ISSN:0009-7330    

出版商:OVID    

年代:1972

数据来源: OVID

ISSN:0009-7330    

出版商:OVID    

年代:1972

数据来源: OVID

摘要:

The purpose of this investigation was to learn what part of the carotid sinus baroreceptor response is attributable to the gross mechanical properties of the wall and what part to the receptor elements. Static pressure forcings were applied to an isolated dog carotid sinus preparation while baroreceptor nerve activity was recorded; carotid sinus deformation was measured from still photographs taken during the experiment. Pressure–nerve activity data were obtained from four dogs and pressure-deformation data from another five dogs. The average electrical power in the nerve signal was used as the measure of nerve activity, and strain-energy density, a scalar quantity, was selected as the best indicator of the mechanical state of the sinus wall. Strain-energy density was calculated by measuring the circumferential and the longitudinal strains and by estimating the corresponding stresses in accordance with a thin-walled, axially symmetric model. The pressure–nerve activity data followed an S-shaped pattern, but the pressure–strain-energy density data were linear over the pressure range of 50 to 250 mm Hg. A curve of strain-energy density vs. nerve activity constructed from these two graphs, with pressure as the parametric variable, showed a linear relationship between nerve activity and strain-energy density over the pressure range of 75 to 175 mm Hg, but the slope of the curve rapidly went to zero with increasing pressure. We concluded that the nonlinearity in the pressure–nerve activity relationship was primarily due to the inability of the receptor elements to respond to increasing wall strains.

ISSN:0009-7330    

出版商:OVID    

年代:1972

数据来源: OVID

摘要:

The ventricles of open-chest anesthetized dogs were stimulated at a constant frequency to simulate ventricular parasystole. When the stimulation frequency was approximately half the spontaneous discharge frequency of the sinoatrial node, the natural pacemaker became synchronized with the artificial pacemaker. During such entrainment, the parasystolic rhythm resembled bigeminy with fixed coupling. Numerous instances of concealed bigeminy were also observed. Characteristic changes in arterial blood pressure always accompanied the repetitive ectopic beats, and these changes in blood pressure, acting mainly through the baroreceptor reflexes, were principally responsible for the synchronization. When the cardiac autonomic neural pathways were interrupted, synchronization usually could not be achieved. The biological feedback control system producing synchronization may be represented as follows. (1) The difference in timing between the firings of the sinoatrial node and the ectopic focus is the coupling interval. (2) This interval is a determinant of the stroke volumes of the premature and the postextrasystolic beats. (3) The stroke volumes affect the arterial blood pressure. (4) The level of blood pressure influences the neural activity in the baroreceptor reflex arc. (5) This activity in turn alters the frequency of the sinoatrial node. (6) Finally, sinoatrial nodal frequency affects the coupling interval to close the feedback loop.

ISSN:0009-7330    

出版商:OVID    

年代:1972

数据来源: OVID

摘要:

The urinary excretion of kallikrein was examined in rats whose mineralocorticoid level was increased by the administration of deoxycorticosterone or a low-sodium diet and decreased by adrenalectomy. Administration of deoxycorticosterone by injection or by subcutaneous implantation of pellets resulted in a threefold increase in kallikrein excretion after 10–30 days (P< 0.01). Low-sodium intake produced a twofold increase in kallikrein excretion after 2 and 4 weeks (P< 0.01). Urine volume and blood pressure were normal and unchanged throughout the study. Sodium excretion was unaltered by deoxycorticosterone but was essentially zero during low-sodium intake. Adrenalectomized rats excreted less than half the kallikrein of shamoperated control rats (P< 0.01). These data show a direct relationship between mineralocorticoids and kallikrein excretion and suggest that mineralocorticoids are a primary factor regulating the urinary excretion of kallikrein in rats.

ISSN:0009-7330    

出版商:OVID    

年代:1972

数据来源: OVID

摘要:

The octapeptide analogues 8-Cys-AII, 8-Ile-AII, 4-Phe-8-Tyr-AII, andp-fluoro-4-Phe-AII were potent competitive antagonists of angiotensin I and II (AI and AII) in rat uterus strips, whereas the decapeptide analogues 4-Phe-8-Tyr-AI and 8-Ile-AI were weak antagonists, 8-Cys-AII and 8-Ile-AII were potent antagonists of the rise in blood pressure induced by angiotensin, although 4-Phe-8-Tyr-AII andp-fluoro-4-Phe-AII were less potent antagonists. AI was rapidly converted and was equipotent to AII in vivo, but 8-Ile-AI was a hundred times less potent than 8-Ile-AII. However, some conversion of 8-Ile-AI did occur, since SQ 20881 (an inhibitor of angiotensin-converting enzyme) markedly diminished the All antagonistic action of 8-Ile-AI. The decapeptides AI, 8-Ile-AI, and 4-Phe-8-Tyr-AI were potent competitive antagonists of the hydrolysis of hippurylhistidylleucine by converting enzyme in vitro. Infusion of the octapeptide and the decapeptide angiotensin analogues resulted in a significant lowering of the blood pressure in anesthetized rats treated with phenoxybenzamine and propranolol and made acutely hypertensive by unclamping a renal pedicle that had been temporarily occluded. The decapeptide analogues, therefore, can function as inhibitors of angiotensin-converting enzyme and simultaneously generate octapeptide antagonists in vivo.

ISSN:0009-7330    

出版商:OVID    

年代:1972

数据来源: OVID

摘要:

The mechanisms which determine the response of stroke volume to mild, moderate, and severe exercise were compared in nine dogs running on a level treadmill. The dogs ran for 3-minute periods at 3–4 mph (mild exercise), 6–8 mph (moderate exercise), and 10–14 mph (severe exercise). Heart rate increased from a standing control value of 107 ± 6 beats/min to 191 ± 10 beats/min in mild, 221 ± 8 beats/min in moderate, and 263 ± 9 beats/min in severe exercise. Stroke volume increased 14%, 19%, and 15% for mild, moderate, and severe exercise, respectively. During mild exercise, left ventricular internal diameter decreased at end-systole but was unchanged at end-diastole. During moderate and severe exercise, end-diastolic diameter increased consistently as did left ventricular end-diastolic pressure. It was concluded that, despite extremely high heart rates, stroke volume increased during exercise. The augmentation in stroke volume was due to the combined effects of an increase in contractility, caused by increased sympathetic nervous system activity, and the operation of the Frank-Starling mechanism.

ISSN:0009-7330    

出版商:OVID    

年代:1972

数据来源: OVID

摘要:

An age-dependent study of plasma renin activity (PRA), kidney renin activity (KRA), and plasma renin substrate was carried out in rats with spontaneous hypertension during the prehypertensive, the early hypertensive, and the established hypertensive phases of their disease. PRA and KRA were both significantly elevated before and during the initial phase of hypertension and normal or subnormal during the established phase. In normal controls, neither KRA nor PRA was significantly different during the entire growth period. Plasma renin substrate was elevated throughout the growth period in rats with hypertension. This relationship between renin and blood pressure suggests that renin may play a primary role, possibly along with other factors, in the initiation of hypertension in rats with spontaneous hypertension.

ISSN:0009-7330    

出版商:OVID    

年代:1972

数据来源: OVID

摘要:

The role of sympathetic nerves and circulating catecholamines in mediating the renal vascular response to severe exercise was examined in normal dogs and dogs with experimental heart failure, using paired normal and denervated kidneys. In normal dogs, mean arterial blood pressure increased gradually from 97 ± 4 to 137 ± 6 mm Hg, renal blood flow remained at control levels, and renal vascular resistance rose from 0.57 ± 0.04 to 0.84 ± 0.15 mm Hg/ml min−1during peak steady-state exercise. The increase in resistance was similar in the denervated renal bed and persisted after alpha-receptor blockade. Exercise in dogs with heart failure increased mean arterial blood pressure slightly from 103 ± 4 to 111 ± 5 mm Hg. In the innervated kidney, blood flow dropped precipitously from 148 ± 6 to 46 ± 9 ml/min, and renal resistance increased from 0.73 ± 0.08 to 3.35 ± 0.53 mm Hg/ml min−1. In the denervated kidney, renal blood flow decreased from 174 ± 12 to 120 ± 1 ml/min, and resistance increased from 0.59 ± 0.07 to 0.94 ± 0.09 mm Hg/ml min−1. After alpha-receptor blockade, the decrease in flow and the increase in resistance to the denervated kidney were further attenuated. Thus, in normal, healthy dogs, the contribution of adrenergic mechanisms to renal vascular regulation appears to be minimal; blood flow remains constant in the presence of elevated pressure, suggesting that autoregulation is responsible for the elevated renal resistance during exercise. In dogs with experimental heart failure, intense renal sympathetic vasoconstriction prevails throughout exercise; the major portion of this response is neurally mediated, with an additional contribution by circulating catecholamines.

ISSN:0009-7330    

出版商:OVID    

年代:1972

数据来源: OVID

摘要:

Repeated measurements of cerebral blood flow distribution were made in man at 1-minute intervals: a133xenon solution was injected into the internal carotid artery, and gamma radiation was recorded extracranially in multiple hemispheric regions. In each study, a full-length133xenon clearance curve was recorded for 15 minutes and a series of about 15 equal isotope injections separated by 1-minute intervals was given. Following each injection in this multibolus series, a sudden increase in activity was recorded from each brain region. The complete series yielded a slowly rising sawtooth curve for each region; the perpendicular heights of these curves are a measure of the amount of isotope arriving at each region of the brain following each injection and this amount of isotope is proportional to the flow in the region, according to the bolus-fractionation principle. The reproducibility of the method during steady-state conditions was tested in four subjects, and the standard error of measurement was found to be 4%. In four other subjects a visual memory test was given during five of the determinations, and it caused transient flow changes in the occipital regions.

ISSN:0009-7330    

出版商:OVID    

年代:1972

数据来源: OVID