Inhibition of Estradiol-Induced Pituitary Hypertrophy in Rats. ∗

Summary

Equi-potent doses of estradiol caused greater pituitary enlargement in rats than stilbestrol. A third estrogen, TACE, caused no enlargement whatsoever. When two estrogens were given concurrently there was a competitive, rather than an additive, action. Hence, with each combination the average pituitary weight was between averages obtained when each substance was administered individually. With all estrogens there was evidence for ACTH-stimulated adrenal hyperactivity, determined by increase in adrenal weight and thymus gland involution. The observations that (1) TACE causes adrenal stimulation without pituitary enlargement and (2) combinations of estrogens can bring about an inhibition of the usual pituitary enlargement without a corresponding inhibition of adrenal stimulation suggest that the estrogen-induced hyper-production of ACTH does not depend upon pituitary hypertrophy.