Functioning of the Pituitary-Adrenocortical Axis in Rats at and After Birth

Abstract

The adrenal ascorbic acid concentration in fetal rats was about 400 mg/100 g the day before parturition. At birth it fell to about 350, returned to 400 on days 1 and 2 postnatally, and then fell precipitously to 210 on day 3, from which low point it rose slowly in 10 days to 310 mg/100 g. During this time, depletion of the adrenal ascorbic acid concentration due to stress occurred the last day prenatally and not again until the 4th day postnatally. In the same rats the plasma concentration of corticosterone was 21 μg/100 ml on the last prenatal day and at birth. It fell slightly to 18 μg/100 ml on postnatal days 1, 2 and 3, and to 10 μg on day 4, where it remained. Stress produced significant increases of the corticosterone concentration in plasma on the last prenatal day, at birth, and not again until the 4th postnatal day. Corticosterone concentration in plasma in the mother was twice that in the fetuses (40 μg and 21 μg/100 ml). Adrenalectomy of the mother reduced her plasma concentration of corticosterone in 12 hr to that of the fetuses. After delivery, the corticosterone concentration in the adrenalectomized mother’s plasma fell to less than 10 μg/100 ml, but it remained on the same level in the plasma of the newborn rats (30.5 μg and 26 μg/100 ml). Injection of epinephrine into newborn rats immediately after birth did not deplete the adrenal ascorbic acid concentration in newborn rats of the 3-hr previously adrenalectomized or normal mothers. Under the same conditions, a significant adrenal ascorbic acid depletion occurred if the pregnant rats were adrenalectomized 24–36 hr before delivery.