PLASMA CORTICOSTERONE LEVELS DURING PREGNANCY IN THE MOUSE: THE RELATIVE CONTRIBUTIONS OF THE ADRENAL GLANDS AND FOETO-PLACENTAL UNITS

Abstract

SUMMARY Plasma corticosterone levels were measured throughout pregnancy and on the first day post partum in the mouse. During the first half of pregnancy plasma corticosterone levels rose from the non-pregnant value of 2·3 μg/100ml to 15·2 μg/100 ml on day 10. During the second half of pregnancy there was a sharp rise, levels reaching a peak of 138·3 μg/100ml on day 16. Following parturition there was a rapid fall to 18·3 μg/100 ml on the morning of the first day post partum. Adrenalectomy on day 15 resulted in an 80% fall in plasma corticosterone levels indicating that most of the steroid was of adrenal origin. The remaining portion of the corticosterone was found to be of foeto-placental origin, and in the chronically adrenalectomized animal this source was capable of maintaining high blood levels of corticosterone (67 μg/100 ml). The foeto-placental unit also provides the main secretory stimulus to the adrenal gland, but the mechanism by which it does this is not understood.