A Study of the Effect of Ovariectomy, Oestrogen and Progesterone on the Melanocytes and Melanin in the Skin of the Female Guinea-Pig

Abstract

1. The effects of ovariectomy, oestrogen and progesterone on the melanocytes and melanin in the skin of the ear, anterior abdominal wall, areola, and sole of foot have been studied in pure black and pure red guinea-pigs.2. Following ovariectomy the melanin content of the melanocytes was reduced and many of the melanocytes became smaller in size and had shortened dendritic processes. Some melanocytes had a deformed appearance, which varied from a minor irregularity of the cell contour to an advanced degree of cell collapse with fragmentation of the dendritic processes. A significant reduction of the melanocyte count occurred only in the areola, and this was accompanied by a reduction in the amount of free melanin.3. In the ovariectomized animals which received oestrogen the amount of melanin was increased both inside and outside the melanocytes in all the regions. The greatest increase occurred in the areola where it was mainly due to a large increase of free melanin. In the nonsexual skin areas there was a smaller increase of free melanin but a greater increase in melanin within the melanocytes. No statistically significant changes in the counts were produced in any of the skin regions. 4. In the ovariectomized animals which received progesterone the amount and depth of colour of the melanin increased both within and outside the melanocytes and this was most marked in the ear. No statistically significant changes in the counts were produced in any of the skin regions. The general effect produced by progesterone was found to be less than that which occurred after oestrogen.Numerous workers have reported that oestrogens can stimulate melanogenesis in the skin in a wide variety of species. Little work, however, has been done on the influence of progesterone on this process, and it would appear from a review of the literature that the effect of ovariectomy on melanogenesis in animals has never been investigated. Many of the observations on the influence of the female sex hormones on pigment formation have been macroscopic only and microscopical studies have been confined to vertical skin sections. Vertical sections have the disadvantage that accurate melanocyte counts are impossible and that the appearances of the melano¬ cytes cannot be adequately demonstrated. The present paper describes a histochemical investigation into the appearances of the melanocytes in the skin of the female guinea-pig following ovariectomy and administration of oestrogen or proge¬ sterone, using both skin sheets and vertical sections. It 'was hoped to establish

Effect of the Melanocyte Stimulating Hormone of the Pituitary on Melanocytes and Melanin in the Skin of Guinea-Pigs

“…This might have been expected since the results of previous work have shown that removal of the ovaries inhibits melanogenesis and reduces the melanin content of the melanocytes (Bischitz & Snell, 1960), and the presence of oestrogen and small doses of progesterone stimulate melanin production (Bischitz & Snell, 1960;Snell & Bischitz, 19606): thus in the present experiment with spayed animals the melanocytes contained less melanin to start with than normal.…”

“…with those following treatment with oestrogen and progesterone (Bischitz & Snell, 1960). These hormones (especially oestrogen) increased the amount of melanin present both within and outside the melanocytes and when given together, or in the case of oestrogen when given in large doses (Snell & Bischitz, 19606) corrected the irregularity of contour found in some of the melanocytes following ovariectomy.…”

The biological actions of estrogens on skin

“…It has been reported that estrogens do not appear to have a definite effect on the hair color of guinea pigs, suggesting that the two types of melanocytes respond differently to this steroid at least in this species (144). However, it must be noted that the methods of assessment in this study were different to the earlier study on epidermal melanogenesis in the guinea pig by the same group (134). In the epidermis, the morphology of the melanocytes and surrounding keratinocytes was studied, while only the hairs and not the follicular melanocytes were examined in this study.…”

“…A number of studies have shown that epidermal melanocytes are estrogen responsive, although the responses are often contradictory and difficult to interpret. In female guinea pigs, after ovariectomy the melanin content of epidermal melanocytes decreases; many become smaller in size and exhibit shortened dendritic processes (134). Furthermore, ovariectomized animals that were treated with estradiol either locally or systemically showed an increase in melanin both inside and outside the melanocytes in all regions examined.…”

Effects of Gonadal Steroids on Melanocytes in Developing Hamsters

“…These observations contrast with the results of systemic or topical application of estrogens, which produced a complete repression in total CV spot area and pigmentation (8,9). The spot appears unique in this respect, since estrogen apparently increases pigmentation in the epidermis of humans (16,17), guinea pigs (18,19), rats (20), fowl (21), and even hamsters (22). This may result from species differences, choice of steroid, or dose selected.…”