Hormonal control of melanin pigmentation in scrotal skin of the rat

The biological actions of estrogens on skin

There is still extensive disparity in our understanding of how estrogens exert their actions, particularly in non-reproductive tissues such as the skin. Although it has been recognized for some time that estrogens have significant effects on many aspects of skin physiology and pathophysiology, studies on estrogen action in skin have been limited. However, estrogens clearly have an important function in many components of human skin including the epidermis, dermis, vasculature, hair follicle and the sebaceous, eccrine and apocrine glands, having significant roles in skin aging, pigmentation, hair growth, sebum production and skin cancer. The recent discovery of a second intracellular estrogen receptor (ERbeta) with different cell-specific roles to the classic estrogen receptor (ERalpha), and the identification of cell surface estrogen receptors, has provided further challenges to understanding the mechanism of estrogen action. It is now time to readdress many of the outstanding questions regarding the role of estrogens in skin and improve our understanding of the physiology and interaction of steroid hormones and their receptors in human skin. Not only will this lead to a better understanding of estrogen action, but may also provide a basis for further interventions in pathological processes that involve dysregulation of estrogen action.

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.

Ultrastructure of normals and castrates and the effects of testosterone and ultraviolet (UVL-B) irradiation on scrotal skin of rats

The ultrastructure of the testosterone dependent epidermal melanocyte system of the scrotal skin of normals and castrates, with and without testosterone replacement therapy, and UVL-B (280-315 nm) radiation in black Long Evans rats is reported. UVL-B increases melanocyte activity, melanosome forming apparatus, (size of Golgi zone and RER, and quantity of cytoplasmic vesicles, dendrites, and stages of melanosomes) in normals and in castrates. Testosterone replacement therapy to castrates is not a prerequisite for stimulation by UVL-B, but it enhances the effects of UVL-B without restoring normalcy as melanosome packaging into complexes predominates. After UVL-B stimulation of normals or castrates, melanocyte dendrites are observed more often. Melanocyte dendrites of skin of castrated rats are observed less often than in normals, but with testosterone replacement therapy, the dendrites become more numerous. Melanosomes donated to keratinocytes are mostly located as singles in normals and as complexes in castrates. After UVL-B, castration, or testosterone replacement therapy, the melanosomes are packaged in keratinocytes in complexes larger than in normals. In the epidermis of long term castrates (9-109 days), non-specific clear cells are observed and Langerhans cells containing melanosomes; we did not observe them in normals. Melanocytes of castrates have a reduced melanosome forming apparatus. The dermis of castrates contains many dermal melanocytes in the superficial dermis with melanosomes in several stages of formation. These cells are not apparent in normals at this location in the dermis. Testosterone replacement therapy and/or UVL-B administered to castrates does not restore the epidermal melanocyte system nor the dermis to precastration ultrastructural appearance; castration has a permanent altering effect as melanosomes are packaged into complexes.

Testosterone and UVL-B stimulation of epidermal melanocytes in rat scrotal skin

The effects of UVL-B and/or testosterone replacemnt therapy are compared in normal and castrated rats in order to determine whether testosterone is required for UVL-B (290-315 nm) stimulation of melanogenesis in the testosterone-dependent epidermal melanocyte system of the scrotal skin of black Long Evans rats. Testosterone is not a prerequisite for UVL-B stimulation of melanocytes as in both castrates and normal animals the melanocytes respond to UVL-B by increases in size, length and number of dendrites (dendriticness), and tyrosinase activity (intensity of Dopa reaction). Addition of testosterone to castrates does enhance the effects of UVL-B. However, UVL-B with or without testosterone cannot maintain normal melanogenesis in rats irradiated immediately after castration nor can it restore normal melanogenesis following long term castration. Bth the amount of UVL nergy/exposure and the number of exposures are important variables in stimulation of the epidermal melanocytes. Administration of a dose of UVL-B to castrates in a single exposure is ineffective, while the same overall dose spread over several exposures increases the size and dendriticness of melanocytes. Testosterone and UVL-B act synergistically in affecting melanogenesis although neither singly nor in combination are they able to fully restore normal melanogenesis.

Giant pigment granules in dermal melanocytes of rat scrotal skin

Giant melanosomes, ellipsoidal (1.5 micron X 1.3 micron) or spherical (1.1 micron-1.4 micron in diameter) exist in the scrotal skin of the black pelted Long Evans rat. They are longer and wider than normal stage IV melanosomes (0.7 micron X 0.4 micron) found in these dermal melanocytes.

Organ culture of mammalian skin and the effects of ultraviolet light and testosterone on melanocyte morphology and function

Scrotal skin of black Long-Evans rats and human thigh skin were maintained in vitro as organ cultures for as long as 14 days, and examined histologically using the combined skin splitting and Dopa techniques. Selected rat skin cultures received testosterone in the culture medium and/or were irradiated with ultraviolet light (290-320 nm UVL). With increased time in culture, scrotal melanocytes round up and there is an increase in epidermal pigmentation. Human skin behaves similarly; after eight days in vitro human melanocytes also become rounded, but remain strongly Dopa-positive. Addition of exogenous testosterone to cultured rat skin maintains dendritic morphology of melanocytes, but cell body size is still reduced. UVL irradiation stimulates melanocytes in rat skin cultures, maintaining their dendritic morphology and increasing epidermal and dermal pigmentation. Cultured skin receiving both UVL and testosterone illustrates a synergistic effect. Electron microscopic examination of cultured rat skin shows the presence of large melanosome complexes in keratinocytes, much larger than those found in vivo. Melanocytes appear to be active as they contain an extensive Golgi zone, rough endoplasmic reticulum, and melanosomes in various stages of formation. Dermis contained many dermal melanocytes and macrophages laden with melanosomes, correlating with the increased visible dermal pigmentation in vitro. This UVL stimulation of melanocytes in our skin organ cultures contrasts with the lack of melanogenic stimulation found in melanoma cell cultures. Our findings suggest that the intact epidermal melanin unit may be necessary for UVL stimulation of melanocytes.

Effect of ascorbic acid on pigmentation of toad (Bufo melanostictus)

Administration of ascorbic acid in toad during breeding season results an increase in melanin pigments in skin, liver and vocal sac.