Effect of the melanocyte stimulating hormone of the pituitary on melanocytes and melanin in the skin of guinea-pigs

1. The effect of beta melanocyte stimulating hormone (β-m.s.h.) extracted from the posterior pituitary of the hog, on the melanocytes and melanin in the skin of the ear, anterior abdominal wall, areola and sole of foot has been studied in pure black and pure red intact male and ovariectomized female guinea-pigs. The hormone was injected subcutaneously twice daily 5 days/week for 1 month.

2. Apart from a slight increase in the pigmentation of the skin of the anterior abdominal wall and areola of one male guinea-pig, no obvious changes were noted microscopically.

3. Histological investigation showed that the hormone caused an increase in the length, width and complexity of the dendritic processes and that this was accompanied by an increase in the amount of melanin present within the processes. In the skin of the anterior abdominal wall numbers of melanocytes were significantly raised and the amount of free melanin was increased. In many of the animals the amount of melanin present within the cell bodies of the melanocytes was increased in all the skin regions and in some of these this was associated with an increase in size of the cell body.

4. The hormone produced its greatest effect on the melanocytes in males.

THE ADIPOKINETIC ACTIVITIES OF THE CORTICOTROPHINS AND MELANOCYTE STIMULATING HORMONES

Pepsin degraded and non-degraded corticotrophin (ACTH) preparations all are highly adipokinetic and, in general, this parallels ACTH activity. a and β melanocyte stimulating hormones (MSH) are largely devoid of this activity. The structures necessary for fat mobilizing activity are similar but not identical to those for ACTH.