bluuebunny/crossref_metadata_2025 huggingface dataset:
Hemodynamic effects of exogenous and endogenous vasopressin at low plasma concentrations in conscious dogs.
Authors: Montani J P , Liard J F , Schoun J , Möhring J
Published: June 2012

The possibility that vasopressin plays a role in cardiovascular control arouses increasing interest. We studied in unanesthetized dogs the hemodynamic consequences of 1-hour vasopressin infusions that modified plasma concentrations over a range similar to that found in physiological situations. We also examined the cardiovascular events following the stimulation of endogenous vasopressin release by an increase in plasma osmolality. In dogs with baroreceptor reflexes intact, vasopressin infusions which increased plasma vasopressin concentration by 2-20 fmol/ml did not affect mean arterial pressure. However, they significantly decreased cardiac ouput (measured by an electromagnetic flowmeter) and increased total peripheral resistance. After baroreceptor denervation, vasopressin infusion rates as low as 40 fmol/kg per min (0.017 microU/kg per min) led to an increase in mean arterial pressure. Cardiac output was unaffected until much higher infusion rates were used. Changes in total peripheral resistance were very similar to those calculated in dogs with intact baroreceptors. The release of vasopressin following infusions of hypertonic solutions either intravenously or into a carotid artery induced detectable hemodynamic changes which appeared in many respects similar to those following low infusion rates of vasopressin. We conclude that physiological plasma concentrations of vasopressin have hemodynamic effects even though they do not normally modify arterial pressure, presumably because of some particular interaction of vasopressin with the baroreceptor reflex.
Acute renovascular hypertension in conscious dogs. Interaction of the renin-angiotensin system and sympathetic nervous system in systemic hemodynamics and regional blood flow responses.
Authors: Gavras H , Liang C
Published: June 2012

The effects of acute renovascular hypertension on the sympathetic nervous system, regional blood flow and cardiac function were studied in conscious dogs submitted to renal artery occlusion by inflation of a cuff implanted previously around one renal artery. We then compared the alterations in plasma renin and catecholamine levels and in the various hemodynamic parameters induced by those maneuvers in intact dogs, to those in dogs pretreated with alpha- and beta-adrenergic receptor blockers. Subsequently, the converting enzyme inhibitor teprotide was administered to inhibit angiotensin formation in both experiments. Our results suggest that both the renin-angiotensin system and the sympathetic system contribute to the rise in blood pressure. The hemodynamic changes and alterations in regional blood flows accompanying this acute hypertension appear to be due mostly to the increase in plasma angiotensin, since prior adrenoceptor blockade only attenuated their magnitude but did not alter their direction. However, angiotensin-induced coronary vasoconstriction was observed only in adrenergically blocked but not intact animals, probably because of the protective effect of baroreceptor-mediated reflex sympathetic coronary vasodilation.
The contractile state of cat and dog heart in relation to the interval between beats.
Authors: Pidgeon J , Lab M , Seed A , Elzinga G , Papadoyannis D , Noble M I
Published: June 2012

We induced atrioventricular dissociation and initiated ventricular pacing in intact dogs and isolated cat hearts. Left ventricular pressure, its time derivative (dP/t), and action potentials were recorded. When a test pulse was introduced at varying intervals after a period of steady pacing, an optimum contractile response was obtained at an average interval of 720 msec. A similar optimum interval was obtained after pacing at various frequencies and after paired pulse stimulation but was shortened to 560 msec after infusion of epinephrine. The magnitude of the optimum contractile response increased with an increase in the frequency of prior pacing which was accompanied by an increase in the time the cell membrane was depolarized. The optimum contractile response following paired pulse stimulation was greater than that following regular pacing, with the same number of stimuli per minute and the same time of membrane depolarization. The results are explicable in terms of intracellular calcium ion recirculation with separate compartments for release to and uptake from the contractile proteins. A negative feedback control of Ca2+ inflow to the cell by intracellular Ca2+ content is postulated to explain the effect of paired pulse stimulation and shortening of action potential duration following an increase in regular pacing frequency.
Caffeine reversal of length-dependent changes in myocardial contractile state in the cat.
Authors: Chuck L H , Parmley W W
Published: June 2012

The present study evaluated potential mechanisms for the slow length-dependent change in myocardial contractile state. Using 40 isolated right ventricular cat papillary muscles, we found that 10 mM caffeine reversed the subsequent slow change in myocardial performance following a change in muscle length. Since caffeine acts both at the sarcolemma and the sarcoplasmic reticulum, we attenuated the sarcolemmal influx of calcium with verapamil, manganese, and low external calcium concentration. None of these interventions altered the caffeine reversal of the length-dependent effect. It thus appears that the length-dependent alteration of contractile state is of intracellular origin, and probably related to altered calcium handling by the sarcoplasmic reticulum.
Ultrastructure of human umbilical arteries. Studies on arteries from newborn children delivered by nonsmoking, white group D, diabetic mothers.
Authors: Asmussen I
Published: June 2012

The effect of diabetic metabolism on the human vascular wall studied, using the fetal cardiovascular system at birth as an experimental model. The ultrastructure of umbilical arteries from nine newborn children of nonsmoking diabetic mothers (White group D) was compared with that of 30 healthy nonsmokers. Intimal cushions, thickening of the basement membrane often with a multilaminal appearance, and glycogen accumulations, both in the cells of the intima and the media, were found. The cells of the intima were very rich in fibrillas, identical to the underlying media myocytes. Endothelial cell death with formation of a pseudoendothelium due to migrating myocytes might be the explanation.
Significance of sodium, sympathetic innervation, and central adrenergic structures on renal vascular responsiveness in DOCA-treated rats.
Authors: Berecek K H , Murray R D , Gross F
Published: June 2012

The effects of sodium, sympathetic innervation, and central adrenergic structures on the development of changes in renal vascular reactivity were studied in unilaterally nephrectomized rats treated with a single implant of deoxycorticosterone acetate (DOCA; 100 mg/kg). Vascular reactivity to norepinephrine (NE) and vasopressin (ADH) was assessed in isolated kidneys perfused with a synthetic medium. Influence of sodium was determined by placing DOCA-treated rats on high, normal, and low sodium intakes. Neural influence was studied by means of local denervation of the renal artery and by intravenous (iv) and intraventricular (ivt) administration of 6-hydroxydopamine (6-OHDA). Marked changes in renal vascular reactivity in DOCA-treated rats were already apparent prior to the rise in blood pressure. Dose-response curves for NE and ADH showed parallel leftward shifts and decreased threshold doses. Normal sodium intake, local denervation, and peripheral sympathectomy had no effect on the development of these vascular changes in DOCA-treated rats. However, sodium deficiency and ivt administration of 6-OHDA totally prevented development of enhanced vascular reactivity. These results imply that increased vascular reactivity is a major factor in the development of DOCA-hypertension.
Trophic effect of norepinephrine on the rat portal vein in organ culture.
Authors: Abel P W , Trapani A , Aprigliano O , Hermsmeyer K
Published: June 2012

Rat portal veins were maintained in organ culture to study the development of characteristic denervation changes and a possible trophic effect of the neurotransmitter norepinephrine (NE). Vessels maintained in organ culture for 2 days showed supersensitivity to NE and Ba2+, a more rapid rate of relaxation from a Ba2+ contracture, and partial depolarization of the myovascular cells. All of these changes except the quicker relaxation from Ba2+ contracture could be prevented by incubating the preparations in a NE-containing medium. This evidence suggests that functional changes in vascular muscle cells are caused by the removal of a tropic influence of NE, but can be prevented by NE replacement. However, the failure of NE in the culture media to prevent the increased rate of relaxation from Ba2+ contracture found after 2 days in organ culture suggests that NE is not the only trophic influence acting on the portal vein. In addition, incubation of veins in a NE-containing medium produced a marked subsensitivity to the contractile effects of NE, but not BA2+, and thus possible desensitization of noradrenergic receptors. The data thus support a trophic role for NE in the rat portal vein.
Mechanism(s) of altered mitochondrial calcium transport in acutely ischemic canine hearts.
Authors: Sordahl L A , Stewart M L
Published: June 2012

Studies were undertaken to determine the mechanisms leading to altered mitochondrial function in ischemic myocardium. A new procedure has been developed to routinely isolate 60-70% of the total mitochondrial protein from heart tissue. After 1 hour of ischemia, mitochondria exhibit decreases of more than 50% in phosphorylating respiration for both NADH- and succinate-linked substrates compared to controls. However, no significant decreases in the efficiency of mitochondrial ATP synthesis (ADP:0) or ATPase activity are observed. Rates of substrate-driven Ca2+ uptake exhibit decreases greater than that seen with phosphorylating respiration with incomplete uptake and premature release of Ca2+. Spectrophotometric measurements in ischemic heart reveal rapid oxidation or loss of mitochondrial NADH with marked "swelling" of the inner membrane compartment; both changes parallel the loss of Ca2+. Significant losses in intramitochondrial adenine nucleotides also are found. Mitochondrial retention of accumulated Ca2+ can be restored by addition of small amounts of exogenous adenine nucleotides (ATP or ADP) with concomitant attenuation of both NADH oxidation and "swelling." The data indicate that, following 1 hour of ischemia, the efficiency of mitochondrial ATP production is still relatively intact whereas both electron transport chain activity and calcium transport are severely compromised. These decreases appear to be related to selective membrane damage in the mitochondrial inner membrane.
Baroreceptor function in spontaneously hypertensive rats. Effect of preventing hypertension.
Authors: Andresen M C , Brown A M
Published: June 2012

In the previous paper we showed that baroreceptor resetting in spontaneously hypertensive rats (SHR) resulted from an incomplete matching of increased receptor strain sensitivity with reduced vessel wall distensibility. Here SHR and Wister-Kyoto controls were treated with antihypertensive drugs in their drinking water (reserpine, hydrochlorothiazide, and hydralazine) from 5 weeks of age so that we might examine the role of blood pressure in the SHR vessel wall-receptor mismatch. Radius and receptor properties were measured using the in vitro aortic arch-aortic nerve preparation at 8, 14, 20, and 30 weeks. We found that baroreceptors from SHR with normal blood pressures had normal pressure thresholds and suprathreshold pressure sensitivities. However, the treated SHR receptors still had lower strain thresholds and the aortas still were less distensible than were the normal. Now, however, the increased receptor sensitivity was sufficient to normalize the relationship between baroreceptor function and arterial blood pressure. We conclude that, although blood pressure may be restored to normotensive levels by therapy, vascular abnormalities may continue to develop.
The role of the renin-angiotensin system in mediation of adrenal catecholamine secretion in the cat induced by intrarenal beta-adrenergic stimulation.
Authors: Krausz M M , Feuerstein G , Feuerstein N , Gutman Y
Published: June 2012

Isoproterenol infusion (0.1 microgram/kg per min) into the renal artery of the cat induced an increase in plasma renin concentration (PRC) from 14.3 +/- 5.7 (mean +/- SE) ng angiotensin I/ml per hr to 56.8 +/- 7.7 after 70 minutes (P < 0.05) and an increase in catecholamine secretion rate from 38.7 +/- 6.0 ng/kg per 10 min to 180.0 +/- 40.0 after 70 minutes (P < 0.001). Intravenous infusion of the same dose of isoproterenol had no significant effect on adrenomedullary catecholamine secretion rate. Isoproterenol induced preferential norepinephrine release: the ratio of norepinephrine to epinephrine secretion changed from 11.5:23.7 during the control period to 130.0:40.1 70 minutes after the start of isoproterenol administration. Intrarenal infusion of propranolol (3.0 mg/kg per min) inhibited renal renin release and adrenal catecholamine secretion in response to intrarenal isoproterenol. Intravenous infusion (0.4 microgram/kg per min) of an angiotensin II antagonist [Sar1, Ileu8]angiotensin II abolished the catecholamine response to intrarenal isoproterenol infusion. It is suggested that intrarenal isoproterenol infusion stimulates renal renin release and angiotensin production which, in turn, stimulates a preferential secretion of adrenomedullary norepinephrine.
Role of medullary hemodynamics in the natriuresis of drug-induced renal vasodilation in the rat.
Authors: Lameire N , Vanholder R , Ringoir S , Leusen I
Published: June 2012

In contrast to most renal vasodilators, such as acetylcholine (ACh), secretin increases renal blood flow in the dog without a marked effect on sodium excretion (UNaV). To investigate this observation, we studied the relationship between renal vasodilation, UNaV, and papillary plasma flow (PPF) in rats, infused either with ACh or secretin into the aorta at the level of both renal arteries. ACh significantly increased GFR, PAH clearance, and UNaV (delta + 0.35 ml/min, + 2.11 ml/min and + 1.77 muEq/min, respectively; P < 0.05). PPF rose from 50 +/- 2.6 ml/min 100 g (mean +/- SE) in control rats to 91 +/- 4.7 ml/min 100 g after ACh (p < 0.001). Despite a similar increase in PAH clearance after secretin (+ 2.21 ml/min; P < 0.01), UNaV remained unchanged and PPF was only slightly, although significantly, increased (from 50 +/- 2.6 ml/min 100 g to 65 +/- 2.75 ml/min 100 g; P < 0.05). Both total kidney and papillary vasodilation, and the increase in UNaV after ACh were blocked by previous administration of meclofenamate (M), a prostaglandin inhibitor. No effect of M in secretin-infused rats was observed. In conclusion, the relationship between a total renal vasodilation and natriuresis was dissociated with secretin, but not with ACh. However, a relationship between the natriuresis and influence on papillary hemodynamics was observed with both vasodilators. Finally, the renal hemodynamic and natriuretic effects of ACh are probably mediated by prostaglandin release.
The effect of verapamil on mechanical performance of acutely ischemic and reperfused myocardium in the conscious dog.
Authors: Sherman L G , Liang C , Boden W E , Hood W B
Published: June 2012

The effect of verapamil, an inhibitor of transmembrane calcium flux, was studied in intact conscious dogs with myocardial ischemia produced by inflating a balloon cuff implanted on the left anterior descending coronary artery. Six dogs received a continuous infusion of verapamil (10 microgram/kg per min) beginning prior to coronary occlusion, and six received normal saline infusions. Systolic ejection shortening (SES) was measured from subendocardial ultrasonic crystals implanted in the central ischemic zone (IZ) and border zone (BZ), and in a nonischemic control zone (CZ). Hearts were paced at a constant heart rate with periodic introduction of closely coupled extrasystoles. SES was measured both for normally paced beats and during postextrasystolic potentiation (PESP). Regional myocardial blood flow was measured by injecting radioactive microspheres before, during, and after coronary occlusion. There were no significant differences between verapamil-treated dogs and saline control dogs in mean aortic pressure, heart rate, left ventricular end-diastolic pressure or dP/dt, cardiac output, or regional myocardial blood flow in IZ, BZ, or CZ. Differences in mechanical performance between two groups were noted, however. In the IZ, SES was abolished completely for normally paced beats in both groups but was significantly preserved for PESP beats in the verapamil-treated animals. In the BZ, SES was significantly reduced for normally paced beats only in the saline controls, and PESP responses were preserved to a significantly greater degree in the verapamil-treated animals. These results indicate that verapamil pretreatment exerts beneficial effects upon mechanical performance of ischemic myocardium. Since no changes in systemic hemodynamics or regional myocardial blood flow were observed, the effect may be due to the calcium-antagonistic properties of the agent.
Pacing-induced automaticity in sheep Purkinje fibers.
Authors: Wald R W , Waxman M B
Published: June 2012

The induction and decay of pacing-induced automaticity were studied in 15 sheep Purkinje fiber preparations superfused with modified Tyrode's solution containing norepinephrine, 2.5 x 10(-7) M. All preparations were quiescent prior to pacing. Spontaneous automaticity could be induced in each preparation provided a sufficient number of pacing stimuli were applied at a fast enough rate. Once the minimum pacing requirements for induction of automaticity were exceeded, the number, total duration, and fastest rate of the induced beats were proportional to the number and rate of the pacing stimuli up to a maximum which could not be exceeded. Consecutive trains of stimuli were additive in inducing automaticity, provided that the pauses between them were short enough to preclude the time-dependent return of automatic properties to their pre-pacing level. Prolonged sequence of fixed pacing trains resulted in stable degrees of automaticity which depended on the length of the pause between them. These observations permit a semiquantitative description of induced automatic behavior and help establish a model that may be useful in future studies.
The cardiocardiac sympathetic reflex during coronary occlusion in anesthetized dogs.
Authors: Felder R B , Thames M D
Published: June 2012

Cardiac sympathetic afferent fibers activated during coronary occlusion exert an excitatory influence on sympathetic discharge to the heart in cats after spinal cord section. The significance of this cardiocardiac sympathetic reflex response during myocardial ischemia in animals with an intact neuraxis is unknown. We studied the responses of efferent cardiac sympathetic nerve activity (CSNA), arterial pressure, and heart rate to coronary occlusion in two groups of dogs with cardiac sympathetic reflexes intact and with other reflex inputs affecting CSNA sectioned or controlled. In group I (n = 10), the vagi were sectioned, the spinal cord remained intact, and the carotid sinuses were isolated and perfused to maintain baroreceptor input constant. Coronary occlusion was performed at moderate and low basal levels of CSNA by setting carotid sinus pressure at 125-150 and 200 mm Hg, respectively. Under these conditions, CSNA was not altered by occlusion of either the anterior descending or the circumflex coronary artery. In group II (n = 4), the vagi were sectioned and the spinal cord was interrupted. In these dogs, CSNA increased significantly (61 +/- 19%) during coronary occlusion. These results show that an excitatory cardiocardiac sympathetic reflex can be demonstrated in dogs with spinal cords sectioned but not with spinal cords intact. This finding is consistent with the view that inhibitory bulbospinal pathways minimize the influence of the spinal cardiocardiac sympathetic reflex during myocardial ischemia in anesthetized dogs.
Relationship between structure and fatty acid metabolism in mitochondria isolated from ischemic rat hearts.
Authors: Feuvray D , Plouët J
Published: June 2012

We studied mitochondrial structure and intermediates of fatty acid metabolism in mitochondria isolated from ischemic hearts. By electron microscopy, no structural difference was detected between mitochondria isolated from control hearts and from ischemic hearts receiving glucose as the only substrate. However, major differences were observed in mitochondria obtained from control and ischemic hearts receiving both glucose and palmitate. These hearts contained a higher portion of damaged mitochondria. However, measurements of marker enzyme activities failed to show that more mitochondria were lost during the isolation procedure in ischemic than in control hearts. Many densely staining areas (or amorphous densities) were observed in the isolated mitochondria of ischemic hearts. These amorphous densities have an appearance similar to that observed in the intact ischemic heart under the same perfusion conditions. Levels of long-chain acyl-CoA in mitochondria isolated from hearts receiving glucose alone were practically the same for control and ischemic hearts and were only slightly increased in mitochondria of ischemic hearts receiving both glucose and palmitate. On the other hand, levels of long-chain acyl carnitine in mitochondria of ischemic hearts were twice those found in control hearts. The mitochondrial level of long-chain acyl carnitine was approximately four times higher in the ischemic hearts receiving palmitate compared to those receiving no palmitate. This rise in long-chain acyl carnitine levels in mitochondria isolated fom ischemic hearts receiving palmitate may be related to modifications of the mitochondrial structure and to the appearance of amorphous densities.
The effect of hypophysectomy on experimental endothelial cell regrowth and intimal thickening in the rat.
Authors: Bettmann M A , Stemerman M B , Ransil B J
Published: June 2012

We studied the influence of hypophysectomy on endothelial cell regrowth and intimal thickening following aortic endothelial removal. Modification of this influence by replacement doses of glucocorticoids, mineralocorticoids, thyroxin, and growth hormone also was investigated. Young adult male rats were used, and endothelial removal was achieved by the balloon catheter method. Percent endothelial regrowth and percent intimal thickening were quantified 1 or 2 weeks after injury (3 or 5 weeks after hypophysectomy). One week after injury, endothelial regrowth was 64% in hypophysectomized rats and only 54% in controls. At 2 weeks, values were 80% and 79% respectively. Intimal thickening (percent of wall thickness due to intima) at 1 week was 11% in hypophysectomized and 14% in control rats. At 2 weeks, values were 13% and 22%, respectively. All differences between hypophysectomized and control rats at 2 weeks were statistically significant. Neither endothelial regrowth nor intimal thickening in hypophysectomized rats was altered by hormone replacement. Comparison of areas in which endothelium had not regrown suggested that hypophysectomy had a direct effect on intimal smooth muscle cell proliferation. Thus, hypophysectomy suppresses intimal thickening and accelerates endothelial regrowth after wall injury. Neither effect depends on certain known hormones, and these effects are to some extent independent of one another. These findings are relevant to recent work on growth factors and atherogenesis.
Microvascular pressure distribution and responses of pulmonary allografts and cheek pouch arterioles in the hamster to oxygen.
Authors: Davis M J , Joyner W L , Gilmore J P
Published: June 2012

Despite extensive investigations of the pulmonary circulation using both in vitro and in vitro preparations, few direct microcirculatory studies have been made. Consequently, the mechanisms involved in the response of the pulmonary microvasculature to changes in oxygen tension remain unclear. The present study represents the first direct observation of the responses in pulmonary microvessels to alterations in oxygen tension. Neonatal lung tissue was transplanted into the hamster cheek pouch using a chamber technique. Both tissues were characterized with respect to their microvascular pressure profile and vascular response to hypoxia. The results showed the two tissues to be remarkably different. Small pulmonary and cheek pouch arterioles exhibited opposite responses to changes in oxygen environment; hypoxia elicited a constriction of pulmonary arterioles, but a dilation of cheek pouch arterioles. Pulmonary capillary pressure, although comparable to that measured in the intact lung (13 mm Hg), was substantially lower than cheek pouch capillary pressure, which was within the range of that described for several systemic vascular beds. The microcirculatory effects of oxygen on both tissues were confined to the arteriolar segments. The characteristics of this pulmonary microcirculation are such that it is a unique model for further physiological and pharmacological studies.
Indomethacin decreases arterial blood pressure and plasma renin activity in rats with aortic ligation.
Authors: Jackson E K , Oates J A , Branch R A
Published: June 2012

Severe renovascular hypertension was produced in rats by complete aortic ligation between the origin of the renal arteries. Six days after coarctation, a carotid cannula was implanted and mean arterial blood pressure (MABP) and plasma renin activity (PRA) were determined. Subsequently, indomethacin (5 mg/kg in oil) or vehicle was administered subcutaneously three times in the following 24-hour period. On day 7, MABP and PRA were again determined. Indomethacin reduced MABP from 179.0 +/- 6.7 to 156.5 +/- 8.8 mm Hg (P less than 0.002, n = 11) and PRA from 21.2 +/- 7.3 to 9.3 +/- 2.9 ng AI/ml per hr (P less than 0.045, n = 10), whereas vehicle treatment did not alter either MABP or PRA (n = 6). There was a significant association between the decrease in MABP and the percentage decrease in PRA following indomethacin treatment (r = 0.766, P less than 0.016). A similar study was performed in aortic ligated rats in which the left kidney was removed at the time of ligation. In these animals, 6 days after surgery, MABP and PRA were 128.0 +/- 5.9 mm Hg and 0.11 +/- 0.06 ng AI/ml per hr (n = 6), respectively, and indomethacin had no effect on either MABP or PRA. These data provide evidence that the prostaglandin system is involved in the release of renin and in the pathogenesis of elevated blood pressure in this model of renin-dependent hypertension.
Myocardial function of the interventricular septum. Effects of right and left ventricular pressure loading before and after pericardiotomy in dogs.
Authors: Molaug M , Stokland O , Ilebekk A , Lekven J , Kiil F
Published: June 2012

We examined the function of the interventricular septum in six open-chest dogs by inserting piezoelectric crystals into the interventricular septum. Continuous ultrasonic recordings showed that the changes in myocardial chord length (MCL) in the septum and free walls of the right and left ventricle were similar during saline infusion and during pericardiotomy. End-diastolic MCL and myocardial shortening during ejection (MS) rose in the septum and free walls of both ventricles during saline infusion as end-diastolic MCL and MS in the septum and free walls of the ventricles, and reduced end-diastolic pressures by 1-2 mm Hg. The responses to aortic and pulmonary artery constrictions were similar before and after pericardiotomy. When aortic constriction had raised free left ventricular systolic pressure by about 60 mm Hg, end-diastolic MCL increased in the septum and free left ventricular wall, whereas end-diastolic MCL and MS of the free right ventricular wall fell. Pulmonary artery constriction increased end-diastolic MCL in the free right ventricular wall and reduced end-diastolic MCL and MS in the septum and free left ventricular wall. Thus, the myocardium, including the interventricular septum, is uniformly expanded during saline infusion and pericardiotomy. The interventricular septum behaves as part of the left ventricle during aortic and pulmonary artery constriction. The pericardium imposes a restraint on the interventricular septum and free walls of the ventricles during volume loading, but not during pressure loadings, because dilation of one ventricle is associated with shrinkage of the other.
A force-length-time relationship describes the mechanics of canine left ventricular wall segments during auxotonic contractions.
Authors: Piene H , Covell J W
Published: June 2012

We examined regional mechanics of the left ventricular free wall in naturally pumping dog hearts during beta-blockade. Local systolic wall force (F) and segment length (L) were obtained with an auxotonic force gauge and an ultrasonic dimension gauge, both inserted at the equatorial level of the wall to measure F and L in the circumferential direction. Shortening velocity (-dL/dt) was obtained by differentiation of L. Preload and afterload were changed by acute caval and/or aortic occlusion so that a wide variation in F, L, -dL/dt, and dF/dt during shortening was obtained. In all experiments, F vs. L at identical time (t) after end-diastole (ED) fell on well-defined lines, irrespective of the -dL/dt line (t = 200 msec) was equivalent to a drop of approximately 50% in F at 10% reduction in L. No defined relationship was observed between F, L, and -dL/dt. However, by superimposing F, L, and -dL/dt curves from contractions of high EDL and high -dL/dt on those from contractions of low EDL and low -dL/dt, and comparing F and -dL/dt at identical L and t, a slightly lower F (difference 2.23 +/- 1.09 g, P approximately 0.05) could be associated with the higher -dL/dt (difference 0.6 +/- 0.1 muscle length/sec, P less than 0.001). These data suggest that the F-L-t relationship is a valid descriptor of auxotonic contractions in the ventricular wall, and that the direct effect of shortening velocity on the wall force is modest.
Functional and structural changes in the rabbit ear artery after sympathetic denervation.
Authors: Bevan R D , Tsuru H
Published: June 2012

We studied the tissue weight, dimensions, contractility, elasticity, and sensitivity to exogenous norepinephrine (NE) of denervated and innervated segments of the central ear arteries of white New Zealand rabbits. Three different age groups received unilateral superior cervical ganglionectomies, "growing" at 3-4 weeks, "young adult" at 9-11 weeks, and "mature" at 16-20 weeks. In the growing group, 8 weeks after ganglionectomy, the denervated arteries showed mean decreases in tissue weight (11%), total wall thickness (12+), cross-sectional area of media (17%), contractility (16%), and increases in the tangential modulus of elasticity and sensitivity to NE (2.3-fold) compared to the contralateral control vessels. The change in medial cross-sectional area was significant in the growing and young adult but not the mature animals. The other changes, however, although consistently seen, differed quantitatively among the groups. These results indicate that an intact innervation is necessary for normal development and maintenance of the artery wall. However, the precise consequences of this influence vary at different ages. Whether this influence involves a special trophic factor is not known.
Chronic localized hypotension and resetting of carotid sinus baroreceptors. Electrophysiological and histological studies in the dog.
Authors: Igler F O , Donegan J H , Hoo K C , Korns M E , Kampine J P
Published: June 2012

Resetting of carotid sinus (CS) baroreceptors to chronically elevated systemic pressure in hypertension has been demonstrated. The effects of chronic system hypotension on CS baroreceptor afferents has not been elucidated, however. The purpose of the present study was to determine the electrophysiological and histological characteristics of CS baroreceptors exposed to chronic hypotension. Chronic unilateral hypotension was produced by anastomosis of the common carotid artery to the external jugular vein. CS nerve activity and histology of the normotensive sinus (mean CS pressure +/- SD = 96 +/- 10.9 torr) were compared to those of the hypotensive sinus (mean CF pressure 50 +/- 14.2 torr) 44-49 days after anastomosis in nine mongrel dogs. An isolated CS pouch preparation was used to produce standard pressure changes. Threshold pressure for hypotensive sinuses (15.5 +/- 5.19 torr) was significantly less (P less than 0.05) than for normotensive sinuses (40.6 +/- 9.73 torr). Saturation pressure was also significantly less in the hypotensive sinus (P less than 0.05). There were no significant differences between slopes of the stimulus-response curve or in architecture of intima or media of the two sides. Thus, the stimulus-response curve was shifted to the left in chronic CS hypotension, and this effect could not be related to a change in CS light microscopic histology.
Effect of atrial systole on canine and porcine coronary blood flow.
Authors: Bellamy R F
Published: June 2012

A feature of phasic coronary flow patterns recorded in conscious chronically instrumented dogs is the atrial cove--a transient depression of arterial flow that occurs during atrial systole. The association between the hemodynamic effects of atrial systole and the atrial cove was studied in anesthetized dogs and pigs with complete heart block. Many atrial coves are available for study in these preparations because atrial activity continues unabated during the diastolic ventricular arrest that follows cessation of electrical pacing. The effect of atrial systole is to translate the pressure-flow relation found during diastole to a higher intercept pressure without change in slope. The increase in the intercept pressure equals the increase in intramyocardial pressure measured with microtransducers embedded in the left ventricular wall. The decrement in flow during the atrial cove is a direct function of the change in intramyocardial pressure and an inverse function of coronary vascular resistance. Each atrial systole is associated with a forward flow transient in the coronary veins, the peak of which occurs at the same instant as does the nadir of atrial flow. These data suggest that the coronary vessels are acting as collapsible tubes and that the waterfall model of the coronary circulation is applicable. The following sequence is proposed to account for the atrial cove. Atrial systole ejects a bolus of blood into the left ventricle increasing both ventricular cavity and intramyocardial pressures. The increase in intramyocardial pressure raises the back pressure opposing coronary flow, reducing the arterial perfusion pressure gradient and causing flow to fall.
The deformational characteristics of the left ventricle in the conscious dog.
Authors: Olsen C O , Rankin J S , Arentzen C E , Ring W S , McHale P A , Anderson R W
Published: June 2012

We studied left ventricular minor and major axis diameters and equatorial wall thickness in eleven conscious dogs with chronically implanted pulse-transit ultrasonic dimension transducers. Left ventricular transmural pressure was measured with micromanometers. Left ventricular volume was varied by inflation of implanted vena caval or aortic occluders. The geometry of the left ventricle was represented as a three-dimensioal ellipsoidal shell. Left ventricular eccentricity was found to be a linear function of ventricular volume during both diastole and ejection. However, the relationship was not the same for diastole and ejection, and during diastole the left ventricle was mre spherical at large volumes and more elliptical at small volumes than during ejection. The rearrangements in geometry observed during isovolumic contraction appeared to be transitional stages from the diastolic to the ejection-phase relationship. Thus, during isovolumic contraction, the left ventricle became more elliptical at large volumes and more spherical at small volumes. These relationships were not altered significantly by increased afterload or inotropic interventions. We also observed that the diastolic deformation of the ventricular chamber occurred in a set and predictable manner that seemed to be determined by the three-dimensional mechanical properties of the myocardium. The geometric inter-relationships of the ventricular wall determined the relationship between diastolic transmural pressure and mural stress. These findings probably reflect basic structural characteristics of the myocardium and provide a convenient method for quantitatively representing the dynamic geometry of the left ventricle.
Electrophysiological effects of hypertonic sucrose solutions on canine cardiac Purkinje fibers.
Authors: Bailey J C
Published: June 2012

Microelectrode techniques were used to study the electrophysiological effects of hypertonic solutions on canine cardiac Purkinje fibers. Tyrode's solution was rendered hyperosmotic by the addition of sucrose to produce 320, 350, 400, and 500 mOsm solutions. Hyperosmotic solutions produced sucrose concentration-dependent hyperpolarization, increased the current required to effect all-or-none depolarization, slowed transmission, and prolonged action potential duration. The action potential prolongation was reversed or prevented by lidocaine (10-5 M). Treatment of potassium-depolarized Purkinje fibers with hypertonic solutions produced hyperpolarization, increased Vmax phase 0, decreased the current required to evoke all-or-none depolarization, increased action potential duration, and increased transmission speed. The potent electrophysiological actions of hypertonic sucrose solutions probably derive from their osmotic effects rather than from selective actions at specific membrane sites or hormone receptors.
Effects of graded increases in pulmonary vascular pressures on lung fluid balance in unanesthetized sheep.
Authors: Parker R E , Roselli R J , Harris T R , Brigham K L
Published: June 2012

Fourteen experiments were conducted on 12 chronically instrumented unanesthetized sheep in which we monitored pulmonary arterial, left atrial, and aortic pressures, lung lymph flow, and lymph-to-plasma ratios (L/P) of total proteins and four endogenous protein fractions during baseline and progressive elevations of left atrial pressure. We found that L/P for total proteins decreased as lung lymph flow increased until lymph flow exceeded four to five times baseline and thereafter remained nearly constant (filtration independent) at 0.26. The four protein fractions exhibited a filtration independent L/P that was related to the effective molecular radius of the protein fraction. The minimal L/P were 0.36, 0.28, 0.18, and 0.09 for the protein fractions that had effective molecular radii of 36, 38.5, 59, and 101 A, respectively. In addition, we found no evidence supporting a stretched pore phenomenon over the pressure range utilized in this investigation.
Loss of the glomerular contractile response to angiotensin in rats following myohemoglobinuric acute renal failure.
Authors: Wilkes B M , Caldicott W J , Schulman G , Hollenberg N K
Published: June 2012

To examine the state of the glomerulus in rats protected from acute renal failure (ARF) by prior insult, we measured the contractile responses of isolated glomeruli to angiotensin II (AII) and dibutyryl cyclic AMP (DBcAMP). In healthy rats, both agents induced a dose-related fall in glomerular diameter (P less than 0.001). Saralasin, the angiotensin antagonist, blocked the glomerular response to AII totally and to DBcAMP partially. Two weeks following ARF induced with 50% glycerol (10 ml/kg, im), azotemia had reversed and the nephrotoxic effect of mercuric chloride (4.7 mg/kg, sc) was blunted, as anticipated. AII did not reduce glomerular size, but the response to DBcAMP was sustained at this time. To determine the specificity of the loss of the glomerular response to AII, we also assessed the effects of an AII infusion (1 microgram/kg/min) on blood pressure and renal blood flow. There was a substantial rise in blood pressure (control, 104 +/- 11.8 mm Hg; AI, 131.0 +/- 5.3 mm HG; P less than 0.001) and fall in renal blood flow (control, 2.45 ml/g per min; AII, 0.81 +/- 0.10 ml/g per min; P less than 0.025). Vascular responsiveness to AII was preserved at a time when glomeruli were totally unresponsive and rats were resistant to ARF. The loss of glomerular contractility may, in part, account for the protection from ARF seen in this model: if so, glomerular abnormalities may play a pathogenetic role.
Response of isolated monkey coronary arteries to catecholamines and to transmural electrical stimulation.
Authors: Toda N
Published: June 2012

In helically cut stripes of monkey coronary arteries of different sizes, contracted with prostaglandin F2 alpha or K+, responses to norepinephrine, epinephrine, isoproterenol, and transmural electrical stimulation were compared. In response to norepinephrine, only contractions were induced in large arteries, contractions at low concentrations and relaxations at high concentrations in medium-size arteries, and only relaxations in small arteries. Epinephrine produced a greater contraction than norepinephrine in the arteries. Relaxant effects of isoproterenol were greater in small and medium-size arteries than in large arteries. Transmural electrical stimulation applied at frequencies of 2,5, and 20 Hz to strips of medium-size arteries produced a frequency-dependent contraction that was reversed to a relaxation following treatment with phentolamine. Propranolol abolished the relaxation. In strips of dog coronary arteries of medium size, transmural stimulation elicited only a relaxation which was suppressed or reversed to a contraction by propranolol. Dog arteries of this size responded to norepinephrine and epinephrine with only a relaxation. It may be concluded that the quantity or the susceptibility of alpha-adrenoceptors is in the order of large greater than or equal to medium greater than small-size arteries from monkeys, whereas that of beta-adrenoceptors is in the order of medium = small greater than large arteries. Monkey coronary arteries appear to respond to endogenous and exogenous norepinephrine with a contraction more consistently than dog coronary arteries.
Effects of Epinephrine on Lipid Partition and Metabolism in the Rabbit
Authors: DURY ABRAHAM
Published: June 2012

Epinephrine overdosage in intact rabbits caused significant modifications in plasma lipid distribution and transport, and phospholipid metabolism of plasma, liver and aorta. Aortic phospholipid synthesis was accelerated shortly after epinephrine injection and persisted for 24 hours, but plasma and liver turnover rates were maximally elevated after 48 hours. Changes in plasma neutral fat concentration were paralleled by alterations in the levels of S
f
12-400 lipoproteins and a relationship between S
f
0-12 and plasma cholesterol levels is suggested by the data.
Relation of Negative Intraventricular Pressure to Ventricular Volume
Authors: BRECHER GERHARD A. , KISSEN ABBOTT T.
Published: June 2012

Elastic forces of the ventricular walls produce a subatmospheric (negative transmural) pressure in the empty quiescent ventricle of open chest dogs. As fluid is added to the ventricle the negative intraventricular trausmural pressures become 0 and finally positive. The resulting ventricular pressure-volume curves are S-shaped, having one limb in the negative and another in the positive pressure range. It is concluded that previously reported suction and negative intraventricular transmural pressures lasting throughout the entire diastole in ventricles with small residual volumes are caused by elastic forces which also prevail under static conditions.
Estimation of the Residual Volume of the Right Ventricle of the Dog's Heart
Authors: HOLT J. P. , ALLENSWORTH J. , Diana J. , Collins D. , Kines H.
Published: June 2012

The measurement of right ventricular end-diastolic volume, end-systolic volume, and stroke volume by means of the electric conductivity technic is described. The right ventricle empties in a "fractional" manner, as does the left ventricle, and on the average 39 per cent of its end-diastolic volume is ejected with each stroke, leaving a residual volume of 61 per cent.
Changes in Carbohydrate Metabolism of Cardiac and Striated Muscle in Hypothermic Rats
Authors: ITZHAKI S. , WERTHEIMER E.
Published: June 2012

The following represents a study of the influence of hypothermia on the carbohydrate metabolism of rat heart slices in comparison to rat diaphragm. The effect of thyroid on the induced metabolic changes in both types of muscle is investigated.
Effect of Synthetic Angiotonin on the Carotid Sinus
Authors: MCCUBBIN J. W. , PAGE IRVINE H. , BUMPUS F. MERLIN
Published: June 2012

Natural decapeptide or synthetic octapeptide angiotonin was ineffective in lowering arterial pressure or decreasing the carotid occlusion response when injected into the carotid sinus adventitia. Injection of synthetic octapeptide angiotonin into the lumen of the carotid sinus after tying its branches decreased the carotid occlusion response but the effect depended on dosage many times the pressor activity of 1 γ of norepinephrine which elicited a comparable effect.
Effective Frontal Plane Vectorcardiogram of
Rana Pipiens
Authors: BRODY DANIEL A.
Published: June 2012

A technic is described which provides highly accurate registration of the effective frontal plane vectorcardiogram of
Rana pipiens
. A comparative study with one of the conventional vectorcardiographic systems illustrates some of the inherent defects of the latter method. Another potentially useful aspect of effective vectorcardiograms is that they may be calibrated in a manner which presents heart vectors in their physically correct units of dimension.
Measurement of the Cardiac Output in Dogs by a Conductivity Method after Single Intravenous Injections of Autogenous Plasma
Authors: GOODWIN RICHARD S. , SAPIRSTEIN LEO A.
Published: June 2012

Equations are developed for the estimation of cardiac output from hematocrit dilution, using the continuously recorded conductivity of whole blood drawn from an artery through a conductivity cell, after a single intravenous injection of autogenous plasma. The equipment used is described, the results are compared with those of simultaneously performed measurements of dye dilution and the advantages of the method are discussed.
A Method Using Induced Waves to Study Pressure Propagation in Human Arteries
Authors: LANDOWNE MILTON
Published: June 2012

This report describes a method for utilizing externally induced impacts as a means of studying the propagation of pressure waves in intact human arteries. Because it is a new method its description is prefaced by a brief presentation of several factors relevant to wave propagation in living vessels; the description is followed by a critical evaluation.
Effects of Nicotinic Acid on Serum and Tissue Cholesterol in Rabbits
Authors: MERRILL JOSEPH M. , LEMLEY-STONE JANET
Published: June 2012

Studies reported in this communication showed that under the experimental conditions, nicotinic acid partially prevented a rise in serum cholesterol but effectively prevented cholesterol deposition in the aorta and, to a lesser extent, cholesterol storage in the liver.
Changes of Mean Spatial QRS and T Vectors and of Conventional Electrocardiographic Items in Hard Anaerobic Work
Authors: KAHN K. A. , SIMONSON E.
Published: June 2012

In 35 normal men, conventional and vectorial electrocardiographic items were studied after severe, anaerobic exercise over a recovery period of 8 min. The changes, especially of the T vector, are pronounced, but are different from those observed in coronary insufficiency. The hypothesis is advanced that the changes in anaerobic exercise are due to general myocarclial hypoxia, in contrast to the localized ischemia in coronary insufficiency.