bluuebunny/crossref_metadata_2025 huggingface dataset:
Metabolism of sulfoconjugated thyroid hormone derivatives in developing sheep
Authors: Polk D. H. , Reviczky A. , Wu S. Y. , Huang W. S. , Fisher D. A.
Published: December 2017

Although the production of thyroxine (T4) in the developing ovine fetus ranges from 20 to 50 micrograms.kg-1.day-1, production rates for 3,5,3'-triiodothyronine (T3) average only 1-2 micrograms.kg-1.day-1, whereas reverse T3 (rT3) production rates approach 5-6 micrograms.kg-1.day-1. Thus the fate of the majority of fetal T4 production is uncertain. Recently we have reported significant concentrations of various thyroid hormone sulfoconjugates in serum and other fetal compartments. In the present study, we used steady-state kinetic techniques in developing sheep to establish the clearance and production rates for T4, T3, and rT3 sulfates. These studies confirm that T4, T3, and rT3 sulfate are predominant metabolites of thyroid hormone in the developing ovine fetus. Plasma clearance rates for T3, T4, and rT3 sulfates are low in the fetus, averaging 0.67 +/- 0.07, 1.46 +/- 0.11, and 4.1 +/- 1 ml.kg-1.min-1, respectively. Clearance rates for these thyrosulfoconjugates increase two to fourfold postnatally, probably reflecting increased activity of 5'-monodeiodinase after birth. Moreover, fetal production rates for these sulfated thyroid hormone metabolites exceed those of 2-wk-old sheep 4- to 10-fold. The data suggest that a significant route of fetal T4 metabolism is sulfation followed by deiodination to rT3 sulfate.
Mineralocorticoid antagonist inhibits stress-induced blood pressure response after repeated daily warming
Authors: Van den Berg D. T. , de Jong W. , de Kloet E. R.
Published: December 2017

We report here that with a direct method for measurement of cardiovascular parameters in conscious rats, intracerebroventricular administration of the mineralocorticoid receptor (MR) antagonist RU-28318 (100 ng) reduces the blood pressure, heart rate, and the corticosterone response to a brief restraint stress, provided the rats were previously subjected to a daily 30-min exposure to 32 degrees C for 2 wk. The daily exposure to warming and restraint stress are applied identically to the training procedure required for indirect blood pressure measurement using the tail-cuff method. The basal arterial pressure is not affected by the MR antagonist. The effect of the MR antagonist on the stress-induced pressor response develops with a delay of several hours in the normotensive rats. The corticosterone response to daily warming and stress is also attenuated by the intracerebroventricular infusion of MR antagonist but with shorter onset and shorter duration. The findings suggest that conditioning to daily warming and stress imposes mineralocorticoid dependency of the pressor response, which involves MR functioning in brain.
Effects of neuropeptides on heart rate in dogs: comparison of VIP, PHI, NPY, CGRP, and NT
Authors: Rigel D. F.
Published: December 2017

This study was designed to evaluate the potential chronotropic actions of several cardiac neuropeptides in pentobarbital-anesthetized dogs. After bilateral vagotomy and stellectomy and muscarinic receptor blockade, I injected vasoactive intestinal polypeptide, peptide histidine isoleucine, neuropeptide Y, neurotensin, and calcitonin gene-related peptide into the intact sinus node artery. Neurotensin, calcitonin gene-related peptide, and neuropeptide Y exhibited no physiologically significant changes in heart rate. However, the structural homologues vasoactive intestinal polypeptide and peptide histidine isoleucine each augmented heart rate with maximal increases (approximately 120 beats/min) similar to those of norepinephrine. Vasoactive intestinal polypeptide and peptide histidine isoleucine were twice and 1/18, respectively, as potent as norepinephrine. The cardioacceleratory responses to vasoactive intestinal polypeptide and peptide histidine isoleucine were more slowly developing and longer lasting than those of norepinephrine. The responses to these two peptides were unchanged after beta-adrenergic blockade with propranolol in a dose sufficient to eliminate or greatly attenuate the norepinephrine tachycardia. These results indicate a potential role of endogenous vasoactive intestinal polypeptide and peptide histidine isoleucine in nonadrenergic, noncholinergic heart rate control in the dog.
Inotropic responses change during postnatal maturation in rabbit
Authors: Artman M. , Kithas P. A. , Wike J. S. , Strada S. J.
Published: December 2017

Inotropic response to four different types of pharmacological stimuli were compared in isolated right ventricular papillary muscles from newborn (24–48 h of age), immature (14–16 days), and adult (6–7 mo) rabbits. Forskolin, a direct activator of adenylate cyclase, produced a 12.5-fold increase in the maximal rate of tension development in the newborn group. The maximum response to isoproterenol was only 45% of the maximum forskolin response, suggesting incomplete physiological coupling of myocardial beta-adrenergic receptors to adenylate cyclase at birth. In contrast to the substantial inotropic response to agents that stimulate adenosine 3',5'-cyclic monophosphate (cAMP) generation (forskolin and isoproterenol), a selective inhibitor of cAMP hydrolysis (milrinone) was relatively ineffective in the newborn group. Sulmazole, a drug that enhances calcium sensitivity of the contractile proteins, produced its greatest inotropic effect in immature myocardium. Cytosolic high-affinity cAMP phosphodiesterase activity was partially purified from ventricular homogenates by anion-exchange chromatography. The kinetics of cAMP hydrolysis (Km and Vmax) and inhibitory potency of milrinone were comparable in each age group. Thus the age-related differences in inotropic responsiveness may not be attributable to postnatal changes in myocardial cytosolic high-affinity cAMP phosphodiesterase activity.
Properties and subcellular localization of myocardial fatty acyl-coenzyme A oxidase
Authors: Harrison E. H. , Walusimbi-Kisitu M.
Published: December 2017

The properties and subcellular localization of fatty acyl-CoA oxidase (FAO) were studied in rat heart homogenates. After differential centrifugation, FAO was sedimentable and enriched in a “light-mitochondrial” fraction. FAO had a pH optimum of 8–9. Among straight-chain, saturated fatty acyl-CoAs, the enzyme showed a marked preference for medium chain substrates (C12 greater than C10 = C8 greater than C16 = C14 greater than C6) over a concentration range up to 100 microM. No activity was observed with C4-CoA. The apparent Michaelis constant (Km) for C12-CoA was 5-10 microM. After removal of nuclei by low-speed centrifugation, combined subcellular particle preparations were obtained by high-speed centrifugation and layered on linear density gradients of metrizamide. After density equilibration, FAO showed a symmetric distribution centered at p = 1.16–1.18, like that of the enzyme catalase, a marker for microperoxisomes. In contrast, enzyme markers for mitochondria, lysosomes, sarcolemma, and sarcoplasmic reticulum were recovered in low-density regions of the gradient. These results provide a direct demonstration of fatty acyl-CoA oxidase in cardiac tissue and its association with microperoxisomes.
Sympathetic changes during development of cardiac hypertrophy in aortic-constricted rats
Authors: Siri F. M.
Published: December 2017

Cardiac hypertrophy is frequently associated with sympathetic changes that include increased myocardial norepinephrine turnover, depleted myocardial norepinephrine stores, decreased myocardial responses to sympathetic nerve stimulation, and elevated plasma catecholamines. To better understand these events mechanistically, the time course of each was assessed in rat hearts subjected to aortic constriction-induced pressure overload. There was no evidence of increased left ventricular norepinephrine turnover in abdominal aortic-constricted rats, when compared with sham-constricted animals, during the first 3 days postoperatively. Moreover, their turnover rate constants tended to be lower during this period, then increased significantly by day 7. Plasma catecholamines were increased and left ventricular norepinephrine stores were decreased only on day 7. Heart rate responses to maximal sympathetic nerve stimulation were significantly reduced on the third postoperative day. Thus the decrease in norepinephrine stores coincided with changes in left ventricular norepinephrine turnover and plasma catecholamines, whereas the reduction in heart rate responses did not. This pattern suggests an initial reflex decrease in myocardial sympathetic tone, followed by baroreceptor resetting, with an eventual increase in general sympathetic outflow. The period of increasing catecholamine stimulation occurred after a relative left ventricular hypertrophy had developed but before a significant increase in absolute left ventricular mass. Thus catecholamines may still importantly contribute to the hypertrophy seen in this model.
Long-term hypotensive effect of beta-agonist in conscious dogs
Authors: Nuwayhid B. S. , Young D. B. , Tipayamontri U. , Montani J. P.
Published: December 2017

The purpose of this study was to investigate the arterial pressure response to long-term administration of beta-agonists in the chronically instrumented conscious animal model. Chronically instrumented dogs were given intravenous infusions of ritodrine (2 micrograms.kg-1.min-1) for a period of 2 wk. Several cardiovascular and renal parameters were monitored before, during, and after the ritodrine infusion, and renal function curves were constructed. After the 1st wk of infusion, a new steady state was reestablished, and this was characterized by hypotension, reduced plasma protein concentration, elevated cardiac output, expanded extracellular fluid space, and near normal levels of activity of renin-angiotensin-aldosterone systems. The renal function curve during ritodrine infusion shifted to the left with no change in slope. We propose the following: 1) the persistence of hypotension is most probably related to the resetting of the arterial pressure-kidney blood volume servocontrol mechanisms, and 2) the persistent elevation of cardiac output and reduction in peripheral resistance are most probably related to increased oxygen and nutrient demand during beta-agonist infusions.
Granulocyte-platelet interactions and platelet fibrinogen receptor exposure
Authors: Kornecki E. , Ehrlich Y. H. , Egbring R. , Gramse M. , Seitz R. , Eckardt A. , Lukasiewicz H. , Niewiarowski S.
Published: December 2017

We have examined the interaction of human granulocyte elastase with human platelets. Incubation of human platelets with human granulocyte elastase exposed active fibrinogen-binding sites as evidenced by 125I-labeled fibrinogen binding and spontaneous fibrinogen-induced platelet aggregation. The aggregation of platelets by fibrinogen occurred at low concentrations of human granulocyte elastase (0.5–1 microgram/ml). Platelets pretreated with human granulocyte elastase exposed an average of 10,500 fibrinogen binding sites per platelet, i.e., about one-third the number of binding sites exposed by optimal concentrations of ADP. With the use of a polyclonal antiplatelet membrane antibody, the glycoproteins IIb (GPIIb), IIIa (GPIIIa), and a 60,000-Da (60 kDa) protein (66 kDa in a reduced system) derived from GPIIIa were immunoprecipitated from the surface of detergent extracts of human 125I-radiolabeled platelets pretreated with increasing concentrations of human granulocyte elastase. Experiments performed by immunoblotting with use of polyclonal and monoclonal antibodies directed to GPIIIa showed that pretreatment of human platelets with granulocyte elastase resulted in the appearance of an additional proteolytic derivative of GPIIIa migrating with an apparent molecular mass of 120 kDa in a nonreduced system. GPIIIa appears to be the preferred substrate of elastase, since GPIIb was not degraded by human granulocyte elastase. We conclude that 1) the proteolytic action of human granulocyte elastase on platelet GPIIIa results in the formation of two major hydrolytic products, and 2) human granulocyte elastase exposes active fibrinogen-binding sites associated with the GPIIb/GPIIIa complex, resulting in direct platelet aggregation by fibrinogen.
Interrelation between end-systolic pressure-volume and pressure-wall thickness relations
Authors: Schipke J. D. , Alexander J. , Harasawa Y. , Schulz R. , Burkhoff D.
Published: December 2017

We predicted the shape of the end-systolic pressure-thickness relationship (ESPTR) by modeling the left ventricle as thick-walled sphere. To test the validity of the predicted relationships, we then measured the ESPTR over wide volume ranges in seven isolated blood-perfused canine hearts. Both simulation and experiments demonstrated that the ESPTR is curvilinear. However, within a physiological left ventricular systolic pressure range (80–150 mmHg), the ESPTR was described reasonably well by a straight line. Within that pressure range, changes in left ventricular contractile state, assessed by slope changes of the end-systolic pressure-volume relationship, were associated with almost parallel shifts in the ESPTR. In contrast, in a low pressure range (less than 80 mmHg), contractility changes were associated with slope changes of the ESPTR. We conclude that, in general, there are limitations in the application of ESPTR for assessing left ventricular contractility, but if the limitations are recognized and accounted for, then the ESPTR may be useful for assessing contractility changes in vivo.
Reflex activation of sympathetic nervous system by ANF in humans
Authors: Ebert T. J.
Published: December 2017

Recent studies in experimental animal preparations suggest that ANF might alter sympathetic nervous system function. In the present investigation, direct recordings of postganglionic muscle sympathetic nerve activity were obtained from the peroneal nerve of conscious human volunteers. These data and hemodynamic parameters were recorded before and during infusions of atrial natriuretic factor (ANF, 99–126) or placebo (isotonic saline) in 10 subjects. Base-line ANF (36.5 +/- 3.8) increased to 329 +/- 22 pg/ml during 20-min infusions of ANF (15 ng.kg-1.min-1). This did not alter heart rate or blood pressure but reduced central venous pressure (CVP) by 47 +/- 10% (P less than 0.01). Base-line-integrated sympathetic activity (14.4 +/- 2.4 bursts/min) increased 30 +/- 12% during ANF infusion (P less than 0.05). However, when CVP was fixed at control levels with head-down tilt or lower body positive pressure, sympathetic activity was unchanged from pre-ANF base-line levels. These data indicate that exogenous infusions of ANF reduced CVP and unloaded cardiopulmonary baroreceptors. This elicits reflex increases of muscle sympathetic efferent activity. When CVP is maintained at control levels, ANF does not alter sympathetic neural outflow to muscles.
Changes in AdSNA and arterial catecholamines to coronary occlusion in cats
Authors: Honda T. , Ninomiya I.
Published: December 2017

The relationship between adrenal (preganglionic) sympathetic nerve activity (AdSNA), cardiac sympathetic nerve activity (CSNA), and arterial catecholamines, i.e., epinephrine (Epi) and norepinephrine (NE), were analyzed during 200 s of occlusion of left anterior descending coronary artery in anesthetized cats. With coronary occlusion, AdSNA maximally increased to 168 +/- 20% (mean +/- SE) of the control value at 20 s and gradually decreased to 149 +/- 10% at 200 s. Mean CSNA (MCSNA), mean arterial pressure, and heart rate decreased significantly because of coronary occlusion. Arterial NE and Epi progressively increased from 0.54 +/- 0.05 and 0.29 +/- 0.03 ng/ml to 1.41 +/- 0.16 and 0.59 +/- 0.08 ng/ml at 3 min after the onset of occlusion, respectively. The correlation between AdSNA and arterial Epi (r = 0.71; P less than 0.01) and between AdSNA and arterial NE (r = 0.57; P less than 0.05) were significant, but the correlation between CSNA and arterial NE was not significant. On the other hand, in adrenalectomized cats, the increases in arterial Epi and NE did not appear during coronary occlusion. We concluded that, with coronary occlusion, AdSNA increased and, in turn, caused an increase in arterial Epi and NE.
No significant increase in O2 consumption of KCl-arrested dog heart with filling and dobutamine
Authors: Nozawa T. , Yasumura Y. , Futaki S. , Tanaka N. , Suga H.
Published: December 2017

In the cross-circulated dog hearts arrested with KCl, we examined the effects of left ventricular volume and dobutamine on the resting oxygen consumption (MVO2). The perfusion pressure of the excised heart was stable under the cross-circulation for 1-1.5 h with a dialyzer to normalize coronary venous KCl despite continuous coronary arterial injection of KCl. The resting MVO2 declined gradually during the first 10 min of cardiac arrest but changed little thereafter. The resting MVO2 at 5 min and 30 min of arrest were 30.5 +/- 9.3 (SD) and 23.8 +/- 12.9%, respectively, of unloaded MVO2 before arrest. The resting MVO2 after its stabilization was 1.02 +/- 0.42 ml O2.min-1.100 g ventricle-1 in the control. It was 1.12 +/- 0.48 ml O2.min-1.100 g ventricle-1 under a continuous infusion of dobutamine at rate of 10-25 micrograms/min. This change with dobutamine was statistically insignificant. The resting MVO2 was not affected by changes in left ventricular volume both before and under dobutamine. The present result implies that MVO2 for basal metabolism in a working dog heart is virtually constant regardless of ventricular volume and contractility.
Pressure-flow characteristics and nutritional capacity of coronary veins in dogs
Authors: Cohen M. V. , Matsuki T. , Downey J. M.
Published: December 2017

To examine the hemodynamic interdependence of coronary arteries and veins, great cardiac vein (GCV) and left anterior descending (LAD) coronary artery flows of dogs were measured. Although they were not different under base-line conditions, 42.9 +/- 4.1 and 34.9 +/- 5.2 ml/min, respectively, LAD occlusion caused only a 56% decrease in GCV flow, whereas peak GCV flow during reactive hyperemia consistently underestimated peak LAD flow by nearly 40%. The measured hemodynamic data were very closely predicted by a simple model that assumed the presence of a low-resistance venous collateral anastomotic pathway between the GCV and veins outside the LAD territory. The resistance of the venous collaterals averaged 9.9 +/- 3.0% of LAD resistance. Therefore, GCV flow does not solely represent LAD collateral flow when the LAD is occluded, nor is it a reliable indicator of changes in LAD perfusion patterns. Nutritional myocardial perfusion assessed with 133Xe washout decreased from 0.86 +/- 0.16 to 0.13 +/- 0.02 ml.min-1.g-1 after LAD occlusion, whereas retroperfusion of the GCV with arterial blood enhanced washout by 85% to 0.23 +/- 0.03 ml.min-1.g-1 (P less than 0.005). Retroperfusion was inefficient, however, since only 10% of the isotope injected into the GCV gained access to the myocardium.
Cytoplasmic Mg2+ concentration in platelets: implications for determination of Ca2+ with aequorin
Authors: Ware J. A. , Smith M. , Fossel E. T. , Salzman E. W.
Published: December 2017

The concentration of cytoplasmic ionized Mg2+ ([Mg2+]i) varies considerably among different cell types. It has not been measured in platelets. Incorrect estimates of this value could markedly affect many intracellular investigations, including calibration of measurements of platelet cytoplasmic ionized Ca2+ concentration ([Ca2+]i) with the photoprotein aequorin and other Ca2+-sensitive probes. [Mg2+]i was measured in washed, gel-filtered human platelets suspended in modified Tyrode buffer by two methods: 31P-nuclear magnetic resonance (NMR) spectroscopy of intact platelets and null-point titration in platelets selectively permeabilized with digitonin. The 31P-NMR spectra demonstrated that the [Mg2+]i, as calculated from the chemical shift values of ATP resonances, was 0.23 +/- 0.02 (SD) mM in unstimulated platelets. The mean [Mg2+]i as determined by null-point titration was 0.3 +/- 0.1 mM (range: 0.1-0.6 mM). When this [Mg2+]i value was used to construct a Ca2+-calibration curve for aequorin, the indicated [Ca2+]i values in resting and stimulated platelets were lower than those obtained from curves based on previously assumed values for [Mg2+]i (1.0-1.25 mM). This finding largely resolves the discrepancy between resting [Ca2+]i as determined by aequorin or by quin2, fura-2, and indo-1.
Subcellular electrolyte shifts during in vitro myocardial ischemia and reperfusion
Authors: Walsh L. G. , Tormey J. M.
Published: December 2017

Isolated perfused rabbit right ventricular wall was studied with electron probe microanalysis (EPMA) under three conditions: 1) control (37 degrees C, 1.2 Hz), 2) 60 min global ischemia, and 3) ischemia plus 5 min of reperfusion. After 60 min of ischemia, only one cell population was evident; the variance of intracellular electrolyte concentrations was the same as in controls. When compared with controls, there was no change in Ca concentration within any region of the cell, but mitochondria were swollen with K-rich fluid. Two cell populations were evident after 5 min of reperfusion. The severely injured cells were markedly swollen, exhibited hypercontraction bands, and had electrolyte profiles similar to extracellular fluid. The moderately injured cells were normal in appearance, still retained electrolyte gradients, but had elevated Na and Cl concentrations in all compartments. Cell Ca did not increase in the moderately injured cells, but the region of the cell containing the sarcoplasmic reticulum (SR) lost 90% of its Ca. Accompanying this loss were large increases in myofibrillar and mitochondrial Ca concentration. It appears that release of SR Ca, loss of SR Ca-accumulating capacity, and increased intracellular Na are the principal electrolyte shifts in functional cells during early reperfusion.
Acute changes in forearm venous volume and tone using radionuclide plethysmography
Authors: Manyari D. E. , Malkinson T. J. , Robinson V. , Smith E. R. , Cooper K. E.
Published: December 2017

In this investigation blood pool scintigraphy was validated as a method to study acute changes in human forearm veins. Changes in regional forearm vascular volume (capacity) and the occluding pressure-volume (P-V) relationship induced by sublingual nifedipine (NIF) and nitroglycerin (GTN) were recorded in 16 patients with simultaneous data collection by the radionuclide and the mercury-in-rubber strain-gauge techniques. The standard error of estimate (Syx) between successive control measurements using the radionuclide method was 3.1% compared with 3.2% for the strain-gauge method. The venous P-V curves were highly reproducible using both techniques. Strain gauge and radionuclide measurements of acute changes in forearm venous volume correlated well (r = 0.86; Syx = 7%, n = 156). After 20 mg of NIF or 0.6 mg of GTN, mean heart rate increased from 71 +/- 10 to 77 +/- 9 and from 68 +/- 10 to 75 +/- 11 beats/min, respectively, and group systolic blood pressure decreased from 128 +/- 22 to 120 +/- 19 and from 136 +/- 18 to 126 +/- 23 mmHg, respectively (P less than 0.05). At venous occluding pressures of 0 and 30 mmHg, the forearm vascular volume did not change after NIF (2 +/- 4 and -1 +/- 4%; P greater than 0.05), whereas it increased after GTN (8 +/- 5 and 12 +/- 7%; P less than 0.001). The forearm venous P-V relationship did not change after NIF, whereas a significant rightward shift (venodilation, with an increase in unstressed volume) occurred after GTN.(ABSTRACT TRUNCATED AT 250 WORDS)
Enhanced vascular alpha-adrenergic neuroeffector system in diabetes: importance of calcium
Authors: White R. E. , Carrier G. O.
Published: December 2017

Mesenteric arteries from streptozotocin (STZ)-diabetic rats developed greater contractile force in response to norepinephrine and related alpha-agonists than arteries from age-matched controls. Subsequent experiments attempted to define the mechanisms underlying these findings. Transmural nerve stimulation of mesenteric arteries from both groups of animals revealed a similar optimal frequency and voltage of stimulation; however, arteries from STZ-diabetic rats developed greater contractile force than controls. Second, determination of selective alpha-adrenergic antagonist affinities (pA2 values) revealed qualitatively similar postjunctional alpha 1-adrenoceptors in both groups of arteries. Third, disruption of the endothelium did not abolish the enhanced responsiveness of arteries from STZ-diabetic rats. In contrast, the increased vascular responsiveness in STZ-diabetes was associated with a greater dependency on extracellular calcium, with no change in the response to alpha-agonist-induced release of calcium from cellular stores. Thus the enhanced responsiveness of mesenteric arteries from STZ-diabetic rats to alpha-adrenergic agonists cannot be attributed to neuronal deterioration, altered postjunctional alpha-adrenoceptor subtypes, endothelium degeneration, or enhanced release of intracellular calcium but is associated with a greater dependency on extracellular calcium.
Total and regional blood flows in vascularized skeletal muscle grafts in rabbits
Authors: Burton H. W. , Stevenson T. R. , Dysko R. C. , Gallagher K. P. , Faulkner J. A.
Published: December 2017

The transplantation of whole skeletal muscles is a common clinical procedure. Although atypical blood flows have been reported in small free muscle grafts, the blood flow of large neurovascular-intact (NVI) and neurovascular-anastomosed (NVA) grafts have not been measured. Because the maximum specific force (N/cm2) of NVI and NVA grafts is 65% that of control muscles, we hypothesized that total and regional blood flows (ml.min-1.100g-1) of NVI and NVA grafts at rest and during twitch contractions are significantly lower than lower flows of control muscles. In rabbits, blood flows of control rectus femoris (RFM) muscles and NVI and NVA grafts of RFM muscles were measured by the radioactive-microsphere technique. In control muscles, blood flow increased linearly from 6.8 +/- 1 ml.min-1.100 g-1 at rest to 64.4 +/- 7 ml.min-1. 100 g-1 at a stimulation frequency of 3 Hz with no further increase at 4 Hz. Total blood flows in grafts were not different from the control RFM muscle values, except for a higher resting flow in NVA grafts and a lower flow at 3 Hz in NVI grafts. Minor variations in regional flows were observed. We conclude that the operative procedures of grafting and repair of blood vessels affect the vascular bed of muscles minimally, and the deficits observed in grafts do not arise from inadequate perfusion.
In vivo bioassay of endothelium-derived relaxing factor
Authors: Kontos H. A. , Wei E. P. , Marshall J. J.
Published: December 2017

We devised a technique for the in vivo assay of endothelium-derived relaxing factor (EDRF) from cerebral microvessels. We used anesthetized cats equipped with two cranial windows. One window (assay window) was subjected to muscarinic blockade with atropine to inhibit the direct effects of acetylcholine. EDRF production was induced in the donor window by superfusion with acetylcholine. The superfusate was then directed through the assay window with a delay of 6 s where it caused vasodilation equal to that seen in the donor window. The dilation was eliminated by lengthening the transit time from the donor to the assay window to greater than 2 min or by muscarinic blockade with atropine in the donor window but not by indomethacin in the donor window. It was also inhibited by hemoglobin and methylene blue or by selective damage to the endothelium of the vessels in the donor window with topical application of arachidonate or hydrogen peroxide. We conclude that the vasoactivity of the superfusate is due to EDRF released by acetylcholine from cerebral microvessels.
Effects of ischemic conditions and reperfusion on depolarization-induced automaticity
Authors: Mohabir R. , Ferrier G. R.
Published: December 2017

The inducibility of slow-response automaticity was assessed during ischemic conditions and reperfusion by application of extracellular current. Isolated canine Purkinje fibers were depolarized to membrane potentials less than -65 mV to elicit depolarization-induced automaticity (DIA). Ischemic conditions increased the cycle length of DIA and, in some tissues, prevented sustained DIA or completely abolished DIA. The magnitude of depolarization required to elicit DIA also increased. Inhibition of DIA occurred at a time when action potential plateaus were abbreviated. The effect of reperfusion on DIA was biphasic. Initial reappearance of DIA was followed by inhibition and reduction of the membrane potential range over which DIA could be elicited. Plateaus of action potentials initiated at high membrane potential were abbreviated at this time. DIA returned again as reperfusion effects dissipated. Phasic changes in the inducibility of DIA may represent changes in availability of the slow inward current and may regulate the timing and types of arrhythmic activity occurring with ischemia and reperfusion.
Flow-mediated dilation attenuates constriction of large coronary arteries to serotonin
Authors: Lamping K. G. , Dole W. P.
Published: December 2017

We tested the hypothesis that flow-mediated endothelium-dependent dilation can attenuate humorally mediated constriction of large coronary arteries in vivo. Accordingly, we measured constriction of large coronary arteries to serotonin when flow was allowed to increase and when flow was constant in the presence and absence of endothelium. The left anterior descending coronary artery of anesthetized dogs was perfused at constant pressure (100 mmHg) and diameter measured with an ultrasonic dimension gauge. Coronary flow was measured with an in-line electromagnetic flow probe. Flow-mediated dilation was demonstrated by measuring diameter (D) after increased flow in response to adenosine (1 mg/min ic). Adenosine (n = 9) increased flow (341 +/- 69%) and resulted in large artery dilation [diameter change (delta D) = 101 +/- 54 microns], which was abolished by maintaining constant flow (distal snare) or by removing endothelium. Serotonin (n = 9, 50 micrograms/min ic) increased flow (298 +/- 45%) while simultaneously decreasing large artery diameter (delta D = -58 +/- 22 microns). When flow was kept constant, serotonin produced a greater constriction (delta D = -173 +/- 29 microns). After the removal of endothelium (n = 10), constrictor responses to serotonin were similar when flow increased (delta D = -84 +/- 13 microns) and when flow was kept constant (delta D = -79 +/- 23 microns). We conclude that flow-mediated dilation of large coronary arteries can attenuate constriction to serotonin and that this effect is dependent on endothelium.
Acetate causes endothelium-independent increases in cyclic AMP in rat caudal artery
Authors: Daugirdas J. T. , Swanson V. , Islam S. , Nutting C. , Kim D. D. , Wang X. A. , Fiscus R. R.
Published: December 2017

The mechanism of the vasorelaxant action of acetate is unknown. Because cyclic nucleotides have been linked to vasorelaxation in vascular smooth muscle, we studied the effects of acetate on tissue adenosine 3',5'-cyclic monophosphate (cAMP) and guanosine 3',5'-cyclic monophosphate (cGMP) levels in rat caudal artery. Acetate (4 mM) induced an increase in tissue cAMP levels (control: 5.1 +/- 0.67, acetate: 7.1 +/- 0.97 pmol/mg protein, P less than 0.05), with the increase noted as early as 15–30 s after acetate exposure, and peaking at 60 s. The time course of the cAMP response was compatible with the vasorelaxant effect of acetate against an arginine vasopressin (AVP, 2 X 10(-9) M) contraction. Both the increase in cAMP and the vasorelaxant effect were completely blocked by 10(-3) M 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid (DIDS). Acetate increased cAMP levels in 3-isobutyl-1-methylxanthine (IBMX)-treated tissue with an effective concentration producing 50% of the maximum response (EC50) of 1.5 mM, similar to the relaxant EC50 (without IBMX) of 2.2 mM against an AVP contraction. In other experiments, the effect of acetate on cAMP was shown to be independent of endothelium. In contrast, acetate had no effect on tissue cGMP levels, whether the endothelium was present or absent. The results suggest that acetate causes an increase in tissue cAMP levels that is not dependent on presence of a functioning endothelium. The changes in cAMP may be contributory to the vasorelaxant effect of acetate in the caudal artery.
Area of the aortic pressure-flow loop measures energy storage by the proximal arteries
Authors: Appleyard R. F. , Campbell K. B. , Ringo J. A.
Published: December 2017

We show that power measured by the area of the pressure-flow loop (APQ) is directly proportional to reactive power [Im(W)], which measures pulsatile energy storage in the proximal arteries. Analytically, Im(W) differs from APQ by K.2 pi, where K is a postulated constant of proportionality. To determine the value of K, 338 heartbeats obtained from 8 dogs under a wide range of hemodynamic conditions were analyzed. The relationship between APQ and Im(W) remained highly linear (r = 0.98), and the pooled value of K was -1.19 +/- 0.01. For the individual dogs, values of K differed at most by +/- 9% from its average value. There was also a small offset in the relationship between APQ and Im(W), probably caused by truncating the calculation of Im(W) at the 10th harmonic. Ignoring the small differences in the values of K and the offset, we found that APQ still proved to be an excellent predictor of Im(W). We also found that APQ was sensitive to changes in heart rate, left ventricular stroke output, and peripheral resistance. This reflects the dependence of pulsatile energy storage on these variables and indicates that APQ cannot serve as an index for changes in just the reactive properties of the proximal arteries.
Blood oxygen content estimated from PO2, PCO2, and pH
Authors: Belanger S. F. , Katz S. A. , Huang A. H. , Feigl E. O.
Published: December 2017

Oxygen content of blood (265 samples, 25 dogs) from two experimental groups was estimated from measurements of blood PO2, PCO2, pH, hemoglobin, and body temperature with the computational subroutines of Olszowka and Farhi (6). Each computed value was compared with the corresponding oxygen content measured directly by a galvanometric oxygen fuel cell (Lex-O2-Con analyzer). The computed values had consistent errors when compared with the corresponding fuel cell determinations. Linear regression of fuel cell determinations on the corresponding computed values was used to obtain a corrected estimate of oxygen content. When the linear regression correction procedure was performed within each of 25 dogs, the resultant estimates were substantially improved over a lumped correction. The mean absolute value of the difference between the corrected calculated value within an individual dog and the corresponding oxygen fuel cell content determination was 0.38 +/- 0.28 (6 anesthetized dogs, 76 samples) and 0.17 +/- 0.15 (19 awake dogs, 189 samples) (SD) vol% for the two experimental groups. It is concluded that blood oxygen content may be accurately estimated from PO2, PCO2, and pH when appropriately corrected. The advantage is that only a small subset of the total number of blood samples needs to be analyzed with the oxygen fuel cell.
Myogenic activity in isolated subepicardial and subendocardial coronary arterioles
Authors: Kuo L. , Davis M. J. , Chilian W. M.
Published: December 2017

The goal of this study was to examine myogenic responses of isolated porcine subepicardial and subendocardial arterioles (80–100 micron in diameter) within physiological ranges of intraluminal pressure. Arterioles were located by perfusion with india ink-gelatin solution then dissected and cannulated with glass micropipettes. Intraluminal pressure was altered in 20-cmH2O steps over the range of 20–140 cmH2O. IN physiological salt solution (36–37 degrees C), the coronary arterioles developed spontaneous tone and exhibited myogenic responses. At the lower pressures (20–60 cmH2O), subendocardial arterioles responded passively (diameter decreased from a control diameter at 60 cmH2O), whereas subepicardial arterioles maintained their diameters. At higher pressures (100–140 cmH2O), both subepicardial and subendocardial arterioles demonstrated myogenic constriction, but subepicardial arterioles demonstrated greater myogenic constriction than subendocardial arterioles. This implies that myogenic autoregulation in subepicardial arterioles is better than that in the subendocardial arterioles at both low and high pressures. In the presence of nitroprusside (10(-4) M), all arterioles responded to pressure changes passively, and there were no differences between subepicardial and subendocardial vessels. The functional integrity of the endothelium was verified by relaxation to substance P (10(-7) M). This is the first in vitro study to demonstrate coronary myogenic activity and transmural differences in these arteriolar responses. Our data support the concept that myogenic mechanisms in 80 to 100-micron arterioles may actively contribute to autoregulation of coronary blood flow.
Errors in microsphere determination of cardiac output: a computer simulation in fetal sheep
Authors: Hope I. D. , Huikeshoven F. J. , Gilbert R. D. , Power G. G. , Longo L. D.
Published: December 2017

Through use of a compartmental model, we simulated the measurement of cardiac output and distribution by means of radioactively labeled microspheres in fetal lambs with weights between 0.5 and 3 kg. A systematic error in measured cardiac output caused by artifactual changes in blood volume caused by the injection and withdrawal of fluids during the procedure was less than 5% for fetal weights greater than or equal to 1 kg but increased for fetal weights less than 1 kg and when hypovolemia was simulated at all fetal weights. Sensitivity analysis disclosed no significant effect of changes in vascular resistance. We examined the effects of recirculation of microspheres and found no significant increase in error in the measured value of cardiac output due to 20% recirculation of all spheres entering a single isolated organ system; however, errors between 7 and 14% were observed with simulations of 20% recirculation in more than one compartment simultaneously. Recirculation also introduced significant errors in the measured distribution of cardiac output in certain cases. The effect on the measured cardiac output of a temporary change in the true cardiac output was dampened by the artifactual blood volume changes mentioned above and the fact that the measurement is a time-weighted average. We also evaluated four different experimental designs. We conclude that the microsphere technique provides a remarkably reliable means of quantifying cardiac output and individual organ flow in the fetus. The nonrandom errors inherent in the procedure examined in this study are of the order of 10%, which is likely to be less than the moment-to-moment variation in the true cardiac output.
Shunting of leukocytes in rabbit tenuissimus muscle
Authors: Ley K. , Meyer J. U. , Intaglietta M. , Arfors K. E.
Published: December 2017

Leukocyte distribution was studied in 58 arterioles and capillaries constituting eight networks in the fascia adjacent to the rabbit tenuissimus muscle. Fluorescence video microscopy (acridine red) and digital image processing were used to visualize the leukocytes. Leukocyte concentration in the transverse arterioles leaving the muscle proper to irrigate the fascia was significantly elevated to 143 +/- 13% (mean +/- SE) of the systemic count. Leukocytes were found to further accumulate along the arteriolar tree, reaching 244 +/- 16% of systemic in the most remote branches. Leukocyte accumulation in the connective tissue can be calculated to lead to a decrease of leukocyte concentration in muscle capillaries to 89% of the systemic value. This shunting effect may be important in preventing leukocyte-induced capillary obstruction. At individual arteriolar bifurcations, leukocytes were found to preferentially enter the downstream branch with higher flow rate (regression coefficient 1.11 +/- 0.04, n = 100). This preferential distribution is quantitatively sufficient to account for the observed leukocyte distribution in the network.
Regional adrenal blood flow during hypoxia in anesthetized, ventilated dogs
Authors: Nishijima M. K. , Breslow M. J. , Raff H. , Traystman R. J.
Published: December 2017

The effect of hypoxic hypoxia (HH) and carbon monoxide hypoxia (COH) on adrenal medullary (MQ) and cortical (CQ) blood flow (radiolabeled microsphere technique) was studied in pentobarbital sodium-anesthetized, mechanically ventilated dogs. Animals were exposed to 60 min of hypoxia (arterial O2 content 8 vol%) induced by adding either nitrogen (HH, n = 6) or carbon monoxide (COH, n = 6) to the inspired gas. Whole adrenal Q and CQ increased by 70 and 50%, respectively, with HH but were unchanged during COH. MQ, however, increased threefold during both HH and COH. HH and COH both increased arterial levels of epinephrine, corticosteroids, and adrenocorticotropic hormone (ACTH). To determine whether the increase in CQ during HH was because of HH-induced increases in mean arterial blood pressure (MAP, approximately 20 mmHg), an additional group of animals (n = 6) was exposed to HH but had MAP maintained at control levels using a pressurized-bottle system. MAP control did not alter the CQ response to HH. We conclude that MQ appears to be associated with medullary secretory activity during hypoxia and that HH and COH stimulate adrenal medullary secretion equally. In contrast, CQ increases only with HH, despite similar increases in ACTH and corticosteroid levels during HH and COH, suggesting that an alternative mechanism is responsible for increased cortical blood flow during HH.
Two structural states of Z-bands in cardiac muscle
Authors: Goldstein M. A. , Michael L. H. , Schroeter J. P. , Sass R. L.
Published: December 2017

We have compared the form and dimensions of the Z-band lattice in rat papillary muscle fixed at rest with and without ethylene glycol-bis(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid (EGTA) using electron microscopy and optical diffraction. In unstimulated muscle, the Z-band lattice form called basket weave predominated, and the Z-spacing (defined as the repeat distance of a tetragonal array of cross-cut thin filaments from the same sarcomere) was 23.93 +/- 0.37 nm. Muscles exposed to EGTA exhibited the small square-lattice form, and the Z-spacing was 20.50 +/- 0.19 nm. The Z-spacings in the two lattice forms were similar in cardiac and skeletal muscles such that the decrease in Z-spacing in the transition from basket weave to small square in this study was similar to the increase in Z-spacing previously demonstrated in skeletal muscle in the transition from small square to basket weave. The Z-lattice form and dimensions in unstimulated cardiac muscle resembled those in tetanized skeletal muscle. These findings are consistent with the higher resting tension in cardiac muscle and suggest that Ca2+ may be important for the maintenance of the expanded Z-lattice form.
Dimethylsulfoxide prevents chemoattractant-induced leukocyte adherence
Authors: Sekizuka E. , Benoit J. N. , Grisham M. B. , Granger D. N.
Published: December 2017

The objective of this study was to determine whether dimethylsulfoxide (DMSO) influences chemoattractant-induced leukocyte adherence in the intestinal microcirculation. The distal colon of Sprague-Dawley rats was prepared for intravital microscopic observation of 25-35 microns diameter venules located in the muscularis externa. The number and average velocity of rolling leukocytes and the number of leukocytes adherent to the venular endothelial surface were determined from recorded video images. After a control period of observation, either N-formyl-methionyl-leucyl-phenylalanine (FMLP) or leukotriene B4 (LTB4) was added to the serosal superfusion solution. Both FMLP (1 microM) and LTB4 (1 microM) consistently caused leukocytes to adhere to venular endothelium. DMSO, at concentrations ranging between 2.5 and 140 mM, inhibited FMLP-induced leukocyte adherence in a dose-related manner. LTB4-induced leukocyte adherence was also significantly attenuated by DMSO. Leukocyte rolling velocity and leukocyte flux were not affected by DMSO. These results indicate that DMSO significantly inhibits leukocyte adherence at concentrations commonly used for its hydroxyl radical scavenging properties.
Effect of myocardial ischemia on hemodynamic response to carotid occlusion
Authors: Billman G. E. , Marsh D. H.
Published: December 2017

Fourteen mongrel dogs were anesthetized and instrumented to measure arterial pressure (AP), left ventricular pressure (LVP), aortic blood flow, and heart rate (HR). Hydraulic occluders were placed around the left anterior descending (LAD, n = 9) and left circumflex (LCC, n = 14) coronary arteries. A bilateral carotid occlusion (BCO) was made before and during either anterior (LAD occlusion) or posterior (LCC occlusion) ischemia. Posterior ischemia significantly (P less than 0.01) reduced the BCO-induced increases in mean AP (by 44.3 +/- 7.3%), systolic LVP (by 65.5 +/- 6.9%), first derivative of LVP (dLVP/dt, by 95.7 +/- 44.3%), and aortic resistance (by 117.7 +/- 26.9%). In contrast, anterior ischemia failed to alter significantly the hemodynamic response to BCO. Bilateral vagotomy attenuated or eliminated many of the effects of posterior ischemia on the BCO response. In fact, the change in aortic resistance was no longer affected by the ischemia and increased to the same extent, as noted during the control BCO. However, mean AP (38.7 +/- 6.8%), systolic LVP (40.3 +/- 8.7%), and dLVP/dt (62.4 +/- 11.0%) remained significantly reduced when compared with the control (no coronary occlusion) response. These data suggest that 1) posterior ischemia elicits a greater reduction in the BCO response than anterior ischemia, and 2) vagal afferents as well as depression of contractile function may both contribute to the BCO response inhibition noted during posterior ischemia.
Potassium-induced relaxation of arteries in hypertension: modulation by extracellular calcium
Authors: Rinaldi G. , Bohr D. F.
Published: December 2017

Smooth muscle relaxation due to activation of Na+-K+-adenosinetriphosphatase (ATPase) (K+ relaxation) was studied in isolated tail arteries from stroke-prone spontaneously hypertensive (SHRSP) and Wistar-Kyoto (WKY) rats. Exposure to K+ (7 mM) relaxed a norepinephrine (1 microM) contraction induced in K+-free physiological salt solution (PSS) by 46 +/- 3% in WKY and by 81 +/- 3% in SHRSP. Incubation with monensin (10 microM) augmented the K+-relaxation in WKY to 61 +/- 5%. Incubation with amiloride (10 microM) or with low-Na+ (10 mM) PSS attenuated the K+ relaxation in SHRSP to 34 +/- 3 and 5 +/- 2%, respectively. Incubation with high-Ca2+ (6.6 mM) PSS attenuated the K+ relaxation in WKY to 25 +/- 3% but resulted in only a slight decrease in the relaxation in SHRSP (to 73 +/- 2%). We conclude 1) that a greater Na+ leakiness of the plasma membrane in SHRSP than in WKY while the Na+ pump is inactive in K+-free PSS can explain the greater relaxation observed when the Na+ pump is reactivated and 2) that the Na+ leakiness of the membrane is more attenuated by Ca2+ in the WKY than in the SHRSP. We hypothesize that this Ca2+ effect reflects a normally large amount of this ion that can be bound to and thereby stabilize the membrane of the WKY, decreasing its permeability to Na+. The membrane of the SHRSP is deficient in its Ca2+-binding sites. Hence the added Ca2+ does not further stabilize its membrane.(ABSTRACT TRUNCATED AT 250 WORDS)