Failure of estradiol benzoate given after birth to prevent the adrenal glands from shrinking in newborn rats.

Two hr after birth, newborn rats were given a subcutaneous injection of 0.01 mg estradiol benzoate dissolved in 0.05 ml sesame oil. Other siblings were given sesame oil alone. Autopsy was performed on days 1, 2 and 3 after birth. Gravimetric and histologic examinations of the adrenals from these animals and from normal littermate controls were made together with the determination of plasma corticosterone concentrations. In all the three groups of rats, estrogen-treated, oil-treated and non-treated, the weight of the adrenal glands declined with a concomitant decrease in the plasma corticosterone concentrations. The results indicate that estradiol benzoate, when given after birth, does not prevent the neonatal adrenal from shrinking.