Adrenocorticotrophin and corticosteroid changes during dexamethasone infusion to intact and synacthen infusion to hypophysectomized foetuses.

Synacthen has been infused at 10 microgram/h into 4 hypophysectomized foetal sheep. This caused a rise in adrenocorticotrophin to a mean value of 512 pg/ml which remained fairly constant and did not show the large fluctuations seen on infusion into intact foetuses. The Synacthen half-life in the circulation had a mean value of 0.27 min. Hypophysectomy did not necessarily delay the foetal corticosteroid response to Synacthen infusion. The corticosteroid concentration achieved had a mean value of about 50 ng/ml which is substantially below that for intact foetuses and in one case it was maintained at only 20 ng/ml. Despite this delivery occurred within 5 days. Dexamethasone infusion reduced the plasma adrenocorticotrophin concentration by about 70% and the plasma cortisol concentration by about 60%.