THE EFFECTS OF ANTIDIURETIC HORMONE ON URINE FLOW AND COMPOSITION IN THE CHRONICALLY-CANNULATED OVINE FETUS

Abstract
The fetuses of 9 pregnant ewes were chronically cannulated between 86 and 130 days with cannulae in 1 carotid artery, 1 jugular vein, the fetal bladder and the amniotic cavity. The effects of infused AVP [arginine vasopressin] on fetal urine flow rate and composition were studied. A dose of 35 pmol/h always caused an increase in urine osmolality and a decrease in flow rate and free water clearance without change in blood pressure. Higher doses (140 pmol/h) were significantly pressor and caused increased excretion of Na, Cl, urea and creatinine. Although this dose always caused an increase in urine osmolality, in 5 experiments the flow rate also rose. The ovine fetus apparently has the ability to control its own urine flow and composition, and possibly also amniotic fluid volume and composition.

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