Induction of premature parturition in sheep: adrenocorticotrophin and corticosteroid changes during infusion of Synacthen into the foetus.

Synacthen (10 microgram/h) infused into foetal sheep at about day 125 of gestation caused premature delivery within 4 days. During the first 24 h of the infusion the secretion of adrenocorticotrophin was depressed and the assayable hormone concentration was within 500-1000 pg/ml. Subsequently, large fluctuations occurred in the adrenocorticotrophin concentration in the plasma of foetal sheep which were consistent with the stimulation of adrenocorticotrophin secretion. No transfer of Synachthen to non-infused twin foetuses was observed. The plasma corticosteroid concentration in the infused foetus also showed a small rise during the first 24 h of the infusion followed by large fluctuations in concentrations that coincided with the changes in adrenocorticotrophin. No consistent changes in the plasma corticosteroid concentration in the non-infused twin foetus were observed. These results are discussed in relation to the hormone changes occurring during normal delivery.