R. Rudelstorfer

Circulatory and renal effects of β-adrenergic-receptor stimulation in pregnant sheep

The effects of beta-adrenergic-receptor stimulation with ritodrine on systemic and pulmonary hemodynamics and on renal handling of water and electrolytes were studied in unanesthetized, chronically instrumented pregnant sheep. Each animal was studied during control, ritodrine, and recovery periods, each lasting 60 minutes, with the use of three different modes of hydration. beta-receptor stimulation produced a significant increase in heart rate and cardiac output and a decrease in systemic vascular resistance. Pulmonary arterial and wedge pressures tended to increase. These circulatory effects were similar for the three types of hydration and they persisted after cessation of infusion. In terms of its renal effects, beta-receptor stimulation elicited a profound decrease in urine flow and in the excretions of sodium and potassium, irrespective of the mode of hydration. The antidiuresis and antinatriuresis were accompanied by no changes in plasma osmolality and sodium concentration, whereas plasma potassium levels decreased. All of these effects persisted for 60 minutes after the cessation of infusion. In the water-loaded experiments, the antidiuresis seemed to be related to increased antidiuretic hormone secretion; in the saline-loaded experiments, however, both the antidiuresis and antinatriuresis appeared to be related to increased renal reabsorption. The changes in renal hemodynamics seemed to have an insignificant role. The amount of fluid retained in the body was greater when ritodrine was infused with saline solution than with dextrose solution. These cardiovascular and renal studies suggest that a circulatory overload may be the major factor in the pathogenesis of pulmonary edema observed during beta-adrenergic-receptor stimulation.

Circulatory responses to hypovolemia in the pregnant and nonpregnant sheep after pharmacologic sympathectomy

Circulatory responses to progressive hypovolemia, hypotensive shock, blood reinfusion, and recovery were studied in pregnant and nonpregnant sheep with an intact or pharmacologically ablated sympathetic nervous system produced by administration of 6-hydroxydopamine. These studies also provided an opportunity to assess the contribution of the sympathetic nervous system to the maintenance of vasomotor tone in the pregnant animal at rest. The results show the following: (1) Although there were some differences in the circulatory adjustments to the initial period of blood loss between intact and sympathectomized animals, the overall circulatory responses to progressive hypovolemia, shock, blood reinfusion, and recovery were not significantly different in animals with intact or ablated sympathetic nervous systems whether or not they were pregnant. (2) The reasons for the similarity of cardiovascular responses to hypovolemia are the marked increase in catecholamine outputs by the adrenal medulla, which was not affected by 6-hydroxydopamine, and the supersensitivity of the systemic vascular beds of the sympathectomized animal to catecholamines. (3) The contribution of the sympathetic nervous system to the maintenance of the resting vasomotor tone is considerably enhanced during pregnancy, as demonstrated by the chronic effects of adrenergic ablation on the resting arterial pressure. (4) The circulation of the pregnant uterus possesses the ability of autoregulation during chronic changes of perfusing pressure as demonstrated by the differences in the arterial pressure and uteroplacental vascular resistance between intact and sympathectomized animals.

Heat flux and oxygen consumption of the pregnant uterus.

Heat flux (conductive and convective heat) and oxygen consumption of the pregnant uterus and its content were measured simultaneously in the same group of pregnant ewes during the acute postoperative period, during a chronic resting period, and during alpha- and beta-adrenergic-receptor stimulation with norepinephrine and ritodrine. Results indicated four conclusions. First, an excellent correlation existed between heat flux and oxygen consumption in the acute and chronic resting condition as well as during increasing uteroplacental vascular resistance and decreasing blood flow produced by norepinephrine infusion; the correlation was not as good during ritodrine infusion. Second, during rest, about 85% of heat generated by the pregnant uterus is eliminated through the uteroplacental circulation while the remaining heat diffuses through the myometrium. Third, during decreasing uteroplacental blood flow and elevated resistance, the pregnant uterus is able to maintain a normal thermostasis by widening the temperature difference in the blood entering and leaving the uterus and by increasing the myometrial heat exchange; oxygen consumption also is maintained at normal level through increase in oxygen extraction. Fourth, with the exception of uteroplacental circulation, the circulatory, metabolic, and thermal conditions of the pregnant ewe are not different after 5 hours from 5 to 7 days after the surgical procedure.

Experimental hypertension in pregnant sheep: III. Central hemodynamic alterations in the one-kidney model

Experimental renal hypertension, with use of the one-kidney, one-clip model, was produced in nine pregnant ewes who were then studied during the last one third of gestation. The animals were chronically instrumented for the recording of arterial pressure, heart rate, and cardiac output; blood volume was determined weekly. The studies were carried out in four phases; a control period of 2 weeks, a surgery period of 1 week, a constriction or hypertensive period, and a postpartum period of 2 weeks. We detected no significant changes in heart rate or cardiac output during any phase of the study. The arterial pressure significantly increased during the constriction and postpartum phases (p less than 0.05). Blood volume remained relatively stable during the three pregnancy phases but significantly decreased in the postpartum phase (p less than 0.05). Systemic vascular resistance followed a pattern similar to that of the arterial pressure.

Experimental hypertension in pregnant sheep

Abstract Experimental renal hypertension, with use of the one-kidney, one-clip model, was produced in nine pregnant ewes who were then studied during the last one third of gestation. The animals were chronically instrumented for the recording of arterial pressure, heart rate, and cardiac output; blood volume was determined weekly. The studies were carried out in four phases; a control period of 2 weeks, a surgery period of 1 week, a constriction or hypertensive period, and a postpartum period of 2 weeks. We detected no significant changes in heart rate or cardiac output during any phase of the study. The arterial pressure significantly increased during the constriction and postpartum phases (p