The effect of estradiol on the sebaceous gland of the hamster ear and its antagonism by tamoxifen.

To evaluate the antagonism between estradiol and tamoxifen in the sebaceous gland of the hamster ear, animals were topically treated, and the size of the sebaceous glands was measured by histoplanimetry. The systemic effects were described by determining the estradiol and testosterone plasma levels and within the testes, and the size of the seminal vesicles and the contralateral sebaceous gland. The administration of 0.1 micrograms estradiol resulted in a diminution in the size of the treated glands but left all other parameters unchanged, indicating a purely local effect. A higher dose of estradiol (1 microgram) further decreased the size of the treated glands, but this was combined with a systemic effect, i.e. low plasma testosterone, decrease in testis size and a diminution of the contralateral ear gland. Ten micrograms of estradiol maximally suppressed all of the androgen effects without side effects. The administration of tamoxifen alone also decreased the size of the sebaceous glands without side effects, but it did not affect the production or effects of androgens. When administered in combination with estradiol, it antagonized the effects of this hormone completely. We conclude that tamoxifen inhibits the negative effect of estradiol on sebaceous-gland size. It acts predominantly in a systemic manner, because a metabolisation to monohydroxytamoxifen is necessary.