The placenta secretes large amounts of the hypothalamic releasing hormone, corticotropin-releasing hormone (CRH), into both the maternal and fetal circulation during pregnancy. We characterized the relationship between maternal plasma CRH and products of the pituitary and adrenal in order to investigate the physiologic role of placental CRH in modulating maternal pituitary-adrenal function. Plasma was obtained from 8 women at biweekly intervals between 21 and 40 weeks of full-term pregnancy for CRH, adrenocorticotropin (ACTH), alpha-melanocyte-stimulating hormone (alpha MSH), cortisol, and dehydroepiandrosterone sulfate (DHEAS) measurements by radioimmunoassay. Eighteen women were also studied once at 22-34 weeks of pregnancy with plasma CRH and 24-hour urinary free cortisol measurement. Eight nonpregnant women served as control subjects. Plasma CRH was undetectable in the nonpregnant subjects and rose over the time period studied in the pregnant women. Concentrations of afternoon ACTH and cortisol also rose during pregnancy while DHEAS levels declined in the pregnant women. The alpha-MSH levels were beneath the level of detection (< 20 pg/ml) in both the pregnant and nonpregnant subjects. The overall mean afternoon ACTH concentration was higher in the pregnant than in the nonpregnant women (11.4 +/- 1.8 vs. 5.9 +/- 1.8 pg/ml; p < 0.05), although the ACTH levels in both groups remained within the normal range. The mean plasma cortisol concentrations were higher in the pregnant women, while the mean DHEAS levels were lower in the pregnant women when compared to the nonpregnant subjects.(ABSTRACT TRUNCATED AT 250 WORDS)