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

No abstract

No abstract