THE EFFECT OF ADRENALECTOMY AND ADRENOCORTICAL HORMONES ON THE HAIR GROWTH CYCLE IN THE RABBIT AND RAT

SUMMARY The effect of cortisone and adrenalectomy on the hair regrowth cycle of the rat and rabbit was investigated. It was found that bilateral adrenalectomy had no effect on the rate of regrowth of hair or on the quality of the coat in the rabbit, but there was decreased mitotic activity of the follicles on the 2nd and 7th day of the regrowth cycle and increased mitotic activity of the epidermis on the 7th day of this cycle. In the rat bilateral adrenalectomy, apart from causing a generalized wave of hair growth, which was not observed in the rabbit, had no effect on the hair regrowth cycle. The local application of hydrocortisone had a slight inhibitory action in the early stages of the cycle, but i.m. injection of cortisone produced profound inhibition. In the rabbit doses of 12·5 mg/kg body weight caused suppression of the usual regrowth cycle, but in some animals the outercoat hairs were unaffected. There was depression of the mitotic activity of the epidermis on the 7th and 10th days of the cycle. If cortisone was given during different stages of the regrowth cycle growth of undercoat hair was much more inhibited than that of the outercoat hair. Similar results were observed in the rat. These results are discussed and it is postulated that the difference in response between the two types of hair might be related to differences in blood supply of the outercoat and undercoat hairs.