The peripartal endocrine system in sheep

Abstract

In vitro studies with isolated fetal adrenal cells have demonstrated their responsiveness to ACTH at day 50 p.c., their desensitization by day 100, and re-emergence of the response pattern between day 135 and term. Fetal adrenal cells at day 130 p.c. did not produce cortisol after addition of amounts of dbcAMP which stimulated maternal adrenals to secrete the steroid. The ability of fetal adrenal cells to respond either to ACTH or during co-culture with fetal pituitary cells was influenced by their method of preparation. Harsher dispersion with collagenase increased their response, whereas digestion with trypsin inhibited it. Term fetal adrenals produced cortisol in response to ACTH and αMSH. However, when αMSH was added together with ACTH, the ACTH-induced response was reduced. In vivo experiments showed that fetal plasma cortisol concentrations varied in a pulsatile manner. In late pregnancy cortisol in fetal plasma and amniotic fluid were correlated. Before parturition, there was a progressive rise in the amniotic fluid concentration of progesterone, and a sharp increase in amniotic fluid estrone. These results are discussed in relation to the central role of the fetal adrenal, its possible desensitization and reactivation, and the importance of amniotic fluid steroids in the process of parturition.