Antidiuretic Hormone and Oxytocin Release and Antidiuretic Hormone Turnover in the Fetus, Lamb and Ewe

Abstract

The release of antidiuretic hormone in response to the introduction of an osmotic stimulus into the cerebral circulation of the fetal sheep and lamb is described. Infusion of 1.0 M sodium chloride solution (mean 0.22 ml/kg/min, range 0.15–0.42 ml/kg/min) into the carotid artery of the acutely exteriorised fetus led to a rise in fetal plasma arginine vasopressin (AVP) concentration within 5 min. The response was independent of age in the range 113–138 days gestation age. No clear-cut response was obtained in the lamb. In some of the fetal experiments infusion of 0.1 M calcium chloride solution into the carotid artery (mean 0.54 ml/kg/min, range 0.34–0.84 ml/kg/min) led within 2 min to the release of appreciable quantities of both AVP and oxytocin. Turnover measurements of bioassayable AVP indicate a significantly shorter half-life of this hormone in the fetal circulation (3.7 ± 0.7 min, mean ± SEM) when compared with the mother (5.9 ± 0.48 min, mean ± SEM) with an intermediate value in the lamb.

Regulation of Urine Osmolality in Fetal Sheep

“…However, the fetal kidney did show increasing responsiveness to infused AVP as the minimum plasma ADH concentration which had to be established to produce these results decreasing with increasing gestational age, being 22 1, 1 1 1 and 7 0 pg/ml at 105, 115 and 125 d respectively. The blood clearance rate of AVP was not correlated with fetal age as found by Robillard & Weitzman (1980) and was in the same range as previously reported (Alexander, Bashore Britton & Forsling, 1976;Iwamoto et al 1978;Rurak, 1978;Robillard & Weitzman, 1980). The increasing responsiveness of the fetal kidney to infused AVP may be due to an age-dependent increase in numbers of ADH receptors, or an increase of adenylate cyclase activation, but no experiments on ovine fetal kidneys have been done to examine these propositions.…”

Hemodynamic responses of the sheep fetus to vasopressin infusion.

“…The cardiovascular system of the fetus responds to neurohypophysial hormones; intravenous infusion of arginine vasopressin into the sheep fetus has been shown to cause an increase in blood pressure and a decrease in heart rate (Rurak, 1975;Alexander et al, 1976). At present there is no information regarding the specific actions of arginine vasopressin on the cardiovascular system of the fetus.…”

“…It is not known, however, whether arginine vasopressin has a role in normal fetal physiology or in the fetal response to stressful stimuli. Plasma concentrations of arginine vasopressin in the sheep fetus have been shown to be elevated in response to various stimuli such as fetal hemorrhage, hypoxia, increased plasma sodium, and surgical manipulation (Alexander et al, 1974a, b;Rurak, 1975;Skowsky et al, 1973;Alexander et al, 1972).The cardiovascular system of the fetus responds to neurohypophysial hormones; intravenous infusion of arginine vasopressin into the sheep fetus has been shown to cause an increase in blood pressure and a decrease in heart rate (Rurak, 1975;Alexander et al, 1976). At present there is no information regarding the specific actions of arginine vasopressin on the cardiovascular system of the fetus.…”

Plasma vasopressin levels during hypoxaemia and the cardiovascular effects of exogenous vasopressin in foetal and adult sheep.

“…(Alexander et al 1976;Stark et al 1977;Leake et al 1977). These concentrations are similar to those found in the ewe and in other adult mammals.…”