bluuebunny/crossref_metadata_2025 huggingface dataset:
Estimation of open-loop gain of canine arterial pressure control system by a new method
Authors: Hosomi H. , Yokoyama K.
Published: December 2017

We developed a method to estimate an overall open-loop gain of the arterial pressure control system without surgically opening the reflex loop. Dogs anesthetized by intravenous injection of Nembutal (35 mg/kg body wt) were bled by 2 ml/kg body wt within 2-3 s through a catheter inserted into the abdominal aorta. Arterial pressure change after the quick hemorrhage was monitored via a catheter placed in the aortic arch for more than 2 min. The overall open-loop gain of the lumped arterial pressure control system was assessed as (delta API/delta APs)-1, where delta API is the immediate fall and delta APs the steady-state fall in mean arterial pressure obtained by a filter with a 2-s time constant. The advantage of this method is that the overall open-loop gain can be estimated under the closed-loop condition in which the baroreceptor reflexes operate naturally around the existing range of systemic arterial pressure. This enables one to study time-varying characteristics of the reflex gain. The disadvantage is that the substantial constituents of the lumped reflex system remain to be confirmed.
Norepinephrine effect on in situ venous membrane potential in spontaneously hypertensive rats
Authors: Harder D. R. , Contney S. J. , Willems W. J. , Stekiel W. J.
Published: December 2017

Comparative in situ (innervation and circulation intact) and in vitro measurements of transmembrane potential (Em) were made in vascular smooth muscle cells (VSM) of small (300-500 micrometers) veins of an externalized intestinal mesenteric loop in 13- to 15-wk-old anesthetized spontaneously hypertensive rats (SHR) and Wistar-Kyoto normotensive controls (WKY). During suffusion with physiological salt solution (PSS), the mean in situ Em in SHR was significantly lower (-34 +/- 0.8 mV) than in WKY (-49 +/- 1.3 mV). In situ neural blockade with 1 microgram/ml tetrodotoxin (TTX) in PSS hyperpolarized venous Em in SHR (-45 +/- 1.7 mV) but not in WKY. In vitro Em in SHR (-51 +/- 1.0 mV) and WKY (-54 +/- 1.1 mV), though significantly elevated above respective in situ values, did not differ significantly from each other and were not altered by TTX. Increasing norepinephrine (NE) concentrations in the PSS gradedly depolarized the venous VSM of WKY in situ to a plateau Em of -32 +/- 0.9 mV at 6 microM (1 micrograms/ml) NE but had no significant depolarizing effect on the less-polarized venous VSM of SHR. However, after addition of 1 micrograms/ml TTX to the PSS, the in situ Em in SHR followed a depolarizing NE dose-response curve similar to that observed in WKY (with or without TTX). These results support the hypothesis that the neurogenic vasoconstrictor component of VSM tone is significantly elevated in mesenteric veins of the SHR model of essential hypertension.
Transcapillary Starling pressures in the fetus, newborn, adult, and pregnant adult
Authors: Brace R. A. , Christian J. L.
Published: December 2017

We used the method of membrane osmometry to determine capillary pressure (Pc), plasma protein osmotic pressure (IIp), interstitial protein osmotic pressure (IIif), and interstitial free fluid pressure (Pif) in subcutaneous tissue. These pressures were measured in the sheep and guinea pig fetus, newborn, adult, and pregnant adult. Although there were some similarities, we found major species differences. 1) IIp was a minimum in the fetus and gradually increased to a maximum with adulthood in the guinea pig, whereas IIp attained adult values in the newborn lamb. 2) IIp and Pc did not change with pregnancy in sheep, but, in the guinea pig, IIp and Pc decreased by approximately 30% during pregnancy. 3) The maximum and minimum IIif occurred in the fetal and adult guinea pig, respectively, whereas this was reversed in the sheep. 4) IIif decreased with pregnancy in the guinea pig but not in the sheep. 5) The minimum Pif was found in the newborn of both species. These data suggest that the forces that determine the intravascular-interstitial fluid distribution are different in the fetus, newborn, and adult and also vary among species.
Role of renin-angiotensin system in response to hemorrhage in fetal sheep
Authors: Iwamoto H. S. , Rudolph A. M.
Published: December 2017

During fetal life, the autonomic nervous system is not fully mature, and it is likely that hormonal mechanisms play an important role in controlling cardiovascular function. In chronically instrumented fetal sheep, hemorrhage increased plasma renin activity and plasma angiotensin concentration significantly from 6.7 +/- 2.5 to 15.2 +/- 3.1 ng.ml-1.h-1 and from 74 +/- 19 to 182 +/- 43 pg/ml, respectively. Both mean arterial and venous blood pressures decreased initially from 45 to 35 Torr and from 3.5 to 2.5 Torr, respectively; then both returned to control values. Fetal heart rate decreased initially from 174 beats/min and then increased to 186 beats/min. To determine whether angiotensin had a role in mediating these responses to hemorrhage, we hemorrhaged a second group of fetuses before and during infusion of saralasin, a competitive antagonist of angiotensin. Hemorrhage during infusion of saralasin decreased heart rat from 170 to 145 beats/min and further decreased mean arterial pressure to 30 Torr. Cardiac output decreased from 436 +/- 25 to 368 +/- 30 ml.min-1.kg-1, and umbilical-placental blood flow decreased from 205 +/- 20 to 145 +/- 10 ml.min-1.kg-1. We conclude that the renin-angiotensin system plays a major role in the response to hemorrhage in fetal sheep.
Isovolumetric properties of ventricles of spontaneously hypertensive rats
Authors: Heller L. J.
Published: December 2017

Isovolumetric pressure-producing properties of isolated Langendorf-perfused hypertrophied ventricles from adult spontaneously hypertensive rats (SHR) were compared with those of nonhypertrophied ventricles from adult Wistar-Kyoto rats (WKY). SHR ventricles were found to produce greater systolic pressure than WKY ventricles when subjected to similar stimulation and perfusion conditions. Correction for the differences in ventricular mass eliminated the difference between groups. Apparent diastolic pressure at high stimulus rates was higher in SHR than WKY, and SHR developed exaggerated aftercontractions following cessation of high-frequency stimulation. Refractory periods of hypertrophied ventricles determined by paired-pulse stimulation were not found to be different from nonhypertrophied ventricles, but hyperexcitable periods of SHR ventricles were significantly longer than WKY ventricles. In addition, the intrinsic ventricular rate of SHR preparations was significantly greater than that of WKY.
Hand arterial blood flow responses to local venous congestion
Authors: Levy B. I. , Oliva Y. , Martineaud J. P.
Published: December 2017

Hand and forearm blood flows were measured in 12 subjects by means of a range-gated Doppler velocimeter, in basal conditions and after inflation (30, 50, 60, 70, and 90 mmHg) of a venous occlusion cuff on the middle part of the forearm. In basal conditions, there were significant decreases in radial, ulnar, and brachial blood flow after cuff inflation (up to -78, -69, and -31%, respectively). Minimal values were reached in less than 7 s. After occlusion of the circulation of the hand, control brachial blood flow was lowered but not significantly affected by venous distension. The results must be considered and accounted where venous occlusion plethysmography is used to measure segmental blood flow.
A servo-controlled roller pump for cardiovascular research
Authors: Mohrman D. E.
Published: December 2017

Page H269: D. E. Mohrman. “A servo-controlled roller pump for cardiovascular research.” Page H270: footnote 1 should read: For machine and assembly drawings necessary to duplicate this pump, order NAPS Document 03826 from Microfiche Publications, P.O. Box 3513, Grand Central Station, New York, NY 10017.
Effects of hyperkalemia and glycoside on thallium exchange in rabbit ventricle
Authors: Krivokapich J. , Shine K. I.
Published: December 2017

Page H612: J. Krivokapich and K. I. Shine. “Effects of hyperkalemia and glycoside on thallium exchange in rabbit ventricle.” Page H617: column 1, line 2: 0.545 should read 0.0545.
Methods for isolation, cannulation, and in vitro study of single microvessels
Authors: Duling B. R. , Gore R. W. , Dacey R. G. , Damon D. N.
Published: December 2017

A method is described for the isolation and cannulation of microvessels (12-112 micrometers) that permits study, in vitro, of their physiology and pharmacology. Vessels from the hamster cheek pouch, testis, and mesentery and from rat brain have been isolated at 4 degrees C with specially prepared instruments and viewed with an inverted microscope. The vessels were cannulated at one end by equipment developed for renal tubular perfusion. The uncannulated end of the vessel is sealed, and experiments on reactivity and mechanics are carried out at fixed intravascular pressures. The isolated microvessels studied have a modulus of elasticity that is consistent with that observed in large vessels, and they display similar maximal active tension development (approximately 10(6) dyn/cm2). Reactivity to norepinephrine, acetylcholine, and adenosine are in the normal range for microvessels. Spontaneous tone is present, as evidenced by stable tonic contractions as well as phasic contractions in the frequency range of 3-30/min. The vessels display stress activation (myogenic response) consisting of contraction in response to increased intraluminal pressure. Our findings suggest that this preparation will be very useful in elucidating the physiology and pharmacology of the resistance vessels in the terminal vasculature.
Short time constant for rate-dependent changes of atrioventricular conduction in dogs
Authors: Billette J.
Published: December 2017

The number of short cardiac cycles necessary to induce, and normal cycles to dissipate, a rate-dependent shortening in atrioventricular (AV) nodal functional refractory period (FRP) and conduction time (CT) was determined in six anesthetized dogs. For the induction study, the periodic premature stimulation procedure was performed at control and repeated six times while 1, ..., 6 conditioning short prepremature cycles (PPC) were introduced between the last basic cycle and the premature cycle. In all dogs, FRP was maximally shortened and the recovery curve was maximally shifted to the left when the premature cycle was preceded by 1 PPC. Adding 2, ..., 6 PPC resulted in slightly fewer but persistent shortenings of both FRP and CT. The dissipation of the FRP and CT shortenings produced by 2 and 6 PPC was studied subsequently in the same dogs by introducing 1, ..., 6 normal basic cycles between the last PPC and the test premature cycle. The FRP and CT shortenings induced by 2 or 6 PPC were almost completely dissipated after one normal basic cycle. Thus, one short cycle produces a maximum shortening in AV nodal FRP and CT, and one normal basic cycle is sufficient to dissipate these effects.
Central shunt flows and pressures in the mature fetal lamb
Authors: Anderson D. F. , Bissonnette J. M. , Faber J. J. , Thornburg K. L.
Published: December 2017

Two to eight days after surgery, we determined biventricular cardiac output with the microsphere-dilution method and individual ventricular output with an electromagnetic flow sensor in 12 fetal lambs. Mean biventricular output was 462 ml.min-1.kg-1. Right ventricular output was 60%, pulmonary blood flow was 6%, blood flow in the ductus arteriosus was 54%, flow through the foramen ovale was 34%, and flow in the descending thoracic aorta above the ductus arteriosus was 12% of the biventricular cardiac output. Foramen ovale flow did not correlate with the pressure difference between the atria. The flow though the foramen ovale correlated positively with the flow in the inferior caval vein. It was concluded the shunt flow through the foramen ovale is mainly determined by the kinetic energy of the blood in the "lower atrial inflow tract." Fetal systemic somatic blood flow showed a reliable negative correlation with the oxygen tension in the fetal arterial blood. This was taken as presumptive evidence for long-term autoregulation of flow in the peripheral tissues.
Protein phosphorylation in cardiac and vascular smooth muscle
Authors: Barany M. , Barany K.
Published: December 2017

In the heart and arterial smooth muscles, several proteins are phosphorylated. This review summarizes our current knowledge about these phosphoproteins and their possible role in the function of these muscles. In the contractile apparatus, the phosphorylation of myosin light chain seems to be an integral part of the contraction cycle of arterial smooth muscle. However, in the heart the relationship between light chain phosphorylation-dehosphorylation and systolic-diastolic states remains open. In the heart, the phosphorylation of the inhibitory subunit of troponin, a myofibrillar protein, parallels the positive inotropic response induced by beta-adrenergic agonists. It seems likely that this phosphorylation is involved in the physiological stimulation of the heart by epinephrine. Cardiac sarcoplasmic reticulum contains a low-molecular-weight protein, phospholamban, the phosphorylation of which is required for Ca2+ transport. Ion fluxes through the heart sarcolemma may also be controlled through membrane protein phosphorylation. Key enzymes of the energy-yielding pathways in the heart, the pyruvate dehydrogenase multienzyme complex and phosphorylase, are turned on and off by phosphorylation-dephosphorylation mechanisms. Our understanding of protein phosphorylation in the heart has advanced greatly. In contrast, with the exception of the myosin light chain, much less is known about the many proteins phosphorylated in arterial smooth muscle.
Sources of activator calcium in rabbit basilar artery
Authors: McCalden T. A. , Bevan J. A.
Published: December 2017

The responses of segments of rabbit basilar and ear arteries to high K+ (K+, 45 mM), norepinephrine (NE, 10(-5) and 10(-7) M), and 5-hydroxytryptamine (5-HT, 10(-7) M) were tested before and after their incubation in calcium (Ca2+)-free Krebs solution for times varying from 2.5 to 60 min. The time course of evolution of the responses to K+ with Ca2+-free conditions in both vessels could be represented by a monoexponential curve. The rates of decline of the responses of amines in the ear artery were similar to K+ at first but then fell off at a slower rate. The decline in K+ contraction and the fast initial decline of the NE contraction may relate to the speed of removal of extracellular calcium, whereas the final slower NE decline reflects depletion of an intracellular pool. In the basilar artery, the NE and K+ response declined in a similar manner, whereas the 5-HT contraction showed a fast and a slow component of decline. These results for the maintained agonist response were confirmed using the Ca2+ influx antagonist, 3-methoxyverapamil (D 600). In addition, a D 600-insensitive phasic contraction was observed in both arteries. These results suggest that the steady-state NE contraction in the basilar artery is almost entirely dependent on loosely bound extracellular Ca2+. This is in contrast to the ear artery, where an additional tightly bound or intracellular Ca2+ pool is used. This source is present in the basilar artery but contributes only to a D 600-insensitive phasic component.
Unaltered membrane properties of arterial muscle in Dahl strain genetic hypertension
Authors: Abel P. W. , Trapani A. , Matsuki N. , Ingram M. J. , Ingram F. D. , Hermsmeyer K.
Published: December 2017

To characterize membrane properties of arterial muscle from Dahl strain hypertensive rats, we measured caudal artery contractile sensitivity to norepinephrine and serotonin, membrane potential at 16 and 37 degrees C, and intracellular potassium, sodium, and chloride content. Dahl salt-resistant (R) strain fed low- or high-salt diets and Dahl salt-sensitive (S) strain fed a low-salt diet remained normotensive. The Dahl S strain on high-salt diets became hypertensive after 4 wk of high salt feeding. There was no significant difference in the norepinephrine or serotonin effective concentration (EC) EC50, EC10, or maximum response between the hypertensive and any of the three normotensive groups. Membrane potential measured at 37 and 16 degrees C and electron-probe analysis of intracellular potassium, sodium, and chloride concentration showed no significant differences between the four groups of animals. These results that arterial muscle membrane mechanisms are not altered in genetically hypertensive Dahl salt-sensitive rats.
Effect of stretching the superior vena cava on heart rate in rats
Authors: Kaufman S. , Mackay B. , Kappagoda C. T.
Published: December 2017

The effect on the heart rate of stretching the superior vena cava 3-4 mm above its entrance to the right atrium was examined in rats anesthetized with chloralose. The superior vena cava was stretched 41 times in 16 rats. There was a mean increase of 24.1 +/- 1.9 (SE) beats/min. This response was abolished (6 rats) by sympathetic blockade (with propranolol hydrochloride and bretylium tosylate) and by bilateral vagosympathectomy (5 rats). Application of lidocaine to the cervical vagi also abolished the response in a reversible manner (4 rats). In five rats, histological examination of the superior vena cava revealed an abundance of nerves, which formed a net in the stretched region. Complex unencapsulated nerve endings similar to those demonstrated in the dog and cat were not found.
Production of chronic heart block in closed-chest dogs: an improved technique
Authors: Randall O. S. , Westerhof N. , Van den Bos G. C. , Sipkema P.
Published: December 2017

Chronic complete heart block was produced in 38 closed-chest anesthetized dogs with a special cannula introduced via a jugular vein. A Formalin mixture (0.2-1.0 ml, consisting of equal amounts of 40% Formalin and radiopaque material) was injected through this cannula into the His bundle, which was located with a His-bundle catheter. The entire procedure took approximately 30 min and was successful in 90% of the cases.
Microvascular adaptations during maturation of striated muscle
Authors: Sarelius I. H. , Damon D. N. , Duling B. R.
Published: December 2017

It is well known that capillary density in striated muscle changes during maturation. Capillary density is an important determinant of tissue oxygen supply, the other principal determinants being capillary erythrocyte flow and capillary hematocrit. The microcirculation of the hamster cremaster muscle was studied at different stages of development. We found that the microcirculation of juvenile animals was characterized by small intercapillary distances, short capillary lengths, and tortuous vessels. During maturation, the capillaries elongated and developed the more “typical” parallel pattern. Capillary density decreased from 1,626 +/- 60 capillaries . mm-3 at 35 days of age to 696 +/- 65 capillaries . mm-3 at 132 days; erythrocyte flow per capillary decreased from 1,441 +/- 135 to 583 +/- 47 micrometers 3 . s-1; and capillary hematocrit decreased from 21.5 +/- 0.7 to 14.6 +/- 0.6%. Concomitant with these decreases, the functional reserve increased; in adult muscles, capillary density could increase by 42%, erythrocyte flow per capillary by 457.2%, and capillary hematocrit by 112.4%, compared with 7.7, 20.3, and 24.1%, respectively, in immature animals. These observations show that age significantly modifies microvascular parameters related to tissue oxygen supply and provides an explanation for some conflicting observations in the literature.
Criteria for adequate oxygenation of isometric kitten papillary muscle
Authors: Paradise N. F. , Schmitter J. L. , Surmitis J. M.
Published: December 2017

Papillary muscles were taken from the right ventricles of hearts excised from chloroform-anesthetized kittens. Progressive 100-mmHg stepwise decreases in superfusate oxygen partial pressure (PO2) from control (95% O2 aeration, PO2, 620-650 mmHg) were produced, and subsequent changes in isometric active and resting tension were measured. If, under a given set of experimental conditions, the initial decrement in PO2 produced no decrease in active tensions development, it was concluded that complete oxygenation of the entire muscle cross section was achieved when bath PO2 was maximal. Accordingly, adequate muscle oxygenation during 95% O2 aeration occurred when temperature, stimulation rate, and mean muscle diameter were, respectively, 1) 37 degrees C, 30 beats/min, and 0.89 +/- 0.06 mm; 2) 30 degrees C, 30 beats/min, and 0.94 +/- 0.02 mm; and 3) 30 degrees C, 12 beats/min, and 1.15 +/- 0.09 mm. On the other hand, adequate oxygenation at either 30 or 37 degrees C was not demonstrable when rate was 60 beats/min and muscle diameter exceeded 0.60 mm. We conclude that very low stimulation rates are required for oxygen sufficiency unless the papillary muscle is extremely thin.
Comparison of fast and slow pressor effects of angiotensin II in the conscious rat
Authors: Brown A. J. , Casals-Stenzel J. , Gofford S. , Lever A. F. , Morton J. J.
Published: December 2017

Female Wistar rats were infused intravenously with 5% dextrose for 3 days, then with angiotensin II (ANG II) in 5% dextrose at 20 ng . kg-1 . min-1 for 7 days, and finally with dextrose for 2.5 days. ANG II raised mean arterial pressure (MAP) gradually; by the 7th day it was 49.7 mmHg higher than during the dextrose control period in the same rats. Control rats were infused with dextrose for 12.5 days; MAP did not change. Plasma ANG II concentration was measured during infusion. In hypertensive rats on the 7th day of ANG II infusion, it was six times higher than in control rats infused with dextrose. Changes of blood pressure and plasma ANG II concentration were compared in further rats infused with much larger doses of ANG II. Rats receiving 270 ng . kg-1 . min-1 for 1 h had an almost maximal direct pressor response, MAP rising 45.3 mmHg and plasma ANG II rising 32-fold compared with controls. Thus, infusion of ANG II at low dose without direct pressor effect gradually raises blood pressure to a level similar to the maximum direct pressor effect produced by larger doses of ANG II. Sodium balance and food and water intakes were also measured and did not change during prolonged infusion of ANG II at 20 ng . kg-1 . min-1. Thus, the slow pressure effect of ANG II develops at a lower and more nearly physiological plasma concentration of the peptide than do the direct pressor effect and the effects on drinking, eating, and urinary sodium excretion.
Effects of insulin on ventricular function in diabetic lambs with acidosis
Authors: Downing S. E. , Lee J. C. , Werner J. C.
Published: December 2017

Diabetes mellitus (DM) was induced in 10 lambs by giving alloxan (150 mg/kg). Two to 4 days later, mean values for glucose were 748 mg/dl, and for arterial pH 7.25 (acute group). Two additional lambs were studied after 3 mo of DM (chronic group). Data were compared with 7 controls (glucose 128 mg/dl, pH 7.36). Left ventricular (LV) performance was assessed from function curves and measurements of LV dP/dtmax. Stroke volume ejected at LV end-diastolic pressure of 5 cmH2O (SV5) was calculated from regression analysis of each curve. SV5 averaged 2.83 +/- 0.34 ml in controls and 2.90 +/- 0.23 ml in the acute diabetics (not significant). Mean values for LV dP/dtmax also did not differ. A significant correlation was found between SV5 and LV weight (P less than 0.001). SV5 was normalized as ml/100 g LV, and average values for the three groups were identical. Insulin (10 U/kg) caused a progressive fall in SV5 in diabetics with severe acidosis (pH 7.00), but not in those with less acidosis (pH 7.28). In nondiabetics given lactic acid (pH 7.01), SV5 fell to 60% of initial values 1 h after insulin. Acidemic animals not given insulin showed no reduction in LV performance in the same time interval. Adrenergic support is necessary to prevent cardiac failure associated with acidosis. The present findings are ascribed to inhibition by insulin of catecholamine inotropic action on myocardium.
Effect of microsphere size on apparent intramural distribution of intestinal blood flow
Authors: Maxwell L. C. , Shepherd A. P. , Riedel G. L. , Morris M. D.
Published: December 2017

Microspheres were used in earlier studies to determine the distribution of blood flow within the intestinal wall, but the selection of microsphere size was not systematic. In one study, a 5-micrometers difference in mean diameter markedly altered the submucosal vs. mucosal distribution of microspheres. Therefore, we examined the effect of size on microsphere distribution within the gut wall. Loops of canine small bowel were perfused at constant pressure, and microspheres were injected in the following order: 9 +/- 1, 15 +/- 1, and 26 +/- 2 micrometers. Gut segments were separated into mucosal, submucosal, and muscularis tissues. The microspheres were recovered from digested tissues and venous blood. The number and diameter of spheres in an aliquot of resuspended spheres were determined by digital image analysis. The ratio of mucosal to submucosal accumulation varied 60-fold for sphere diameters from 8 to 20 micrometers. The muscularis' share did not vary systematically with sphere size. Approximately 20% of spheres less than 11 micrometers reached venous blood, whereas few (less than 1%) of larger sizes did. We conclude: 1) sphere distribution within the gut wall is size dependent, 2) correction for microsphere shunting will be difficult, because the route taken by untrapped spheres is unknown, and 3) fractionating intramural flow among the three layers is not practical with commercially available spheres. However, under control conditions 15-micrometers spheres seem to distribute independently of size between muscularis and a lumped mucosal-submucosal compartment.
Evidence for circulating factors as a cause of venous hypertrophy in spontaneously hypertensive rats
Authors: Greenberg S. , Gaines K. , Sweatt D.
Published: December 2017

Increased contractility, decreased extensibility, and hypertrophy occur in portal veins (PV) obtained from spontaneously hypertensive rats (SHR). This study evaluates the potential existence of circulating humoral factors as mediators of these changes. SHR were parabiosed with normotensive Wistar-Kyoto rats (WKY) matched for sex and age. Blood pressure increased over a 3-wk to 5-mo period in 2-mo-old WKY parabiosed with SHR. Similar changes were absent in WKY parabiosed with WKY (WKY-WKY) or in SHR parabiosed with SHR (SHR-SHR). The functional blood flows between the parabiosed pairs were 1.4 +/- 0.21%. PV obtained from WKY-WKY developed less spontaneous tension, less tension in response to norepinephrine, potassium chloride, angiotensin II, an 9 alpha, 11 alpha-epoxymethano-prostaglandin H2, and were more extensible than PV obtained from SHR-SHR. In contrast, PV obtained from the WKY member of the WKY-SHR, developed changes similar to PV obtained from the SHR. The wet and dry weight and protein content increased in the PV of WKY-SHR, when compared with these parameters in the PV obtained from WKY-WKY. Light microscopy of the blood vessels demonstrated that PV obtained from the wKY parabiosed to SHR exhibited medial smooth muscle hypertrophy. These data support the conclusion that a circulating humoral factor in the SHR may initiate the venous smooth muscle derangements during the development of spontaneous hypertension.
Effects of carnitine and atractyloside on canine cardiac electrical activity
Authors: Gilmour R. F. , Williams E. S. , Farmer B. B. , Zipes D. P.
Published: December 2017

It has been proposed that electrophysiological changes following coronary artery occlusion result from inhibition of the adenine nucleotide translocase and that these changes can be reduced by carnitine infusion or reproduced by infusion of K+-atractyloside. In the present study, we recorded bipolar electrograms during serial 3- to 5-min occlusions of the left anterior descending coronary artery in open-chest, anesthetized dogs. DL-Carnitine (100-200 mg/kg iv) prior to coronary artery occlusion did not significantly alter ischemia-induced electrogram changes. L-Carnitine (100 mg/min ia) distal to the site of occlusion during coronary artery occlusion partially reversed ischemia-induced electrogram changes, but these effects resembled those produced by intra-arterial infusion of NaCl. During normal perfusion, intra-arterial infusion of K+-atractyloside (750 mumol/10 min) or equimolar KCl produced similar reversible flattening of perfused zone electrograms. Sodium atractyloside (750 mumol/10 min ia) did not produce electrogram changes. We conclude that 1) carnitine does not attenuate ischemia-induced electrogram changes in this model and 2) K+-atractyloside-induced electrogram changes are primarily due to K+.
Effects of central venous blood volume shifts on arterial baroreflex control of heart rate
Authors: Billman G. E. , Dickey D. T. , Teoh K. K. , Stone H. L.
Published: December 2017

The purpose of this study was to investigate the effects of anesthesia, body position, and blood volume expansion on baroreflex control of heart rate. Five male rhesus monkeys (7.0-10.5 kg) were given bolus injection of 4.0 micrograms/kg phenylephrine during each of the following situations: awake sitting, anesthetized (AN) (10 mg/kg ketamine-HCl) sitting, AN recumbent, AN 90 degrees head down tilt, and AN 50% blood volume expansion with normal saline. beta-Receptor blockade was also performed on each treatment after anesthesia. Four additional animals were similarly treated after 20% blood volume expansion. R-R interval was plotted against systolic aortic pressure, and the slope was determined by linear regression. Baroreflex slope was significantly (P less than 0.05) reduced by 90 degrees head down tilt and 50% volume expansion both before and after beta-receptor blockade. A similar trend was seen after 20% volume expansion. These data are consistent with the thesis that baroreflex control of heart rate is reduced by central blood volume shifts.
Voltage dependence of digitalis afterpotentials, aftercontractions, and inotropy
Authors: Wasserstrom J. A. , Ferrier G. R.
Published: December 2017

The effects of membrane potential on digitalis-induced oscillatory afterpotentials (OAP) and aftercontractions (AC) were investigated in isolated canine false tendons and canine and feline papillary muscles. Transmembrane potential and contractions were measured simultaneously. Membrane potential was varied by current applied through an extracellular pipet. The amplitudes of OAP and AC induced by acetylstrophanthidin (0.5-1.0 X 10(-7) g/ml) or actodigin (0.5-1.0 X 10(-6) g/ml) were increased by depolarization and decreased or abolished by hyperpolarization in all tissues. Prior to the appearance of OAP and AC in preparations exposed to the drugs, depolarization caused both phenomena to appear. As in muscle, the strength of beats superimposed on the ascending limb of AC was potentiated, and the strength of beats superimposed on the relaxation phase was depotentiated. When the amplitude of AC was decreased by hyperpolarization, both potentiation and depotentiation were diminished. This effect was accompanied by a partial reversal of the changes induced by acetylstrophanthidin in the course of restitution of contractility and the configuration of the force-frequency relation.
Limitations of postextrasystolic potentiation in identifying ischemic myocardium
Authors: Cornish A. L. , Hanley H. G. , O'Connor W. , Slack J. D. , Patrick T. A. , Cole J. S.
Published: December 2017

To evaluate the usefulness of postextrasystolic potentiation in differentiating ischemic yet viable myocardium from infarcted myocardium, 20 dogs were chronically instrumented with left ventricular pressure gauges, left circumflex coronary artery flow probes, occluders, pacing wires, and ultrasonic segment-length transducers. Ten dogs had acute (1 h) coronary occlusions followed by reperfusion (4 days) and were then killed. Ten more dogs had more prolonged (1 mo) occlusions and were then killed. Timed premature ventricular contractions were induced, and the postextrasystolic beat was evaluated. In ischemic segments that were hypokinetic, postextrasystolic potentiation of shortening occurred in both groups. In ischemic segments that were akinetic or dyskinetic, potentiation of shortening did not occur in either group. Both groups showed recovery of shortening, and histologically normal myocardium was identified in the region between the segments in all animals. Thus, akinetic and dyskinetic segments did not show postextrasystolic potentiation of shortening, even though the tissue was viable and showed functional recovery. Failure to improve shortening after a premature ventricular beta in an ischemic segment does not necessarily indicate nonviable myocardium.
Hypoxic responses of sympathetic preganglionic neurons in the acute spinal cat
Authors: Rohlicek C. V. , Polosa C.
Published: December 2017

The relation between arterial O2 tension (PaO2) and the firing rate of sympathetic preganglionic neurons (SPN) of the cervical sympathetic trunk was studied during graded isocapnic hypoxia and hyperoxia in unanesthetized acute C-1 spinal cats. In the PaO2 range between 40 and 400 Torr there was no relation between the two variables. Below 40 Torr firing rate increased as PaO2 decreased, reaching an average peak value of ten times control at a PaO2 of 20 Torr. Mean arterial blood pressure (MABP) was also independent of PaO2 between 40 and 400 Torr and increased by an average of 25% at PaO2 values below 40 Torr. Intravenous administration of hexamethonium or phentolamine abolished the MABP response but not the SPN response to hypoxia. Pentobarbital (5-60 mg/kg iv) did not modify the SPN response to hypoxia, although normoxic SPN background firing was considerably depressed. The excitatory effect of hypoxia seems independent of excitatory afferent input and appears to be a general property of SPN.
Hydrostatic forces limit swelling of rat ventricular myocardium
Authors: Pine M. B. , Brooks W. W. , Nosta J. J. , Abelmann W. H.
Published: December 2017

To study ventricular cellular volume regulation when cell membranes and ion pumps cannot prevent swelling, rat ventricular sections were incubated in modified Krebs-Henseleit solutions in which 1) potassium was substituted for sodium, ion for ion; or 2) sodium chloride was reduced to decrease osmolarity to 228, 171, or 114 mosM. Ventricular water, [3H]inulin and [3H]mannitol spaces, potassium, sodium, chloride, and protein contents, and resting transmembrane potentials were measured. Increases in ventricular cellular volume were less than 30% in potassium-substituted and extremely dilute media (114 mosM), in contrast to increases of over 100% in identically treated renal cortical slices. In potassium-substituted solution, the fluid gained by ventricular cells during incubation was hypertonic with respect to the bathing medium. In dilute solution (171 and 114 mosM), ventricular, cellular, and extracellular osmolarities equilibrated only after substantial losses of cellular ions had occurred. These findings support the existence of mechanical limitations to ventricular cellular swelling, which may be caused by a unique network of interstitial collagen present in ventricular myocardium.
Multiple mechanisms of reactive hyperemia in arterioles of the hamster cheek pouch
Authors: Lombard J. H. , Duling B. R.
Published: December 2017

To investigate mechanisms of reactive hyperemia, single arterioles of the hamster cheek pouch were occluded for periods of 1 s-3 min. Arteriolar diameters were measured upstream and downstream from the occlusion. O2 availability to the tissue was controlled by equilibrating the suffusate with low (0% O2) or high (10% O2) O2 gas mixtures. After very brief occlusions downstream sites dilated transiently, but upstream diameters did not change. Upstream and downstream diameters both increased during longer occlusions with O%-O2 and 10%-O2 suffusion. Microvascular pressure decreased at downstream sites and increased at upstream sites within 1-2 s of occlusion. During 0%-O2 suffusion tissue and periarteriolar O2 tensions (PO2's) began to decrease within 2 s of occlusion and had decreased halfway to their minimum value by 7 s. PO2's decreased only slightly during 10%-O2 suffusion. Calculated first-order rate constants for arteriolar diameter recovery decreased and total recovery time increased as occlusion duration was prolonged. This study suggests that multiple mechanisms (metabolic, myogenic, and passive) contribute to reactive hyperemia.
Perinatal pulmonary prostaglandin production
Authors: Leffler C. W. , Hessler J. R.
Published: December 2017

Products of reactions catalyzed by prostaglandin cyclo-oxygenase [prostaglandins (PG), thromboxanes] were analyzed by gas chromatography with electron-capture detection in the venous effluents of in situ Krebs-perfused lungs of exteriorized fetal goats and sheep before and after ventilation with air. The major products were 6-keto-PGF1 alpha and 6,15-diketo[13,14-dihydro] PGI2 without blood components. After ventilation, which decreased pulmonary vascular resistance to 63% of the before-ventilation value, lung production of 6-keto-PGF1 alpha and metabolite increased 50 and 230%, respectively. These data, in addition to earlier findings of inhibition of ventilation-induced pulmonary vasodilation by indomethacin and increased net production of PG-like material after ventilation of blood-perfused fetal lungs, support the hypothesis that ventilation of fetal lungs with air at birth increases synthesis of PGI2 by or near pulmonary resistance vessels, resulting in high local concentrations of PGI2 near its site of production. PGI2 appears to be important in the pulmonary vascular resistance decrease that is necessary for successful perinatal transition.
Reflex control of canine hindlimb resistance under different modes of perfusion
Authors: Cox R. H. , Bagshaw R. J.
Published: December 2017

The carotid sinus control of hindlimb hemodynamics was determined in halothane-anesthetized vagotomized dogs. The carotid sinuses were bilaterally isolated and perfused under controlled conditions. The hindlimb was perfused under conditions of 1) physiological inflow, 2) constant pressure, and 3) constant flow. The variation of hindlimb resistance with mean carotid sinus perfusion pressure was largest under conditions of constant-pressure perfusion and smallest with physiological inflow. Values for constant-flow perfusion were intermediate. The effects of different values of constant-flow perfusion on the carotid sinus control of hindlimb hemodynamics was also determined. Values of hindlimb resistance increased with decreasing flow rate as did the variation with carotid sinus perfusion pressure. No evidence of a contribution of local control mechanisms related to changes in perfusion pressure or bed inflow could be demonstrated. The differences in the variation of hindlimb resistance with carotid sinus pressure under the various perfusion conditions can be explained on the basis of the mechanics of vascular smooth muscle. The amount of lumen constriction associated with changes in degree of activation depends on the conditions under which shortening occurs as well as upon the initial muscle length. It appears that local factors do not contribute to the control of hindlimb hemodynamics under the conditions in which these studies were performed.
The design of the normal aortic valve
Authors: Thubrikar M. , Piepgrass W. C. , Shaner T. W. , Nolan S. P.
Published: December 2017

The design parameters of the natural aortic valve in vivo were not known, which may explain why various bioprosthetic valves have been designed differently. The design of the aortic valve was studied in vivo by placing radiopaque markers in the valve. The marker movement revealed that, during a cardiac cycle, the design parameters of the valve were changing continuously with changing aortic pressure and ventricular geometry. During diastole decreasing radius of the commissures (Rc) and increasing radius of the bases (Rb) caused the leaflets to tilt toward the ventricle, thereby decreasing the bottom surface angle (alpha) and increasing the free-edge angle (phi) of the leaflet. During systole Rc increased, Rb decreased, and interleaflet distance decreased, causing a change in the geometry of the open valve from conical to cylindrical. In middiastole the design parameters were Rb/Rc = 1.2, H/Rc = 1.4, phi = 34 degrees, and alpha = 20 degrees, where H is sinus height. How a significant deviation from the design could compromise the efficiency and longevity of the valve is discussed.
Rapid resetting of the carotid baroreceptor reflex in the cat
Authors: Kunze D. L.
Published: December 2017

The carotid baroreceptor depressor reflex of the chloralose-anesthetized cat was examined to determine the role of the prevailing carotid pressure in determining the threshold, gain, and range of operation of the reflex response. After the pressure of an isolated perfused carotid sinus was held at 80 mmHg for 20 min the threshold pressure necessary to elicit the reflex systemic blood pressure response was 78 +/- 2.9 (SE) mmHg (n = 5). When carotid pressure was maintained for 20 min at 120 and 160 mmHg the threshold rose to 113 +/- 2.9 and 126 +/- 3.0 mmHg, respectively. The resetting of the threshold to a stable value upon elevating or reducing carotid sinus pressure was accomplished within 15—;20 min. The entire range of operation of the reflex response was shifted to higher carotid pressures as the holding pressure was elevated. The midrange gain of the response was unchanged at the three holding pressures tested. These findings indicate that the carotid baroreceptor reflex need not operate over a fixed range but that the range may be rapidly adjustable to the prevailing pressure. When arterial pressure is sustained at a level that is elevated or depressed from normal the carotid baroreceptor reflex acutely resets to operate in the range of the prevailing pressure with a threshold that has moved toward the prevailing pressure.
Effect of oxygen on blood flow autoregulation in cat sartorius muscle
Authors: Sullivan S. M. , Johnson P. C.
Published: December 2017

To assess the role of O2 in blood flow autoregulation, arteriolar diameter and erythrocyte velocity were measured in individual microvessels of the cat sartorius muscle while ambient O2 tension (PO2) and perfusion pressure were altered. The muscle surface was covered with a layer of silicone fluid equilibrated with a gas mixture containing 0—20% O2. Under control conditions (0% O2) all except the largest arterioles dilated with pressure reduction, and all showed significant blood flow autoregulation. Elevated PO2 diminished flow regulation and dilation in large and small arterioles when arterial pressure was reduced. This effect was generally more pronounced in the small arterioles where elevated PO2 caused complete cessation of blood flow. Complete blood flow stoppage was not routinely seen in larger vessels and may reflect the fact that these vessels also supply deeper tissue regions less affected by the change in ambient PO2. Our results indicate that the PO2 level of the tissue may be an important determinant in blood flow autoregulation.
Anesthesia and microvascular dynamics in spontaneously hypertensive rats
Authors: De Lano F. A. , Zweifach B. W.
Published: December 2017

Studies on pressure dynamics in rats under local anesthesia were carried out to provide background information for subsequent intravital analysis of microvascular behavior in a skeletal muscle. An alpha-chloralose-urethan mixture (1:13.3%) was selected as the general anesthesia having the least effect on systemic pressures in spontaneous hypertensive (SHR) as well as normotensive (WKY), Sprague-Dawley and Wistar-Kyoto rats. Anesthetic agents, in general, lower systemic blood pressure in SHR by 30—50 mmHg and thereby distort microcirculatory flow and blood vessel-diameter relationships. Insertion of a plastic catheter into the trachea of the anesthetized rat, to maintain an open airway, had a complex effect on heart rate and systemic blood pressure and left the pressure in an unstable state. Severity of the change depended on the age of the rat and the anesthetic agent; hypertensive animals were especially vulnerable.
Hyperosmotic NaCl and severe hemorrhagic shock: role of the innervated lung
Authors: Lopes O. U. , Pontieri V. , Rocha e Silva M. , Velasco I. T.
Published: December 2017

Infusions of hyperosmotic NaCl (2,400 mosmol/l; 4 ml/kg) were given to dogs in severe hemorrhagic hypotension by intravenous injection (72 expts) or intra-aortic injection (25 expts). In 46 experiments intravenous infusions were given during bilateral blockage of the cervical vagal trunks (local anesthesia or cooling). Intravenous infusions (without vagal blockade) restore arterial pressure, cardiac output, and acid-base equilibrium to normal and cause mesenteric flow to overshoot prehemorrhage levels by 50%. These effects are stable, and indefinite survival was observed in every case. Intra-aortic infusions of hyperosmotic NaCl produce only a transient recovery of arterial pressure and cardiac output but no long-term survival. Intravenous infusions with vagal blockage produce only a transient recovery of cardiac output, with non long-term survival. Measurement of pulmonary artery blood osmolarity during and after the infusions shows that a different pattern is observed in each of these three groups and strongly indicates that the first passage of hyperosmotic blood through the pulmonary circulation at a time when vagal conduction is unimpaired is essential for the production of the full hemodynamic-metabolic response, which is needed for indefinite survival.
A technique for freeze fracturing minute amounts of isolated cardiac membrane
Authors: Shibata Y. , Manjunath C. K.
Published: December 2017

Electron microscopy (EM) of freeze-fractured membranes provides more information about internal membrane structure than EM of thin-sectioned or negatively stained material. However, it has heretofore been impractical to use freeze fracture routinely for analysis of highly purified membrane fractions obtainable in small (micrograms) amounts, because the technique, when conventionally applied to minute pellets, yields only one fracture of unpredictable quality; it also precludes in parallel biochemical studies by using up the entire preparation. To solve this problem, we have developed a method for freeze fracturing tiny droplets of suspended membranes containing 1-10 micrograms membrane protein, thereby allowing both multiple fractures and biochemical studies. Before fracture, the final membrane fractions can be concentrated, subjected to experimental manipulations, cross-linked, and glycerinated in a dialysis bag. The technique is illustrated on isolated gap junctions from rabbit hearts, which were chosen because their unique internal membrane structure allows unequivocal identification of membrane type based on structural criteria.
Corrigenda
Authors: Yellin E. L. , Peskin C. , Yoran C. , Koenigsberg M. , Matsumoto M. , Laniado S. , McQueen D. , Shore D. , Frater R. W. M.
Published: December 2017

Page H389: E. L. Yellin, C. Peskin, C. Yoran, M. Koenigsberg, M. Matsumoto, S. Laniado, D. McQueen, D. Shore, and R. W. M. Frater. “Mechanisms of mitral valve motion during diastole.” H398: text following Eq. 2 should read: In the absence of a pressure difference, flow is seen to decay exponentially to zero, i.e., the inertial energy imparted to the blood during early rapid filling is dissipated by viscous forces. This situation is illustrated in Figs. 2, 5, and 6. Under the second condition Listed above, we cannot solve Eq. 1 without a precise knowledge of ΔP( t), but one can readily predict that flow will decelerate more rapidly to zero (Figs. 1, 4). We do not yet have definitive evidence, but it is our thinking at this time that condition 1 is normal and that condition 2 occurs under situations that lead to a rapid rise in ventricular stiffness, e.g., rapid inflow into a large end-systolic volume.