bluuebunny/crossref_metadata_2025 huggingface dataset:
Effects of prostaglandins E1, E2, and F2alpha on uterine blood flow in nonpregnant sheep
Authors: Resnik R. , Brink G. W.
Published: December 2017

The effects of prostaglandins E1, E2, and F2alpha (PGE1, PGE2, and PGE2alpha, respectively) on uterine blood flow were investigated in chronically catheterized, nonpregnant sheep equipped with electromagnetic flow probes. PGE1 was found to be a potent dilator of the uterine vascular bed and, at initial arterial concentratios of 1.5 micron (500 ng/ml), produced peak uterine blood flows similar to those achieved by a pulsed dose of 1 microgram 17beta-estradiol; PGE2 had less active vasodilating activity. Conversely, uterine intra-arterial PGF2alpha infusions, which produced initial concentrations of 0.1 micron (50 ng/ml), promptly reduced peak estrogen-stimulated uterine blood flow by 60%. All prostaglandin infusions stimulated increases in uterine contractile frequency and base-line tone. The findings demonstrate the sensitivity of the nonpregnant sheep uterine vasculature to prostaglandins.
Segment stroke work and metabolism depend on coronary blood flow in the pig
Authors: Stowe D. F. , Mathey D. G. , Moores W. Y. , Glantz S. A. , Townsend R. M. , Kabra P. , Chatterjee K. , Parmley W. W. , Tyberg J. V.
Published: December 2017

We determined the mechanical and metabolic effects of graded myocardial ischemia in 23 open-chest, anesthetized pigs. By connecting the midportion of the left anterior descending artery (LAD) to the carotid artery via a constant volume, calibrated pump, we reduced the flow in the LAD to 0, 25, 50, and 75% of control rates for periods of 1 h. Flows of 100% and 150% were also examined. Using pairs of ultrasonic crystals to measure segment dimensions, we calculated segment shortening and thickening, and total and systolic stroke work in the ischemic and normally perfused segments. Blood gases, pH, and lactate and inosine balances were determined from the regional coronary venous blood. At coronary blood flows of 0, 25, 50, and 75% of normal resting flow, total segment work was 8 +/- 8, 25 +/- 4, 51 +/- 5, and 80 +/- 6% of control, respectively, while systolic segment work was -2 +/- 5, -10 +/- 5, 40 +/- 5, and 86 +/- 7% of control, respectively (means +/- SE). Thus, the decrease in total segment stroke work is proportional to the decrease in flow over the range 0-100%. However, no useful work (i.e., systolic work) is done until flow exceeds 25%. Segment shortening and thickening are significantly depressed with flows diminished by only 25%. Segmental inosine production correlates with lactate production and parallels decreased mechanical performance.
Reentrant excitation as a cause of cardiac arrhythmias
Authors: Wit A. L. , Cranefield P. F.
Published: December 2017

Mechanisms that cause reentry were defined in rings of tissue cut from jellyfish as early as 1906 by Mayer. The concepts were developed by Mines and Garrey during the next 10 years. Lewis then tried to demonstrate that reentry caused atrial flutter. Lewis, Garrey, and later Moe also proposed that atrial fibrillation was caused by reentry. Rosenblueth provided additional experimental evidence that reentry could cause atrial arrhythmias after crushing the intercaval bridge of atrial muscle. Recent studies by Allessie using microelectrodes have provided detailed evidence for reentry in atrial tissue. Mines in 1913 also proposed that reentry could occur in the AV node. Scherf then introduced the concept of functional longitudinal dissociation as a cause of return extrasystoles and this was later shown to happen in the node by Moe and his colleagues. Reentry can also occur between atria and ventricles utilizing accessory connecting pathways. Schmitt and Erlanger in 1913 were the first to do experiments which indicated that reentry can also occur in the ventricles. Subsequently it was shown that reentry can occur in Purkinje fiber bundles. Reentry in ventricular muscle may also cause some of the arrhythmias that occur after myocardial infarction.
Influence of low- and high-pressure baroreceptors on plasma renin activity in humans
Authors: Mark A. L. , Abboud F. M. , Fitz A. E.
Published: December 2017

We evaluated effects of the low- and high-pressure baroreceptors on plasma renin activity (immunoassay) using graded lower body suction (LBS) in six healthy men. LBS at -10 and -20 mmHg for 10 min decreased central venous pressure without changing arterial pressure and thereby presumably reduced low- but not high-pressure baroreceptor inhibition of renin release. LBS at these levels produced forearm vasoconstriction, but did not increase renin. LBS at -40 mmHg decreased central venous and arterial pulse pressure and thus reduced both low- and high-pressure baroreceptor inhibition. LBS at this level produced forearm vasoconstriction and tachycardia and increased renin from 2.1 +/- 0.4 (mean +/- SE to 7.4 +/- 1.4 ng.ml-1.h-1 (P less than 0.05). In summary, reduction in low-pressure baroreceptor inhibition in humans did not increase renin in the presence of physiological tonic inhibition from high-pressure baroreceptors. Increases in renin did not occur until there was combined reduction of high- and low-pressure baroreceptor inhibition on plasma renin activity.
Lack of specific inhibition of angiotensin II in eels by angiotensin antagonists
Authors: Nishimura H. , Norton V. M. , Bumpus F. M.
Published: December 2017

Synthetic angiotensins I and II (AI and AII) and natural eel angiotensin were injected with angiotensin antagonists into freshwater-adapted, unanesthetized American eels, Anguilla rostrata, in an attempt to characterize the vasopressor properties of angiotensins in a primitive vertebrate. A converting enzyme inhibitor, SQ 20,881, inhibited vasopressor responses to eel angiotensin (presumably AI) and [Val5,Ser9]AI, but not those to [Asn1,Val5]AII, suggesting that a converting enzyme-like substance may exist in eels. [Sar1,Thr8]AII (10 microgram/kg per min) and [Sar1,Ile8]AII (1 microgram/kg per min), which antagonize angiotensin's action in mammals, showed neither agonistic vasopressor nor antagonistic effects in eels against [Asn1,Val5]AII or eel angiotensin. [Tal8]AII ([8-thienylalanine]AII) and a higher dose of [Sar1,Ile8]AII increased eel aortic pressure themselves and reduced vasopressor responses to [Asn1,Val5]AII. This is presumably a nonspecific decrease in response during the agonistic phase of the analogs. Angiotensin receptors in the blood vessels of eels may differ from those in mammals. Alpha-adrenergic blocking drugs and reserpine partially inhibited the pressor effect of [Asn1,Val5]AII in eels.
Effect of arterial pulse pressure and hypoxia on myogenic responses in the gut
Authors: Shepherd A. P.
Published: December 2017

In intestine, raising venous pressure (PV) elicits a precapillary vasconstriction that has been ascribed to a myogenic mechanism through which passive stretch elicits active contraction of vascular smooth muscle. A previous report from this laboratory indicated that myogenic responses in the gut were largely dependent on control conditions. The purpose of the present study was to determine whether control blood flow rates or the arterial pulse pressure affects the magnitude of myogenic responses. In isolated perfused canine small bowel arterial hypoxia was used to increase blood flow. Myogenic responses to elevated PV were not significantly different in the normoxic and hypoxic periods, indicating that blood flow per se does not greatly alter myogenic responses. When gut loops were perfused with pulsatile arterial pressure, myogenic responses occurred more than twice as frequently as during nonpulsatile pefusion and they had a greater magnitude. The results are consistent with the observation that vascular smooth muscle is stimulated not only by steady stretch but also by the rate of stretch. The results also suggest that the arterial pressure pulse should be considered in the design and interpretation of future studies of local circulatory control.
Effect of uranyl ions on isometric contractions in rabbit atria
Authors: Mill J. G. , Vassallo D. V. , Campanha Vde P.
Published: December 2017

The effects of uranyl ions on isometric contractions of atrial strips of rabbit heart were studied. It was observed that uranyl ions, in a concentration of 1.1 X 10(-5) M, do not alter isometric contraction; 2.2 X 10(-5) M concentration produced a small positive inotropic effect that was magnified at a 4.5 X 10(-5) M concentration; concentrations greater than 1.8 X 10(-5) M produced a negative inotropic effect. There is evidence that the positive inotropic effect is mediated by catecholamine release, in a similar manner to the action of uranyl ions on intestinal smooth muscle preparations. This response was blocked by propranolol and also after tyramine treatment of the preparation. The negative inotropic effect seems to be mediated by a blocking effect on calcium entry through the sarcolemma during activation. Indirect evidence supporting this hypothesis was the observation of a decrease of action of uranyl ions in the presence of isoproterenol and of increased extracellular calcium concentration.
Frequency analysis of coronary intercapillary distances: site of capillary control
Authors: Feldstein M. L. , Henquell L. , Honig C. R.
Published: December 2017

Frequency distributions for minimum intercapillary distance (ICD) and functional ICD were characterized for rat heart in situ. Minimum ICD denotes spacings between adjacent capillaries whether they contain erythrocytes or not.Functional ICD is defined as spacings between contiguous capillaries perfused with erythrocytes. Minimum ICD was well fitted by both the gamma and the lognormal distributions. Functional ICD was well fitted by the lognormal, but not by the gamma, or by any mixture of the gamma with another discrete distribution. The frequency analysis is interpreted to mean that: 1) A control site distal to the true arteriole exists. This is presumably the precapillary sphincter. 21 Intercapillary anastomoses help keep the diffusion path in myocardium short and comparatively uniform. 3) Complete closure of arterioles does not occur in the unstressed heart. 4) Blood flow and conditions for diffusion can be controlled independently.
Choline acetyltransferase activity in rat heart after transplantation
Authors: Lund D. D. , Schmid P. G. , Kelley S. E. , Corry R. J. , Roskoski R.
Published: December 2017

Choline acetyltransferase (CAT) catalyzes the biosynthesis of acetylcholine according to the chemical equation: Acetyl-CoA + Choline in equilibrium Acetylcholine + CoA. To demonstrate the neuronal relationship of this enzyme, CAT activity was measured in hearts to which the extrinsic innervation was completely interrupted by extirpation of the heart from a donor animal and transplantation in a heterotopic position into the recipient's abdominal cavity. After the animals were killed at 8 days, enzyme activity in the transplanted hearts was measured and compared with that of the recipient. Choline acetyltransferase activity decreased 98% in the right atrium of the transplanted denervated hearts, 94% in the SA node, 87% in the left atrium, 80% in the right ventricle, and about 50% in the interventricular septum and left ventricle. These data show that sectioning the extrinsic parasympathetic innervation to the heart results in variable decreases in CAT activity, a finding which confirms that CAT activity is related to the extrinsic cholinergic innervation. The extrinsic (preganglionic) component of the parasympathetic system is nonuniform and supplies predominantly the specialized regions of the heart with conduction tissue. The residual enzyme activity is related to intrinsic (postganglionic) parasympathetic neurons. The intrinsic component is uniformly distributed to both specialized and contractile regions of the heart.
Actions of prostaglandins on isolated perfused cat coronary arteries
Authors: Ogletree M. L. , Smith J. B. , Lefer A. M.
Published: December 2017

Effects of prostaglandins on coronary arterial smooth muscle were studied in isolated perfused cat coronary arteries. This preparation was shown to be responsive to known vasoactive agents, including angiotensin II, adenosine, and norepinephrine. Prostaglandins E2 and F2 alpha (PGE2 and PGF2 alpha) produced dose-dependent coronary arterial constriction at concentrations of 3 times 10(–9) M or greater. PGE1 produced a biphasic dose-response curve with constriction at low concentrations greater than 10(–7) M.PGI2 dilated coronary arteries at concentrations greater than 10(–8) M. Inhibition of endogenous prostaglandin synthesis with meclofenamate potentiated responses to prostaglandins. The endoperoxide, PGH2, slightly constricted cat coronary arteries. However, in the presence of human platelet microsomes, PGH2 was converted to thromboxane A2(TxA2), which was the most potent coronary artery constrictor among the naturally occurring compounds studied. Analysis of coronary artery perfusate for TxB2 confirmed the thromboxane generation, which was markedly lower in the presence of imidazole. Two synthetic endoperoxide analogs produced potent coronary arterial constriction. Induction of hypoxia to a PO2 of 50 mmHg or increasing basal tome with 30 mM KCl did not diminish coronary artery response to prostaglandins, suggesting that prostaglandins released from ischemic myocardial tissue may influence coronary arterial tone.
The structure and function of the myocardial cell surface
Authors: Langer G. A.
Published: December 2017

External to the lipid bilayer or unit membrane at the surface of the myocardial cell is the glycocalyx. This coat is approximately 50 nm thick and is composed for two layers, the surface coat (SC) and the external lamina (EL). The SC is an integral part of the sarcolemma and many of its glycoproteins penetrate into or through the lipid bilayer. The glycocalyx invaginates with the unit membrane to fill the transverse tubules of the cell. Both layers contain abundant fixed negatively charged sites and a prominent constitutent of both is sialic acid. Removal of sialic acid produces a large specific increase in sarcolemmal calcium permeability without perturbation of potassium permeability. Sialic acid also accounts for a component of negatively charged sites which, with other acidic mucopolysaccharides, contributes to cationic binding at the surface of the cell. Calcium bound at the surface seems to be of importance in the excitation-contraction (EC) coupling sequence whether as a source of "trigger" calcium for the sarcotubular system or as a direct activator of the myofilaments. The bound Ca appears to be in rapid equilibrium with Ca in the vascular and interstitial spaces and is the probable immediate source of the Ca that crosses the sarcolemma. The integrity of the glycocalyx appears to be necessary in the prevention of uncontrolled entry of Ca into the cell.
Reflex responses of abdominal vascular capacitance from aortic baroreceptors in dogs
Authors: Karim F. , Hainsworth R. , Pandey R. P.
Published: December 2017

The vascularly isolated abdominal circulation of chloralose-anesthetized dogs was perfused at constant flow through the aorta and drained at constant pressure from the inferior vena cava. Changes in resistance were calculated from changes in perfusion pressure and changes in capacitance were calculated by integrating changes in venous outflow. While carotid sinus pressure was constant, a decrease in pressure in the vascularly isolated aortic arch, over the whole range of baroreceptor sensitivity, decreased abdominal vascular capacitance by 2.9 ml-kg-1 (mean, SE +/- 0.42) and increased the abdominal vascular resistance by 35 +/- 7.1%. Decreases in pressure in the vascularly isolated carotid sinuses, while aortic pressure was constant, decreased capacitance by 5.0 +/- 0.62 ml-kg-1 and increased resistance by 72 +/- 15.9%. Responses of capacitance and resistance to changes in aortic pressure were greatest when carotid pressure was held near threshold levels and least when it was held at levels that would maximally excite carotid baroreceptors. The responses to changes in aortic pressure were abolished when the venous nerves were cooled or the splanchnic nerves were cut.
Dissociation of energetic state and potassium loss from anoxic myocardium
Authors: Rau E. E. , Langer G. A.
Published: December 2017

Cellular high-energy phosphate levels and 42K exchange were studied in isolated, interventricular rabbit septa at 28 degrees C. Septa were perfused with a modified Tyrode solution that contained glucose as the metabolic substrate. Anoxia was induced by switching to solution equilibrated with N2-CO2 gas. Potassium lost during anoxia by increased efflux from the cells was measured by 42K. Whole tissue levels of ATP, ADP, phosphocreatine, and total creatine were determined. The effects of 20-min anoxic stresses were evaluated in each of four groups of septa: 1) control (perfused with regular solution and paced at 42 excitations/min; 2) E-C uncoupled (by perfusing with solution containing 50 micron Ca2+); 3) quiescent (spontaneous contraction rate less than 1/min); and 4) perfused with high glucose solution (20 mM). Compared to the control group, only quiescence significantly decreased the potassium loss during anoxia; the cellular energetic state was well maintained during stress by both E-C uncoupling and quiescence. The results indicate that the increase in potassium efflux during brief anoxic stress is largely excitation dependent and can be dissociated from contraction and cellular energetic state.
Pulmonary capillary pressure in intact dog lungs
Authors: Gabel J. C. , Drake R. E.
Published: December 2017

We used a gravimetric method to determine the ratio (gamma) of pulmonary venous to total pulmonary vascular resistance in intact dog lungs. From this ratio, pulmonary capillary pressure (Pc) can be calculated. The average value of gamma was 0.50 +/- 0.06 (mean +/- SD) in 10 dogs. We found no correlation between gamma and PO2, PCO2, pH, or hematocrit in the narrow ranges of these experiments. Over the capillary pressure range of 22.4--35.2 mmHg we found no correlation between gamma and Pc. The value of gamma found in this study is not significantly different from the value found in isolated perfused lungs.
Determinations of blood flow and shunting of 9- and 15-micrometer spheres in regional beds
Authors: Fan F. C. , Schuessler G. B. , Chen R. Y. , Chien S.
Published: December 2017

In 17 pentobarbitalized dogs, the shunting of 15-micrometer and 9-micrometer microspheres was studied in the brain, myocardium, kidney, intestine, and lung. The veins of these organs were catheterized for constant blood withdrawal for 2 min by direct venipuncture. The ratio of microsphere radioactivity in the venous blood to that in the arterial blood gave the shunting of microspheres by the venous sampling technique. The 15-micrometer microspheres showed 2% or less shunting for all organs studied, whereas the 9-micrometer microspheres had shunting ranging from 3% in the coronary sinus to 24% in the portal vein. The shunting of 9-micrometer microspheres was also calculated from direct tissue counting, where the 15-micrometer spheres were considered to be completely entrapped. The results of direct tissue counting indicate that the 2-min venous sampling underestimates microsphere shunting. CO2 administration increased significantly the shunting of 9-micrometer spheres, whereas the shunting of 15-micrometer spheres determined by venous sampling remained less than 2%. Consideration of shunting indicates that the 15-micrometer microspheres might be more appropriate for regional organ blood flow measurements, including the myocardium.
Microvascular myogenic reaction in the wing of the intact unanesthetized bat
Authors: Bouskela E. , Wiederhielm C. A.
Published: December 2017

Microvascular dimension and flow responses to stepwise changes in arterial and venous pressures, ranging from zero to +100 mmHg and zero to -75 mmHg have been recorded. Observations were made in arterioles, terminal arterioles, and precapillary sphincters in the wing web of intact, unanesthetized bats. The results show for all categories of vessels that with reduced transmural pressures there is a progressive increase in mean diameter and a decrease in rhythmic vasomotion rate. Flow changes are variable. For elevated transmural pressures there is a vasoconstriction with drastic flow reduction that is inconsistent with metabolic control. However, after prolonged elevation of pressure there is a progressive increase in flow, suggesting a "metabolic escape". Computed wall tension remains reasonably constant for a wide range of transmural pressures, suggesting that wall tension may be the controlled variable. These findings support the hypothesis of a myogenic reaction as a mechanism for maintenance of basal vascular tone in the intact unanesthetized bat.
Species differences in cardiac energetics
Authors: Loiselle D. S. , Gibbs C. L.
Published: December 2017

The energy flux of rat, guinea pig, and cat papillary muscles was measured myothermically under resting, isometric, and isotonic conditions at 27 degrees C. Resting heat rate was highest in the smallest species and declined with body size. The slope of the isometric heat-stress relationship was constant across species, whereas the stress-independent heat component was least for rat muscles. The shape of the load enthalpy relationship was similar across species. Maximum mechanical efficiency, work-enthalpy, occurred with lighter loads than for skeletal muscle (approximately 0.2 Po). Rat muscle had the smallest enthalpy per beat and the highest active mechanical efficiency, but this advantage was nullified by the higher basal heat rate. The myothermic data are compared with cardiac oxygen consumption values in the literature and it is concluded, contrary to the deductions of common dimensional arguments, that cardiac energy expenditure across species is not directly proportional to heart rate. Reasons for this discrepancy are considered together with the likely contribution of cardiac metabolism (EH) to total body metabolism (EB). It seems likely that smaller species have lower EH/EB.
Coronary dynamics and myocardial metabolism in the diabetic newborn lamb
Authors: Lee J. C. , Downing S. E.
Published: December 2017

Diabetes mellitus (DM) was produced in 17 neonatal lambs by a single intravenous injection of alloxan monohydrate (150 mg/kg). All developed hyperglycemia (greater than 300 mg/100 ml) and glycosuria after 24 h, but none exhibited ketonuria or acidosis. Plasma insulin levels were reduced to about 20% of those appropriate for the plasma glucose levels. Glucose tolerance tests (intravenous) were also consistent with reduced insulin reserve. Measurements of left ventricular performance were obtained under constant hemodynamic conditions in 16 diabetics and did not differ from those in 10 normal lambs. However, myocardial uptake of glucose was sharply reduced and fatty acid uptake was less. Myocardial O2 consumption (MVO2) was unchanged. Coronary flow (CF) was significantly lower in the diabetics (P less than 0.001). Pressure-flow studies were also done and demonstrated a consistent reduction in CF at a given aortic pressure in DM compared with controls. These findings indicate that coronary vascular resistance is elevated in the lamb with DM, and this is not explained by a change in MVO2. Oxygen requirements of the diabetic hearts were satisfied by increased extraction.
Comparison of arterial wall mechanics in normotensive and spontaneously hypertensive rats
Authors: Cox R. H.
Published: December 2017

Segments of carotid artery from Wistar (NW), Kyoto Wistar (WKY), and spontaneously hypertensive rats (SHR) were used to compare mechanical properties and connective tissue composition. Pressure-diameter measurements were made under conditions of active (5 microgram/ml norepinephrine) and passive (0 mM Ca2+ and 2 mM EGTA) smooth muscle. Systolic blood pressures averaged NW, 121 +/- 3; WKY, 124 +/- 4; and SHR, 187 +/- 5 MMHg. Passive mechanics were stiffest in SHR and most compliant in NW arteries. No differences in collagen-elastin ratio were found but collagen + elastin was lowest in SHR and highest in NW carotids. These results are not consistent with current concepts of the contribution of connective tissue elements to passive mechanics. Maximum stress development was NW, 561 +/- 49; WKY, 735 +/- 50; and SHR, 944 +/- 79 X 10(3) dyn/cm2. Diameter reductions to NE at 100 mmHg were NW, 17.6 +/- 2.4%; WKY, 16.7 +/- 2.0%; and SHR, 24.8 +/- 2.4%. The former suggests different contractile protein contents or more efficient intercellular force coupling in SHR. The latter suggests a more effective contractile apparatus as a result of stiffer passive muscle elements and/or a relatively larger wall thickness.
Participation of slow inward current in the Purkinje fiber action potential overshoot
Authors: Mary-Rabine L. , Hoffman B. F. , Rosen M. R.
Published: December 2017

We used microelectrode techniques to study the relationship of canine Purkinje fiber membrane potential and the action potential (AP) overshoot. At the maximum diastolic potential, -93.0 +/- 0.5 (SE) mV, AP overshoot was +37.7 +/- 0.4 mV. There was a range of membrane potentials (MP) less negative than the maximum diastolic potential from which action potentials were elicited with an overshoot greater than the control. Starting at an MP of less than -78.7 +/- 0.4 mV, AP overshoot was less than control. A maximum overshoot of +40.2 +/- 0.4 mV occurred at an MP of -85.4 +/- 0.4 mV. The relationship of the maximum upstroke velocity (Vmax) of phase 0 depolarization to MP was sigmoidal. Peak Vmax, 497 +/- 13 V/s, occurred at MP greater than or equal to -89.3 +/- 0.5 mV. The increase in overshoot was enhanced as perfusate [Ca2+] increased and decreased as [Ca2+] decreased. Slow-channel blocking agents and tetrodotoxin (TTX) depressed the peak of the curve relating overshoot to MP. TTX also decreased Vmax. The effect of TTX on overshoot but not on Vmax was reversed with Ca2+, 8.1 mM. The increase in overshoot for action potentials initiated during the terminal part of phase 3 was due to a slow, delayed component of the upstroke and appears to result from the slow inward current.
Presynaptic inhibition of canine renal adrenergic nerves by acetylcholine in vivo
Authors: Robie N. W.
Published: December 2017

Experiments were performed in anesthetized dogs to determine whether previously reported in vitro inhibition of sympathetic neurotransmitter release by acetylcholine could be demonstrated in the renal vasculature of the intact animal. Vasoconstrictor responses to renal sympathetic nerve stimulation at varying frequencies were compared to intra-arterial injections of norepinephrine before and during intra-arterial infusions of acetylcholine, 2.5--80 micrograms/min. The vasoconstrictor responses to nerve stimulation were inhibited to a greater extent than were responses to norepinephrine during infusions of acetylcholine. The inhibitory effects of acetylcholine on nerve stimulation were dose and frequency dependent. The inhibition was blocked by atropine but not altered by physostigmine. Changes in renal blood flow per se did not contribute to the inhibitory effect of acetylcholine, since another vasodilator agent, sodium acetate, did not affect the nerve stimulation-norepinephrine vasocontriction relationship. Thus, acetylcholine produced inhibition of in vivo renal sympathetic vasoconstrictor responses, and the receptor involved appears to be muscarinic.
Interaction of thrombin with mammalian platelets
Authors: Sidhu P. , Sutherland S. B. , Ganguly P.
Published: December 2017

In this study we have explored the interaction of thrombin with platelets from human and rat. Compared to human platelets, rat platelets suspended in plasma required a higher concentration of thrombin for aggregation. This difference in sensitivity to thrombin was maintained when platelets were washed and suspended in buffer. Platelets from both mammals bound thrombin and showed a similar number of binding sites. However, the apparent dissociation constant of thrombin binding for rat platelets was approximately 15-fold higher than that for human. Thus, the decreased aggregation response of rat platelets may be due to a reduced binding of thrombin to its receptor. It is known that the thrombin receptor is located on the platelet surface. Gel electrophoresis of platelets followed by specific staining as well as fluorography showed significant differences in the surface glycoproteins of human and rat platelets. Human platelets showed labeled components corresponding to 210,000 and 160,000 daltons, whereas rat platelets showed glycoproteins with molecular weights of 240,000 and 190,000. A 135,000-dalton component was present in platelets from both sources. These results suggest that either or both glycoproteins of 210,000 and 160,000 daltons may be involved in the interaction of thrombin with human platelets.
Vascular responses in canine subcutaneous adipose tissue to hypothalamic stimulation
Authors: Parker R. E. , Hall R. E. , Marr H. B. , Skinner N. S.
Published: December 2017

The present studies investigated vascular responses to electrical stimulation of the posterior hypothalamus in isolated but perfused and innervated subcutaneous adipose tissue in adult dogs. Three groups of dogs were distinguished: in one, electrical stimulation elicited vasodilation; in another, vasoconstriction, and in a third, neither significant vasodilation nor vasoconstriction occurred. Histological examination revealed that electrode placements were in the medial posterior hypothalamus, the lateral posterior hypothalamus, and the medial septal region, respectively. Hypothalamic stimulation failed to alter concentrations of free fatty acids or glycerol in venous blood from subcutaneous fat. Local beta-adrenergic block (propranolol) reversed the vasodilation to vasoconstriction while local alpha-adrenergic block (dihydroergotamine) abolished the vaso constrictor response. These results suggest that selective stimulation of the posterior hypothalamus results in neurogenic activation of both alpha- and beta-adrenergic mechanisms in adipose tissue vasculature. beta-Adrenergic vasodilation appears to predominate if the electrode is located medially, and alpha-adrenergic vasoconstriction appears to predominate if the electrode is located in the lateral posterior hypothalamus.
A method of intrarenal blood flow measurement using xenon-133 in the intact rat
Authors: Butt T. J. , Bolli P. , Jones D. R. , Wallis A. T. , Simpson F. O.
Published: December 2017

A method is described for measuring distribution of intrarenal blood flow in anesthetized rats by a xenon-133 washout technique that avoids the trauma of opening the abdominal cavity and manipulating the kidney. Precise delivery of the tracer to the kidney and fine collimation of the radiation reduces the amount of tracer required. Washout curve analysis is achieved by a multifit computer program that accepts only count rates and time as input data.
Indirect blood pressure determination by Doppler technique in renal hypertensive cats
Authors: Klevans L. R. , Hirkaler G. , Kovacs J. L.
Published: December 2017

The Doppler ultrasonic recording technique was used to measure systolic and diastolic blood pressures indirectly in renal hypertensive cats. The accuracy of the method was evaluated by comparing indirect blood pressures from one leg of a cat with direct pressure measurements from the other leg. A linear relationship existed between indirect and direct systolic and diastolic pressures. The consistency of the method was assessed by measuring blood pressure during a 5-h monitoring period in normotensive and renal hypertensive cats. No significant variation occurred over this period. The sensitivity of the method to blood pressure changes was determined also. A significant reduction in systolic and diastolic pressure induced by hydralazine, 10 mg/kg po, was recorded during a 5-h monitoring period. The development of renovascular hypertension was followed for approximately 70 days. Systolic pressure rose in a logarithmic fashion from 160 to a maximum of 240 mmHg. It was concluded that the Doppler ultrasonic technique is a simple and reliable method for recording indirect blood pressure acutely and chronically in conscious unrestrained cats.
Postnatal changes in response of canine neonatal pulmonary arteries to histamine
Authors: Newman John H. , Souhrada Joseph F. , Reeves John T. , Arroyave Carlos M. , Grover Robert F.
Published: December 2017

Page H76: John H. Newman, Joseph F. Souhrada, John T. Reeves, Carlos M. Arroyave, and Robert F. Grover. “Postnatal changes in response of canine neonatal pulmonary arteries to histamine.” Page H79: the legend presently listed with Fig. 5 belongs to Fig. 6. Page H80: the legend presently listed with Fig. 6 belongs to Fig. 7, and the legend presently listed with Fig. 7 belongs to Fig. 5.
Helically cut vascular strip preparation: geometrical considerations
Authors: Herlihy J. T.
Published: December 2017

The present study examines certain constraints associated with the use of helically cut strips obtained from the rat aorta. The angle (phi) at which a strip is cut from a vessel segment is intimately related to the strip width as well as the vessel circumference. Quantitatively, the relationship can be expressed by the equation cos phi = strip width/vessel circumference. To obtain strips of equal width from vessels of different diameters, the angle (phi) at which the strips are cut must differ. The stress developed by vascular strips was found to be a function of phi. Strips cut transverse to the long axis developed approximately 20 times more stress than strips cut parallel to the long axis. Strips cut at other angles developed intermediate stresses. This study demonstrates that helically cut strips lend themselves to artifact with respect to the tension-generating capacity of vascular smooth muscle if the geometrical considerations of strip width, vessel diameter, and the pitch of the helix are ignored.
Capillary recruitment in exercise: rate, extent, uniformity, and relation to blood flow
Authors: Honig C. R. , Odoroff C. L. , Frierson J. L.
Published: December 2017

Erythrocyte-containing capillaries were counted in dog gracilis muscles freeze-clamped at rest and after twitch contraction at 4/s. In each of 21 muscles, 6--8 blocks were examined at -70 degrees C without fixation or staining; 15 fields were counted per block. Frequency analysis of capillaries per field based on the negative binomial distribution indicated that capillary density at rest was controlled by arterioles. Active vasomotion of these arterioles was "switched off" within 5 s after onset of exercise. Capillary density was then determined passively by stochastic rheologic factors acting at the individual capillaries. Thus exercise changes the site and the mechanism of capillary control. Recruitment occurred first where capillary density was lowest, and was complete in 15 s; this greatly decreased the heterogeneity of capillary spacing. Mean capillary density increased 1.5- to 3-fold, whereas flow increased almost 7-fold. Calculated mean velocity and mean transit time of erythrocytes in capillaries were 1.1 mm/s and 920 ms at rest and 4.2 mm/s and 215 ms after 3 min of exercise.
Analysis of sympathetic discharges during cardiogenic hypertensive chemoreflex
Authors: Hageman G. R. , Urthaler F. , Swatzell R. H. , James T. N.
Published: December 2017

Serotonin activates a cardiogenic hypertensive chemoreflex. During this reflex, sympathetic efferent neural discharges were examined in 10 anesthetized dogs. Thoracic nerves were identified, severed distally, and placed across electrodes. The efferent neurogram was recorded along with an electrocardiogram and blood pressure and stored on tape. Neurograms were later analyzed by a Lab 8/e computer with a Schmitt trigger. The resting tone and the elicited discharges of the multifiber preparations were plotted as poststimulus histograms. The integrals of the histograms were normalized. During the reflex, sympathetic efferent discharges averaged 4.9 (+/- 0.8) s in duration and the total discharge frequency was 199 (+/- 16)% of control tone. The evoked peak blood pressure response averaged 221/171 mmHg. Following autonomic blockade, the attenuated blood pressure response averaged 125/96 mmHg. The sympathetic efferent discharges then lasted 5.2 (+/- 0.7) s (NS). However, total discharge frequency (268 +/- 37% of control tone) was significantly greater (P less than 0.01) that before autonomic blockade. These data suggest that baroreceptors influence the rate of discharge and the total amount of neural traffic, but not the duration of the sympathetic response evoked by the cardiogenic hypertensive chemoreflex.
Responses to prostaglandins H2 and I2 of isolated dog cerebral and peripheral arteries
Authors: Toda N.
Published: December 2017

In helical strips of cerebral and peripheral arteries isolated from dogs and contracted with prostaglandin F2 alpha (PGF2 alpha), PGH2 produced a slight transient contraction followed by a relaxation. The relaxation was greater and persisted longer in mesenteric and renal than in cerebral and coronary arteries. Following tranylcypromine or 15-hydroperoxy arachidonic acid, both PGI2 synthetase inhibitors, the relaxation was reversed to a contraction. The contraction was abolished by polyphloretin phosphate, a prostaglandin antagonist. Concentrations of PGI2Na sufficient to produce the same magnitude of relaxations as those induced by PGH2 were greater in mesenteric arteries. PGI2Na or PGI2 methylester caused a dose-related relaxation of the strips contracted with PGF2 alpha or K+, the relaxation being in the order: mesenteric greater than renal greater than coronary greater than cerebral. 6-Keto PGF1 alpha relaxed only mesenteric arteries. It may be concluded that PGH2 is rapidly converted to PGI2 and causes a marked relaxation in dog cerebral and peripheral arteries, the conversion being greater in mesenteric arteries. PGH2, PGE2, and PGF2 alpha all appear to share the same site of excitatory action on arterial smooth muscles. Responses of a variety of isolated dog arteries to vasodilating prostaglandins apparently differ.
Intestinal tissue PO2 and microvascular responses during glucose exposure
Authors: Bohlen H. G.
Published: December 2017

The microvessels responsible for the major decrease in intestinal vascular resistance during the presence of glucose were defined. In addition, the normal distribution of tissue PO2 in the various layers of the intestinal tissue was measured at rest and during glucose exposure to determine if part of the absorptive hyperemia mechanism is related to a decrease in tissue PO2. In the rat small intestine, exposure of the mucosa only to glucose concentrations of 25--500 mg/100 causes a 20--25% dilation of all submucosal vessels in series with the mucosal vessels and mucosal arterioles. Total intestinal blood flow increased to 200-210% of control at all glucose concentrations. The tissue and perivascular PO2 in the villus apex decreased from 14.8 +/- 1.2 (SE) mmHg at rest to 6--8 mmHg during glucose exposure; the PO2 in the muscle and submucosal layers tended to slightly increase above a normal of 26.4 +/- 1.6 mmHg during glucose exposure. The data indicate virtually all intestinal arterioles are equally involved in absorptive hyperemia. The dilation of mucosal vessels may be related to a decrease in tissue PO2, but submucosal vessels dilate even though PO2 is slightly increased.
Reduced coronary collateral resistances after chronic ventricular sympathectomy
Authors: Jones C. E. , Scheel K. W.
Published: December 2017

Previous work has suggested that chronic ventricular sympathectomy causes a reduction in coronary collateral resistances. In the present experiments an isolated dog heart procedure was used to directly measure directional collateral resistances in 12 acutely denervated controls and 8 hearts that had undergone ventricular sympathectomy 2 wk earlier. In the procedure, the major coronary arteries were perfused separately but simultaneously during maximum vasodilation, and collateral resistances supplying the vascular beds of the arteries were determined by the double retrograde flow method. In the sympathectomized hearts, all collateral resistances were 47--65% less than in the controls (P less than 0.05). Also, in all hearts, minimum antegrade coronary resistances were determined from pressure-flow relationships in the major coronary arteries. Minimum coronary resistances in the 2 groups were not significantly different (P greater than 0.05). These results indicate that 2 wk of ventricular sympathectomy indeed causes a reduction in coronary collateral resistances, but has no effect on coronary resistances.
Vascular reactivity to angiotensin II in the normotensive and hypertensive pregnant ewe
Authors: Lieb S. M. , Cabalum T. , Zugaib M. , Erkkola R. , Tabsh K. , Ushioda E. , Nuwayhid B. S. , Brinkman C. R. , Assali N. S.
Published: December 2017

The circulatory responses to progressively increasing doses of angiotensin II were studied in the same group of chronically instrumented unanesthetized pregnant sheep during three consecutive periods: a) normotensive with intact kidneys; b) normotensive with unilateral nephrectomy; and c) one-kidney hypertension. The results show that 1) the pressor response to a given dose of angiotensin was significantly greater in the normotensive than in the hypertensive condition; 2) uterine blood flow decreased markedly with the development of hypertension; 3) uterine circulatory response to angiotensin depended on the dosage; the response was less the the hypertensive than in the normotensive condition; 4) renal blood flow decreased and renal vascular resistance increased during angiotensin infusion, but the response was less in the hypertensive than in the normotensive condition; the response of the renal circulation decreased with increasing doses of angiotensin. These observations suggest a generalized vascular refractoriness to exogenous angiotensin II in the pregnant ewe with experimental renal hypertension.
alpha-Stimulation protects exercise increment in skeletal muscle oxygen consumption
Authors: Nellis S. H. , Flaim S. F. , McCauley K. M. , Zelis R.
Published: December 2017

Oxygen consumption (VO2) in an isolated, autoperfused, statically exercising canine gracilis muscle (2.5% P0) was studied in low blood flow (Q) states induced by constant norepinephrine (NE) infusion and by mechanical occlusion (MO). Q and VO2 were evaluated at rest (Qc and VO2c), after 5 min of exercise (Qe and VO2e) and after 5 more min of exercise with either NE or MO (Qt and VO2t). Data were normalized and plotted as the VO2e-VO2t)/(VO2c-VO2e) vs. (Qe-Qt)/(Qc-Qe) and equations of the lines for NE (y = 0.090x + 0.048) and for MO (y = 0.488x + 0.070) were determined. The slopes of the lines, tested by analysis of covariance, were significantly different (P less than 0.005). These data indicate that when NE reduced Q during exercise, the exercise induced in VO2 was protected to a greater degree than when MO reduced Q under similar conditions. To determine if the effect of NE on VO2 was secondary to a beta-adrenergic-receptor-mediated of skeletal muscle metabolic processes, the experiments were repeated in the presence of beta-blockade with propranolol. In the presence of beta-blockade, the effects of NE on skeletal muscle VO2 were unchanged. It is therefore hypothesized that the mechanism of this effect of NE may be an increase in the efficiency of oxygen extraction resulting from a redistribution of blood flow to more active muscle fiber regions.
Role of the papillary muscle in opening and closure of the mitral valve
Authors: Marzilli M. , Sabbah H. N. , Lee T. , Stein P. D.
Published: December 2017

Dimensional changes of the left ventricular anterolateral papillary muscle of six open-chest dogs were measured continuously throughout the cardiac cycle in order to evaluate the role of the papillary muscle in opening and closing of the mitral valve. Dimensional changes were measured with ultrasonic dimension gauges. Maximal shortening and maximal elongation of the papillary muscle followed maximal shortening and elongation of a segment of the free wall of the left ventricle by 65 +/- 6 (SE) ms. Maximal elongation of the papillary muscle occurred 25 +/- 2 ms after the onset of ejection. Maximal shortening of the papillary muscle occurred 68 +/- 5 ms after the aortic incisura and 10 +/- 2 ms after the crossover of left ventricular and left atrial pressure. The papillary muscle shortened 14 +/- 4%. The percentage of papillary muscle shortening that occurred after the aortic incisura was 39 +/- 7%, and the percentage of shortening that occurred after the crossover of left ventricular and left atrial pressure was 3 +/- 1%. The observed shortening of the papillary muscle throughout left ventricular isovolumic relaxation suggests that the papillary muscle may have a role in opening the mitral valve. Conversely, elongation of the papillary muscle in the late portion of diastole appears necessary to permit proper closure of the mitral valve leaflets.
Effect of acute volume loading on aortic smooth muscle activity in intact dogs
Authors: Dujardin J. P. , Paul L. T. , Pieper H. P.
Published: December 2017

Experiments were performed to study the aortic smooth muscle responses to acute volume loading with dextran 70. To analyze the aortic smooth muscle activity, diastolic aortic pressure was plotted vs. aortic internal diameter to obtain a pressure-diameter relationship (PDR) curve. Aortic pressure and diameter were measured by means of a catheter-tip instrument. To obtain the relationships over a large range of pressure and diameter, slow oscillations (period, 4-5 s) in aortic pressure were induced by means of an external pump. In 15 anesthetized dogs, the blood volume was expanded by 33.6 +/- 0.6% (SE) of the control volume. After this volume expansion, aortic diameter for a given pressure was increased by 6.0 +/- 1.0% of the control value. The slope of the PDR curve for a given pressure was decreased by 16.1 +/- 3.9%, and the compliance per centimeter was increased by 30.2 +/- 5.9%. All these changes were significant at P less than 0.001. It was also shown that these responses were not related to the changes in mean arterial pressure and were not mediated by reflexes through the carotid sinus and vagus nerves.
Methods to quantify silver in autoradiographs
Authors: Fry D. L. , Tousimis A. J. , Talbot T. L. , Lewis S. J.
Published: December 2017

The developed silver in specially prepared photographic films (PF) and autoradiographs (AR) of radiolabeled arterial tissue was quantified by direct grain counting (GC), microdensitometry (OD), and by electron probe X-ray microanalysis (EPA). The EPA data was proportional to the OD data with a very small variance. The GC data increased with the EPA data, but showed a large variance. The EPA signal was shown 1) to be reproducible even after multiple traverses across the specimen, 2) to be directly proportional to the electron beam current and emulsion silver concentration, and 3) to be insensitive to a) beam size, b) current density, c) energy above 17 keV, or d) nonuniformities in the thickness of the conductive coating on the specimen.