ADRENOCORTICOTROPHIN AND CORTICOSTEROID CHANGES DURING DEXAMETHASONE INFUSION TO INTACT AND SYNACTHEN INFUSION TO HYPOPHYSECTOMIZED FOETUSES

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Abstract
Synacthen [cosyntropin] was infused at 10 .mu.g/h into 4 hypophysectomized fetal sheep. This caused a rise in ACTH to a mean value of 512 pg/ml which remained fairly constant and did not show the large fluctuations seen on infusion into intact fetuses. The Synacthen half-life in the circulation had a mean value of 0.27 min. Hypophysectomy did not necessarily delay the fetal corticosteroid reponse to Synacthen infusion. The corticosteroid concentration achieved had a mean value of about 50 ng/ml which is substantially below that for intact fetuses and in 1 case it was maintained at only 20 ng/ml. Despite this delivery occurred within 5 days. Dexamethasone infusion reduced the plasma ACTH concentration by about 70% and the plasma cortisol concentration by about 60%.