摘要:

The role of the vagus in the control of coronary blood flow was studied in chloralose-anesthetized dogs with open chests. Propranolol, 1.0 mg/kg iv, was used for beta-receptor blockade. Heart rate was maintained at a constant level with atrial and ventricular pacing. Left circumflex coronary artery blood flow was measured with an electromagnetic flowmeter. The experimental design accounted for the four major determinants of coronary blood flow: (1) aortic pressure, (2) myocardial systolic compression, (3) alterations in myocardial oxygen tension and metabolism secondary to changes in contractile force, (4) neural control. Efferent stimulation of the cut cervical vagi (30 Hz, 2 msec, 8-10 v) resulted in decreased aortic blood pressure and increased coronary blood flow. Late diastolic coronary artery resistance fell to 58% of the control value after 5 seconds of vagal stimulation. Atropine, 0.5 mg/kg iv, blocked these effects. It is concluded that direct parasympathetic coronary vasodilation results from vagal stimulation, which is independent of vagal chronotropic and inotropic effects.

ISSN:0009-7330    

出版商:OVID    

年代:1969

数据来源: OVID

ISSN:0009-7330    

出版商:OVID    

年代:1969

数据来源: OVID

摘要:

Previous studies showed that synthetic bradykinin produced in-vitro constriction of the ductus arteriosus of the fetal lamb and guinea pig, constriction of isolated human and lamb umbilical vessels, and pulmonary vasodilatation in the fetal lamb.The present study showed that bradykinin precursor, kininogen, is present in arterial blood of the fetal lamb by 61 days of gestation and that its concentration increases toward term. We studied the bradykinin-generating system in 6 exteriorized fetal lambs. Kininogen concentrations in left atrial blood decreased within 1 to 2 minutes after beginning ventilation with O2, and free bradykinin was detected in left atrial blood. Pulmonary arterial blood kininogen concentration was not significantly altered. Kininogen concentration in left atrial blood did not fall in 4 other lambs ventilated with N2but did fall after subsequent ventilation with O2. To study the effects of increased oxygenation in utero without lung expansion, 6 pregnant ewes were exposed to hyperbaric O2at 3.63 atmospheres absolute. Associated with a mean increase in brachial arterial blood Po2to 44 mm Hg, a value equivalent to that in the ventilated exteriorized fetus, kininogen concentration fell, and free bradykinin was detected in the brachial arterial blood of 3 of the 6 fetuses. In 4 other exteriorized lambs we measured kininogen concentration in brachial arterial and right ventricular blood at frequent intervals up to 30 minutes after ventilation with O2. The concentration in brachial arterial blood fell before that in right ventricular blood.The hypothesis is presented diat bradykinin is produced from kininogen in the lungs of the fetal lamb when oxygenated, and that the maximal rate of production occurs during the first few minutes after expansion of the lungs or exposure of the ewe and fetus to hyperbaric O2.

ISSN:0009-7330    

出版商:OVID    

年代:1969

数据来源: OVID

摘要:

The degeneration of acetylcholinesterase-positive nerve fibers in 11 canine renal autotransplants was investigated with the thiocholine method of Karnovsky and Roots as modified for cryostat sections. Seven renal hila were also examined by silver impregnation and thiocholine techniques. Total denervation was demonstrated in only 3 of 11 autotransplants; the other 8 showed variable degrees of degeneration, from almost total to very little. Acetylcholinesterasepositive nerve fibers accompanied the renal, interlobar, arcuate, and interlobular arteries and the afferent arterioles and vasa recta. Acetylcholinesterase activity was apparent in glomeruli but was greatly diminished or abolished by renal perfusion with normal saline before histologic procedures were begun. Discrete autonomic ganglia were seen in the renal hila. We believe these acetylcholinesterase-positive ganglion cells (also found scattered along hilar nerve bundles) are the source of the nerve fibers which remain intact and viable following vascular division during transplantation.

ISSN:0009-7330    

出版商:OVID    

年代:1969

数据来源: OVID

ISSN:0009-7330    

出版商:OVID    

年代:1969

数据来源: OVID

摘要:

The effect of methyldopa on plasma renin activity was studied in one hypertensive and four normotensive human volunteers. Peripheral venous blood for the estimation of plasma renin activity was obtained with the subjects supine and in a 70° head-up tilted position before, during and, in two subjects, after treatment with oral methyldopa. Despite a reduction in mean arterial pressure, the plasma renin activity was decreased by methyldopa in each subject. The increase in plasma renin activity associated with tilting, however, was not significantly suppressed by methyldopa. These results indicate that treatment with methyldopa can simultaneously decrease mean arterial pressure and plasma renin activity and it is possible that these effects may be causally related.

ISSN:0009-7330    

出版商:OVID    

年代:1969

数据来源: OVID

摘要:

In situ studies yield only indirect evidence as to whether non-neurogenic vascular tone results from an intrinsic myogenic tendency of the smooth muscle cell to contract or is due to stimulation of the muscle by some vasoactive humoral influence of the environment. In the current study, small resistance vessels from different vascular beds, from various levels of the arterial tree, and from several species were isolated and perfused with physiological salt solution. Under these conditions the environment is devoid of any vasoactive, in-situ, humoral influence, and tonic contraction would have to be of myogenic origin. Myogenic tone was consistently present in smooth muscle from some vascular beds, whereas it was absent from other beds. Myogenic tone was more prevalent in smaller vessels (50 to 100μ o.d.) than in larger ones (100 to 400μ o.d.). Significant differences in this property were observed among the species studied. We conclude that, contrary to the properties classically assigned it as a multiunit smooth muscle, most vascular smooth muscle from resistance vessels is intrinsically and spontaneously active.

ISSN:0009-7330    

出版商:OVID    

年代:1969

数据来源: OVID

ISSN:0009-7330    

出版商:OVID    

年代:1969

数据来源: OVID

摘要:

Ventricular function curves of cardiac output and stroke volume versus left ventricular end-diastolic pressure were obtained during rapid infusion of Tyrode's solution in dogs standing at rest and during near-maximal exercise both before and after administration of propranolol. Cardiac output and stroke volume ventricular function curves were expressions of first-order processes as indicated by the close fit of data points to computer-derived exponential curves. At near-maximal levels of exercise, the rapid infusion of Tyrode's solution increased stroke volume by an average of 12 ml, indicating that at near-maximal exercise the pumping ability of the heart may be limited by venous return rather than by ventricular performance. The heightened sympathetic activity during exercise increased myocardial contractility, since the plateaus of the ventricular function curves were significantly higher during exercise than at rest. Propranolol negated the increase in contractility associated with exercise and the plateaus of ventricular function curves were then not significantly different from those obtained at rest.

ISSN:0009-7330    

出版商:OVID    

年代:1969

数据来源: OVID

ISSN:0009-7330    

出版商:OVID    

年代:1969

数据来源: OVID