Hormonal control of melanin pigmentation in scrotal skin of the rat

Abstract

Investigations were undertaken to determine the response of the epidermal melanocytes of black rat scrotal skin to castration and to subcutaneous administration of various steroid and peptide hormones. The resulting changes in cell numbers were determined by direct cell count in unstained whole-skin preparations. A 14-day period of castration resulted in a highly significant decrease in the number of scrotal melanocytes. Extending this period to 28, 42, and 70 days failed to reduce further the cell numbers. Treatment of castrated rats with testosterone propionate increased cell numbers approximately to normal levels while treatment with MSH, ACTH, prolactin, progesterone, and estradiol failed to influence castrate levels. The testosterone effect on scrotal skin melanocytes was not significantly altered by concurrent cortisol administration or by adrenalectomy; hypophysectomy resulted in a significant decrease in cell numbers which could be reversed by testosterone treatment. The number of scrotal melanocytes in intact, untreated animals was found to increase progressively with age. It is concluded that the melanocyte population of the scrotum of the black rat is controlled directly and perhaps exclusively by androgenic hormones. The results are discussed in relation to published studies on hormonally-controlled pigment changes in other mammalian systems.