The Concentrations of Adrenocorticotrophin, Vasopressin and Oxytocin in the Foetal and Maternal Plasma of the Sheep in the Latter Half of Gestation

Pregnant ewes bearing foetuses aged 80–143 days were anaesthetized by the spinal administration of procaine. The foetus was exteriorized by Caesarian section and amniotic and allantoic fluid samples were removed. Heparinized blood samples were obtained simultaneously from the mother (dorsalis pedis artery) and foetus (umbilical artery) within 15 min of inducing spinal anaesthesia. Plasma was separated immediately at 4 ° and stored at −15 °C. Adrenocorticotrophin (ACTH) was determined by radioimmunoassay (Landon & Greenwood, 1968) after preliminary extraction (Ratcliffe & Edwards, 1970). Antidiuretic activity was assayed as described by Forsling, Jones & Lee (1968). The active material in selected plasma samples was identified as arginine vasopressin (AVP) by its lability to thioglycollate (Ames, Moore & van Dyke, 1950) and tyrosinase (Bisset, 1962), and by radioimmunoassay for AVP (Edwards, Chard, Kitau & Forsling, 1970). Oxytocin was determined by radioimmunoassay (Chard, Boyd, Forsling, McNeilly & Landon, 1970); the foetal fluids were extracted