Physiological Inhibition of Ovine Fetal Plasma Benin Activity by Cortisol*

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Abstract
The hypothesis that physiological increases in the fetal plasma cortisol concentration alter basal and stimulated levels of PRA [plasma renin activity] and vasopressin. Seven fetal sheep, between 121 and 131 days gestation, were infused with cortisol (4 .mu.g/min) or vehicle for 5 h. One hour after the end of cortisol or vehicle infusion, sodium nitroprusside was infused into the fetus (100 .mu.g/min, i.v.) to stimulate fetal hormone secretion. Cortisol, but not vehicle, infusion increased the fetal plasma cortisol concentration and decreased fetal PRA, but did not alter the fetal plasma vasopressin concentration. Cortisol-infused fetuses responded to nitroprusside with slightly smaller PRA responses but with equal vasopressin responses compared to those of vehicle-infused controls. Fetal blood pressure was not affected by either cortisol or vehicle infusion. Nitroprusside caused a slightly greater reduction in pressure in fetuses receiving cortisol infusion compared to those receiving the vehicle. Physiological increases in fetal plasma cortisol decrease fetal PRA without altering the fetal plasma vasopressin concentration. Repeated fetal stress might produce progressive reduction of fetal PRA activity and might, therefore, alter cardiovascular homeostasis.