PITUITARY-ADRENAL-FUNCTION IN THE IMMATURE OVINE FETUS

Pituitary-adrenal responses to intravenous infusion of ovine corticotr ophin-releasing hormone (oCRH) or arginine vasopressin (AW) and to hae morrhage were examined in the ovine foetus prior to 90 days of gestati on (term 145-150 days). In chronically cannulated foetuses (n=8), betw een 74 and 84 days of gestation, basal ACTH levels were less than 20 p g/ml while cortisol levels were 6.5 +/- 1.5 nmol/l (mean +/- S.E.M.). Intravenous infusion of oCRH (1 mu g/h for 60 min) or AVP (1 mu g/h fo r 60 min) significantly increased ACTH (P<0.05 for both treatments) an d cortisol (P<0.01 for both treatments) levels, although the response to both hormones was modest. In acutely studied foetuses of a similar age (70-90 days of gestation, mean 82.0 +/- 1.4 days, n=7), exterioriz ation and progressive haemorrhage significantly (P<0.05) elevated ACTH levels from 117.4 +/- 32.1 pg/ml to a maximal value of 329.2 +/- 112. 8 pg/ml, the maximal ACTH response corresponding to the removal of a v olume of blood equivalent to 6.6 +/- 1.2% of the pre-haemorrhage body weight. The present study has demonstrated that the ovine foetal pitui tary, in vivo, is responsive to exogenous and endogenous stimuli by mi d-gestation and, at this age, although basal cortisol levels are low, the foetal adrenal is capable of responding to elevated ACTH levels in the short term.