On day 20 of gestation, foetal rats received a subcutaneous injection of 0·01 mg oestradiol benzoate dissolved in 0·05 ml sesame oil; foetuses in other litters were given sesame oil alone. Autopsy was performed on day 22 of gestation, at delivery or at various times after birth. Gravimetric and histological observations of the adrenals from oestradiol-treated, oil-treated and intact litter-mate control foetal and neonatal rats were performed together with determination of plasma corticosterone concentrations. Activity of 3β-ol dehydrogenase was also examined histochemically in the adrenals from these animals.
The results indicated that oestradiol benzoate when given prenatally prevented the neonatal decline of adrenal weight and adrenocortical cell size. In normal or oil-treated rats, plasma corticosterone concentration was greatly increased during delivery and 2 h after birth, declining up to 12 h after birth. Oestradiol benzoate prevented this perinatal increase and suppressed the activity of 3β-ol dehydrogenase in the perinatal adrenal cortices.