50 days after birth until death by diastolic arrest, at 150 or 250 days of age. However, premature termination of verapamil treatment before death resulted in a progressive renewal of the functional and electrical alterations for the duration of drug termination. It is concluded that the pathological changes seen during the lifetime of the cardiomyopathic hamster can be prevented by continuous calcium channel blockade and that intermediate prevention can be attained by protracted verapamil therapy. Thus, chronic verapamil therapy may be a useful adjunct in the prevention of human congestive heart failure of similar etiology.
Endothelium-derived relaxing factor released from canine femoral artery by acetylcholine cannot be identified as free nitric oxide by electron paramagnetic resonance spectroscopy.
Authors: Greenberg S S , Wilcox D E , Rubanyi G M
Published: June 2012

Recent studies using chemiluminescence and spectrophotometry have shown that cultured and native endothelial cells release nitric oxide (NO). Pharmacological and biochemical evidence argue for and against the proposal that endothelium-derived relaxing factor (EDRF) is identical with free NO. In an attempt to identify EDRF as free NO, a bioassay technique was combined with an NO trap (hemoglobin bound to agarose; Ag-Hb), and electron paramagnetic resonance (EPR) spectroscopy was used to detect the resultant nitrosylhemoglobin (NO-Hb). Canine femoral arteries with or without endothelium were perfused with physiological saline solution containing superoxide dismutase and ibuprofen and were stimulated with acetylcholine. The relaxing activity of the effluent was monitored in canine coronary artery rings without endothelium (bioassay tissue) half-maximally contracted with U46619. Acetylcholine stimulated the release of EDRF from intact femoral arteries (but not from segments without endothelium), which relaxed the bioassay tissue by 63 +/- 5%. NO (approximately 1 and approximately 10 nM) infused directly over the bioassay tissue produced 34 +/- 8% and 96 +/- 3% relaxation, respectively (ED50, approximately 2 nM). Effluents were collected under vacuum in the absence of oxygen through a column containing Ag-Hb, and the samples were assayed for NO-Hb by EPR. Samples containing NO produced the triplet EPR signal characteristic of NO-Hb, but the effluent containing EDRF did not. Infusion of NO through the donor tissue in the presence of acetylcholine gave an EPR signal similar to that observed when NO had no contact with the tissue. Nitrite anion (up to 2.7 x 10(-2) M) produced no detectable NO-Hb in analogous experiments. Thus, EDRF released from the native endothelium of canine femoral artery cannot be identified as free NO. The present findings support a concept that EDRF may be a labile precursor of NO.
Collagen phenotypes during development and regression of myocardial hypertrophy in spontaneously hypertensive rats.
Authors: Mukherjee D , Sen S
Published: June 2012

The myocardium contains collagen matrix that is a major determinant of its architecture, structural integrity, and mechanical properties. This fibrillar matrix consists primarily of type I and type III collagens having epimysial, perimysial, and endomysial components. The present study shows the alteration of collagen phenotypes during the evolution of hypertensive hypertrophy. Therapy with captopril, an angiotensin-converting enzyme inhibitor that regresses cardiac hypertrophy, not only reduces the total amount of collagen but reverses the altered distribution of type I and type III collagen. In normotensive rats, captopril did not significantly reduce collagen content or alter the ratio of type I to type III collagen.
Characterization of the vascular thromboxane A2/prostaglandin endoperoxide receptor in rabbit aorta. Regulation by dexamethasone.
Authors: Sessa W C , Halushka P V , Okwu A , Nasjletti A
Published: June 2012

Recently, we have shown that dexamethasone treatment of rabbits specifically reduces vascular smooth muscle responsiveness to agonists that interact with the vascular thromboxane A2/prostaglandin H2 (TXA2/PGH2) receptor. One potential site at which dexamethasone can influence prostanoid-mediated vasoconstriction may be at the level of the vascular TXA2/PGH2 receptor. Therefore, we characterized the vascular TXA2/PGH2 receptor in rabbit aortic membranes and examined the influence of dexamethasone treatment on vascular TXA2/PGH2 receptor affinity and number. The binding of [125I][1S-(1 alpha,2 beta(5Z),3 alpha(1E,3R)4 alpha)]-7-[3-(3- hydroxy-4-(p-iodophenoxy)-1-butenyl)-7-oxabicyclo[2.2.1] heptan-2-yl]-5-heptanoic acid ([125I]BOP), a potent TXA2/PGH2 receptor agonist, to rabbit aortic membranes was saturable, displaceable, and dependent on protein concentration. Scatchard analysis of equilibrium binding data disclosed one class of high affinity binding sites with a Kd of 0.44 +/- 0.13 nM and a Bmax of 114.4 +/- 5.2 fmol/mg protein (n = 7). Removal of the endothelium before membrane preparation did not significantly alter the affinity or number of binding sites for [125I]BOP. Kinetic analysis of the rates of [125I]BOP association/dissociation yielded a Kd of 0.62 nM. The ability of various agonists at the TXA2/PGH2 receptor to displace [125I]BOP from vascular membranes correlated well with their contractile potencies in rabbit aortic rings. Moreover, stereospecific displacement of [125I]BOP binding in aortic membranes and inhibition of U46619-mediated aortic contractions were obtained with the stereoisomers L657925(-) and L657926(+). Collectively, these data suggest that this binding site represents the functionally relevant vascular TXA2/PGH2 receptor. In functional experiments, [127I]BOP induced concentration-dependent contractions of the rabbit aorta, which were reduced by 52% in vessels from dexamethasone-treated rabbits.(ABSTRACT TRUNCATED AT 250 WORDS)
Decreased hydrodynamic resistance in the two-phase flow of blood through small vertical tubes at low flow rates.
Authors: Cokelet G R , Goldsmith H L
Published: June 2012

The aggregation of red blood cells in blood flowing through small tubes at very low shear rates leads to the two-phase flow of an inner core of rouleaux surrounded by a cell-depleted peripheral layer. The formation of this layer is known to be accompanied by a decrease in hydrodynamic resistance to flow. To quantitate this effect, we measured the pressure gradient, flow rate, and the radius of the red blood cell core in suspensions flowing through tubes of 172-microns radius at mean linear flow rates (U) from 50 to 0.15 tube diameters.sec-1. Washed red blood cells were suspended in 1.5% buffered dextran 110 at hematocrits of 34-52%. Using syringe pumps, blood flowed from a stirred reservoir through a vertical 12-cm length of tube in either the upward or downward direction. The pressure drop was measured with transducers. Mean values in distributions in the core radius were obtained by analyzing cine films of flow taken through a microscope with flow in the upward direction, measuring the core radius at five equally spaced axial positions of the tube in each of 100 frames. At 34% and 46% hematocrit, the hydrodynamic resistance increased as U decreased from 50 sec-1, reaching a maximum at U-2 sec-1. It then decreased to a minimum at U less than 0.5 sec-1 as the red blood cell core formed in the tube, and the mean core radius/tube radius ratio decreased from 0.98 to 0.74 with marked axial fluctuations at the lower U. At higher hematocrits, both the increase and decrease in hydrodynamic resistance were greater. In a red blood cell albumin-saline suspension, where there is no aggregation of red blood cells and no two-phase flow, hydrodynamic resistance increases linearly with decreasing U. The experimental results were compared with the predictions of a two-phase steady-flow model, assuming axisymmetric flow of a core surrounded by cell-free suspending medium. Two models were considered, one in which the core is solid, the other in which the rheological properties of the suspension in the core are given by the Quemada equation. The effects of sedimentation of the core resulting in a zero net flow pressure gradient were taken into account. Provided that an experimentally extrapolated value for the zero pressure gradient was used, the Quemada-fluid model gave good agreement with the experimentally observed core radius as a function of U and hematocrit.
Patterned growth of neonatal rat heart cells in culture. Morphological and electrophysiological characterization.
Authors: Rohr S , Schölly D M , Kléber A G
Published: June 2012

A culture method was developed that permits patterning of the growth of ventricular myocytes of neonatal rats. Regions were created on the culture substrate that either prevented (photoresist coat) or supported (glass surface) attachment of cells. In this way the geometry of interconnecting growth channels could be specified. Single-layered myocyte strands of variable length and with widths of as little as 65 micron (three to four cells wide) were obtained. The shape and orientation of the individual myocytes were a function of growth-channel width: the narrower the channel, the more elongated the cells and the more likely was the long axis to be oriented along the channel axis. In channels with width of 100 micron or less, cells were aligned longitudinally and cross-striated as in vivo. A high degree of morphological cell differentiation required the presence of contractile activity. Maximal diastolic potential (-71 mV), action potential amplitude (93 mV), and maximal upstroke velocity (140 V/sec) did not change with increasing culture age. Mean longitudinal conduction velocity was 0.39 m/sec. No electrophysiological or morphological evidence of photoresist toxicity was seen, and the data indicate a high degree of cell differentiation in the patterned cell cultures. The method thus is suitable for the study of the relation between impulse propagation and structure at a cellular level in artificial networks of predefined shape.
Nonadrenergic noncholinergic innervation. Anatomic distribution of calcitonin gene-related peptide-immunoreactive tissue in the dog heart.
Authors: Ursell P C , Ren C L , Albala A , Danilo P
Published: June 2012

Calcitonin gene-related peptide (CGRP) has inotropic and chronotropic effects in rat and guinea pig hearts. It also may mediate nonadrenergic noncholinergic regulation of canine cardiac electrophysiology. In this study, immunohistochemistry was used to determine the anatomic distribution of CGRP in mature dog heart and autonomic ganglia controlling cardiac function. The stellate ganglia had scattered CGRP-immunoreactive cells and nerve processes; intracardiac ganglia contained stained nerve processes but no CGRP-immunoreactive cells. Although the extramural coronary arteries were modestly innervated by varicose individual nerve processes, the great majority of CGRP-immunoreactive neural tissue in the heart existed adjacent to the sinoatrial node where varicose nerve processes coursed in numerous large nerve bundles. Each bundle contained only a few stained processes, however, indicating that CGRP-immunoreactive nerve processes were accompanying another type of autonomic tissue. Double staining and immunoultrastructure confirmed that the nerve bundles were heterogeneous. Similar nerve bundles were fewer in the left atrium, the region of the atrioventricular node, atrioventricular bundle, and the ventricles. In contrast to the distribution of sympathetic neural tissue, CGRP-immunoreactive nerve processes virtually were nonexistent among muscle fibers. We conclude that 1) CGRP-immunoreactive neural tissue likely affects sympathetic and parasympathetic ganglia that control cardiac function, 2) the preponderance of this nonadrenergic noncholinergic tissue near regions of specialized muscle (especially the sinoatrial node) suggests an efferent function in the canine heart, and 3) the presence of varicosities along CGRP-immunoreactive nerve processes within heterogeneous nerve bundles may indicate that direct axo-axonal contact is the mechanism by which these nonadrenergic noncholinergic nerve processes modulated other autonomic neural tissue.
Adenine nucleotide changes in kidney, liver, and small intestine during different forms of ischemic injury.
Authors: Zager R A
Published: June 2012

The purpose of this study was to better characterize renal adenine nucleotide pool responses to different forms of shock, contrast the changes to those found in other intra-abdominal organs (the liver and small intestine), and assess whether these changes are closely mimicked by those produced by renal arterial occlusion, the usual method used to study ischemic acute renal failure. Rats were subjected to hemorrhagic shock, septic shock, or cardiopulmonary shock of varying severities and durations. The liver consistently had the greatest energy depletion, followed by the kidney, and then the small intestine. However, only the kidney developed clear morphological damage (S3 brush border sloughing). Kidney adenylate pools were better preserved during septic shock and cardiopulmonary shock than during hemorrhagic shock despite comparable blood pressures. Only profound hemorrhagic shock (35-40 mm Hg for 25 minutes) decreased total adenylate pools (ATP + ADP + AMP). However, the degree of renal catabolite (nucleosides plus purine base) accumulation did not correlate with the amount of renal total adenine nucleotide depletion, partially because circulating catabolites contributed to intrarenal catabolite pools. Purine base/uric acid ratios differed among shocked organs, consistent with different degrees of xanthine oxidase activity (small intestine greater than liver greater than kidney). Renal morphological damage decreased during the immediate (0-30 minutes) postshock period, and the extent of this improvement was not altered by xanthine oxidase inhibition (oxypurinol), suggesting that the immediate postshock period is not one of serious oxidative injury. Shock, in comparison with renal arterial occlusion, caused only modest ATP loss/catabolite accumulation, very low purine base/uric acid ratios, and no immediate-reperfusion (0-30 minutes) resynthesis of the total adenylate pool. Thus, ischemia-induced renal adenylate changes may differ considerably, depending on the nature of the ischemic event.
L-arginine evokes both endothelium-dependent and -independent relaxations in L-arginine-depleted aortas of the rat.
Authors: Schini V B , Vanhoutte P M
Published: June 2012

This study was designed to investigate the effects of L-arginine (the substrate for the formation of endothelium-derived nitric oxide) in vascular tissues. Rat aortic rings, with or without endothelium, were suspended in organ chambers for the measurement of isometric tension; they were contracted with phenylephrine (10(-6) M). After a short incubation period (0.5 hour) in physiological salt solution, L-arginine induced minor changes in both types of rings. In contrast, when the incubation time was increased (2, 4, 6, and 8 hours), L-arginine evoked concentration- and time-dependent relaxations in aortic rings both with and without endothelium. The relaxations were larger in rings with endothelium. The presence of L-arginine (10(-3) M) in the incubation medium inhibited subsequent relaxations evoked by the amino acid. The concentration-relaxation curves associated with acetylcholine in rings with endothelium and the curves associated with Sin-1, a spontaneous donor of nitric oxide, in rings with or without endothelium were slightly but significantly shifted to the right after a 6-hour incubation. Nitro-L-arginine (3 x 10(-5) M) and methylene blue (3 x 10(-7) M) attenuated the relaxations evoked by L-arginine in rings both with and without endothelium. Other basic amino acids (D-arginine, L-homoarginine, L-citrulline, L-lysine, and L-ornithine; all tested at 10(-3) M) either had no effect or induced small relaxations and did not affect the response to L-arginine. These observations suggest that L-arginine specifically and stereoselectively relaxes aortic rings with and without endothelium, probably by restoring the endogenous pool of the amino acid, which is likely depleted by prolonged incubation.(ABSTRACT TRUNCATED AT 250 WORDS)
[Ca2+]i transients in the cardiomyopathic hamster heart.
Authors: Wikman-Coffelt J , Stefenelli T , Wu S T , Parmley W W , Jasmin G
Published: June 2012

Intracellular [Ca2+] transients were studied in isolated hearts of healthy and cardiomyopathic hamsters in late failure perfused with glucose or pyruvate. Hearts of healthy hamsters developed similar pressures when perfused with either glucose or pyruvate, and [Ca2+]i transients were comparable in amplitude when perfused with either substrate. On the other hand, hearts of cardiomyopathic hamsters in late failure developed normal pressure when perfused with pyruvate but developed depressed pressure (50%) when perfused with glucose. The amplitude of [Ca2+]i transients fell severely and was associated with a high diastolic [Ca2+]i in cardiomyopathic hamster hearts when the perfusate was switched from pyruvate to glucose. The high phosphomonoester sugars as evidenced by 31P nuclear magnetic resonance studies and the depressed oxygen consumption in the cardiomyopathic hamster hearts perfused with glucose reflect an inhibition in glycolysis and a subsequent decrease in mitochondrial activity. Without an adequate delivery of substrate to the mitochondria in the cardiomyopathic hamster, the myocardium is no longer capable of maintaining its [Ca2+]i homeostasis.
Effect of preconditioning ischemia on reperfusion arrhythmias after coronary artery occlusion and reperfusion in the rat.
Authors: Hagar J M , Hale S L , Kloner R A
Published: June 2012

Severe arrhythmias occur predictably on reperfusion after 5 minutes of coronary occlusion in the rat. There is little data available on whether ischemic preconditioning (PC) of hearts can reduce the incidence of such arrhythmias. The effect of PC (three cycles of 2 minutes of coronary occlusion and 5 minutes of reperfusion) on development of arrhythmias after a subsequent 5-minute coronary artery occlusion and reperfusion was studied. Rats (n = 16 each group) underwent 5-minute occlusion and reperfusion alone or preceded by PC; arrhythmias were monitored during ischemia and for 10 minutes of reperfusion, and biopsies were taken for creatine phosphate and adenosine triphosphate in ischemic and nonischemic zones of the left ventricle. PC reduced the incidence of ventricular tachycardia (VT) during occlusion (81% control versus 13% PC, p less than 0.001). On subsequent reperfusion, ventricular fibrillation (VF) developed in zero PC animals versus 13 (81%) of controls (p less than 0.001), and irreversible VF in zero of PC versus seven (44%) of controls (p = 0.007). VT occurred in four (25%) of PC versus all (100%) of controls (p less than 0.001). PC reduced mean duration of VT plus VF from 320 +/- 54 to 5 +/- 1 seconds (p less than 0.001) and delayed arrhythmia onset from 8 +/- 2 to 85 +/- 35 seconds after reperfusion. There was no difference in creatine phosphate levels in the ischemic zone at the end of reperfusion in PC animals compared with controls without irreversible VF (16.2 +/- 4.1 versus 15.5 +/- 3.9 nmol/mg protein, p = NS).(ABSTRACT TRUNCATED AT 250 WORDS)
Two arterial effective reflecting sites may appear as one to the heart.
Authors: Burattini R , Knowlen G G , Campbell K B
Published: June 2012

The relation between reflected waves and features of ascending aortic pressure waveforms and impedance patterns was investigated with a modified T-tube model of the systemic arterial circulation. Ascending aortic pressure and flow and descending aortic flow were measured in 10 dogs under basal conditions and under the effect of an agent (methoxamine) that caused vasoconstriction and an increase of mean aortic pressure. A broad range of aortic pressure amplitudes and features was obtained. These waveshapes were classified into four groups. Under basal conditions, cases for which a prominent diastolic fluctuation was present (n = 8) were grouped in A. Cases for which this fluctuation was absent (n = 2) were grouped in B. Groups C (n = 4) and D (n = 3) included cases that, under vasoconstricted conditions, did or did not display, respectively, a diastolic fluctuation in pressure. Arterial T-tube model parameters were estimated by simultaneously fitting the model to both ascending and descending aortic flow with aortic pressure as input. A good fit was obtained in any case considered. After parameter estimation, forward and reflected waves and impedance patterns at the entrance of head circulation (head and upper limbs) and body circulation (trunk and lower limbs) as well as their merger in the ascending aorta were determined. T-tube input impedance compared well with impedance data points obtained from the ratio of corresponding harmonics of ascending aortic pressure and flow. In some cases (group A), modulus and phase spectra displayed two distinct minima, in the range from 0 to 10 Hz. In some other circumstances, these minima were less distinct (groups B and C) and could even appear as one (group D). Whether one or two minima appeared in the ascending aortic impedance spectra at low frequency and whether a prominent diastolic fluctuation did or did not appear in aortic pressure, pressure and flow waveshapes proximal to the heart were explained by the presence of two effective reflecting sites in the systemic circulation. In group B, a diastolic fluctuation in pressure was absent despite the fact that head-end and body-end reflected waves were distinct. This happened because body-end reflected waves peaked corresponding to a minimum of the head-end reflected wave. In group D, a diastolic fluctuation in aortic pressure was absent because the body-end reflected wave moved into systole and superimposed on the head-end reflected wave. This superimposition was due to increased pulse wave velocity in the body transmission path as a result of decreased arterial distensibility.(ABSTRACT TRUNCATED AT 400 WORDS)
Effects of local reduction in pressure on distensibility and composition of cerebral arterioles.
Authors: Baumbach G L , Siems J E , Heistad D D
Published: June 2012

This study examined effects of local reductions in mean and pulse pressures on cerebral arterioles in normotensive Wistar-Kyoto rats (WKY) and stroke-prone spontaneously hypertensive rats (SHRSP). WKY and SHRSP underwent clipping of one carotid artery at 1 month of age. At 10-12 months of age, mechanics of pial arterioles were examined in vivo in anesthetized rats. Bilateral craniotomies were performed to expose pial arterioles in the sham and clipped cerebral hemispheres. Stress-strain relations were calculated from measurements of pial arteriolar pressure (servo null), diameter, and cross-sectional area of the arteriolar wall. Point counting stereology was used to quantitate individual components in the arteriolar wall. Before deactivation of smooth muscle with EDTA, mean (Pm) and pulse (Pp) pressures were significantly less (p less than 0.05) in clipped than in sham arterioles in WKY (Pm, 63 +/- 2 versus 73 +/- 2 mm Hg; Pp, 23 +/- 3 versus 30 +/- 3 mm Hg) and SHRSP (Pm, 94 +/- 4 versus 110 +/- 4 mm Hg; Pp, 27 +/- 2 versus 38 +/- 3 mm Hg). Cross-sectional area of the arteriolar wall was less (p less than 0.05) in clipped than in sham arterioles in both groups of rats (1,403 +/- 125 versus 1,683 +/- 125 microns2 in WKY; 1,436 +/- 72 versus 1,926 +/- 134 microns2 in SHRSP). There was a correlation between cross-sectional area of the vessel wall and pulse pressure (r2 = 0.66), but not mean pressure (r2 = 0.09). During maximal dilatation with EDTA, the stress-strain curve was shifted to the left in clipped arterioles of SHRSP, but not of WKY, which indicates that carotid clipping in SHRSP reduces passive distensibility of cerebral arterioles. The proportion of distensible components in the vessel wall (smooth muscle, elastin, and endothelium) was reduced in clipped arterioles in SHRSP, but not in WKY. These findings suggest that 1) vascular hypertrophy of cerebral arterioles is related more closely to pulse pressure than to mean pressure, and 2) reduction of pial arteriolar pressure completely prevents cerebral vascular hypertrophy and attenuates increases in passive distensibility of cerebral arterioles in SHRSP.
Pulmonary vascular effects of prostaglandin D2, but not its systemic vascular or airway effects, are mediated through thromboxane receptor activation.
Authors: King L S , Fukushima M , Banerjee M , Kang K H , Newman J H , Biaggioni I
Published: June 2012

Prostaglandin D2 (PGD2) can cause pulmonary vasoconstriction or vasodilation depending on animal species and age. Because the constrictor effects of PGD2 in some vascular beds may be mediated through thromboxane receptors, the purpose of this study was to determine whether the vascular or bronchial effects of PGD2 are mediated through thromboxane/endoperoxide (TX/E) receptor activation. In chronically instrumented awake sheep, PGD2 (5-25 micrograms/kg i.v.) produced a dose-dependent increase in pulmonary arterial pressure and in systemic arterial blood pressure. These changes were due to increases in resistance, because cardiac output remained unchanged. PGD2 also decreased dynamic compliance at lower doses (0.1-5 micrograms/kg i.v.) than those required to produce pulmonary vasoconstriction, confirming that PGD2 is a potent bronchoconstrictor. The airway and systemic vascular effects of PGD2 were not altered by TX/E receptor antagonism. In contrast, PGD2-induced pulmonary vasoconstriction was blocked by two TX/E receptor antagonists, SQ-29,548 and AH-23848, implying that this effect is mediated through activation of TX/E receptors. The pulmonary vasoconstrictor effects of PGD2 could not be explained by thromboxane generation, because neither cyclooxygenase inhibition with ibuprofen nor thromboxane synthase inhibition with OKY-046 had any effect on PGD2 actions. In contrast, a mild but consistent pulmonary vasodilation produced by PGD2 could be uncovered if the pulmonary vascular bed was preconstricted by hypoxia with simultaneous TX/E receptor blockade. These results indicate that TX/E receptor antagonists, although still useful pharmacological probes to determine the role of TX/E receptor activation in pathophysiological processes, should not be used to infer a role of endogenous thromboxane A2. It is possible that PGD2 participates in pulmonary processes previously ascribed uniquely to thromboxane A2.
Protein kinase C modulates basal myogenic tone in resistance arteries from the cerebral circulation.
Authors: Osol G , Laher I , Cipolla M
Published: June 2012

The objective of this study was to determine whether myogenic tone in the cerebral circulation can be modified by agents that interact with protein kinase C (PKC), a modulator of intracellular calcium sensitivity. Pial arteries (194 +/- 8 microns at 125 mm Hg) were isolated from Wistar-Kyoto rats and mounted on glass microcannulas in a specialized arteriograph. Simultaneous recordings of transmural pressure and lumen diameter were made with a video-electronic system. Myogenic tone, which developed at transmural pressures above 50 mm Hg, reduced lumen diameter by 29 +/- 3%, to 136 +/- 5 microns. Staurosporine (a PKC inhibitor) or indolactam (a PKC activator) was added cumulatively to segments of arteries obtained from each animal. Staurosporine induced progressive and eventually complete dilation, with half-maximal inhibition of myogenic tone occurring at a concentration of 1.32 +/- 0.10 nM. Conversely, indolactam augmented basal tone, reducing diameter by a maximum of 62 +/- 3%, with half-maximal effects at 0.4 +/- 1.0 microM. The effects of indolactam on arterial responses to acute increases in transmural pressure were also determined to test whether this dynamic and possibly separate mechanism could be potentiated by PKC stimulation. Although basal tone was augmented, diameter responses to increased pressure were not altered. In summary, these results implicate PKC in the regulation of basal myogenic tone and resistance artery caliber, which is a major determinant of blood flow. PKC modulation did not affect diameter responses to sudden changes in transmural pressure, however, suggesting the existence of a separate sensing/transduction mechanism that has yet to be identified.
Cellular versus myocardial basis for the contractile dysfunction of hypertrophied myocardium.
Authors: Mann D L , Urabe Y , Kent R L , Vinciguerra S , Cooper G
Published: June 2012

Contractile dysfunction has been demonstrated in many previous studies of experimental right ventricular pressure-overload hypertrophy; however, given the complex changes that occur both in the cardiac muscle cell and in the multiple components of the cardiac interstitium, it is not clear whether the contractile dysfunction observed is an intrinsic property of the cardiac muscle cell or whether it is the result of a mechanically normal cardiac muscle cell contracting within an abnormal interstitial environment. The purpose of the present study was to examine the contractile behavior of cardiac muscle cells, or cardiocytes, isolated from seven cat right ventricles that were pressure-overloaded by banding the pulmonary artery; right ventricular cardiocytes from seven sham-operated cats served as controls. Cardiocytes were obtained from these cats via standard cell isolation procedures; contractile function of the cardiocytes in response to graded viscous external loads was defined by laser diffraction. The cells were stimulated to contract at a frequency of 0.25 Hz, using 100-microA direct current pulses of alternating polarity. Hypertrophied right ventricular cardiocytes obtained from banded cats showed marked systolic contractile abnormalities in comparison with right ventricular cardiocytes from sham-operated cats. The peak velocity of sarcomere shortening for the control and hypertrophied cardiocytes in 1-cp superfusate was 3.6 +/- 0.2 and 2.1 +/- 0.1 microns/sec, respectively (p less than 0.001); the maximum extent of sarcomere shortening for the control and hypertrophied cardiocytes was 0.21 +/- 0.01 and 0.14 +/- 0.01 microns, respectively (p less than 0.001). Further, the time to peak shortening in the 1-cp superfusate was significantly longer for the hypertrophied cardiocytes (150.1 +/- 3.3 versus 160.4 +/- 3.7 msec; p less than 0.04). When the relengthening properties of the cells were examined in the 1-cp superfusate, there were significant differences between cardiocyte groups. The peak rate of sarcomere relengthening was 3.5 +/- 0.2 microns/sec in the control cardiocytes and 2.2 +/- 0.17 microns/sec in the hypertrophied cardiocytes (p less than 0.001). Similarly, the time to peak velocity of sarcomere relengthening (48.8 +/- 1.8 versus 57.9 +/- 2.9 msec) and the time to 50% maximal sarcomere relengthening (57.1 +/- 3.1 versus 67.1 +/- 3.1 msec) were both significantly prolonged for the hypertrophied cardiocytes (p less than 0.02). This study shows for the first time that the contractile defect in this model of right ventricular pressure-overload hypertrophy is intrinsic to the cardiac muscle cell itself. This finding provides a basis for further, more focused investigations designed to determine the mechanisms responsible for the contractile dysfunction observed in this form of experimental cardiac hypertrophy.