Effects of gonadal steroids on melanocytes in developing hamsters

The effects of chronically administered 5 alpha-dihydrotestosterone and estradiol-17 beta on the dorsal costovertebral spots and scrotal skin of intact and hypophysectomized prepubertal male Syrian hamsters were analyzed morphometrically. The 5 alpha-dihydrotestosterone increased pigmentation (optical density) of costovertebral spots and scrotal skin without altering the percentage of pigmented area in intact animals. Spot size and pigment density also increased significantly in hypophysectomized hamsters, but there was no change in the percentage of pigmented area. The 5 alpha-dihydrotestosterone did not alter the percentage of pigmentation in any area of scrotal skin in hypophysectomized animals. In contrast, estradiol produced a dose-related decrease in the number of scrotal skin melanocytes in intact animals. The androgen-induced increase in pigmentation of costovertebral spot hair follicles was reversed by estradiol, which increased pigmentation around the sebaceous glands. These observations suggest that androgenic stimulation of pigmentation in male hamsters is direct, takes place prior to puberty, is probably tissue specific, and is antagonized by estrogens. The differential response to these steroids of melanocytes adjacent to hair follicles and around the perimeter of sebaceous glands may result from changes in the oxidation state of premelanin, an alteration in melanocyte size and shape, or an actual change in the rate of melanin synthesis.