PERINATAL REGULATION OF CORTISOL IN THE PRIMATE

Abstract

These studies were designed to assess regulation of steroidogenic function of the human and rhesus monkey fetal adrenal gland. Studies were performed in vitro using superfusion and, in the monkey, in vivo, using fetal monkeys bearing catheters chronically implanted in utero. In vitro, there is functional specialization of the fetal and definitive zones of the human and monkey fetal adrenal glands. The definitive zone produces cortisol stimulable by ACTH and the fetal zone produces principally dehydroepiandrosterone sulfate which also can be stimulated by ACTH. In vivo, an increase in cortisol was seen in the fetal circulation toward the end of gestation. Administration of dexamethasone caused a prompt reduction in fetal cortisol and ACTH, indicating integrity of the fetal pituitary-adrenal axis. When fetal monkeys were challenged with 0.5 i.u. of ACTH only three of the nine studied had a cortisol response. In contrast, newborns delivered by hysterotomy and those delivered vaginally following labor all responded to ACTH stimulation. The responses of the newborns delivered vaginally after labor were greater than in the group delivered by hysterotomy prior to labor. The fetal metabolic clearance rate (MCR), production rate (PR), secretion rate (SR) and placental transfer of cortisol were determined in utero. The MCR of cortisol in the fetus was markedly greater than in the newborn which, in turn, was greater than in the adult. The PR of cortisol was higher in the fetus than in the mother when expressed on the basis of body weight. The difference between PR and SR in the fetus is due to transplacental passage of cortisol from the mother. Expressed on the basis of body weight, SR's in fetus and mother were not significantly different. There is an increase in fetal cortisol SR toward the end of pregnancy and immediately prior to or during labor which may play a role in parturition.