PIGMENTATION AND HAIR GROWTH IN BLACK RATS, AS MODIFIED BY THE CHRONIC ADMINISTRATION OF THIOUREA, PHENYL THIOUREA AND ALPHA-NAPHTHYL THIOUREA1

Abstract

A study has been made of the normal progressive changes in skin pigmentation and in hair growth and color of black rats, brown wild Norway rats, and black mice, and of how these normal patterns are affected in black rats by the chronic admn. of thiourea, phenyl thiourea and a-naphthyl thiourea. The observations of other workers as to the normal rhythmic production of visible skin pigment in sharply defined areas of skin, followed by growth of hair only where the pigment has appeared, have been confirmed and extended, and a description given of how the stages of follicular activity can be deduced from the gross appearance of the skin. Thiourea had no significant effect on the hair growth cycles, at avg. daily intakes as high as 200 mg./kg. body wt., and no effect on the color of the hair or skin. Phenyl thiourea at avg. daily levels of 25 rag./ kg. or higher did not affect hair growth but inhibited pigment formation for as long as it was administered, thereby causing greying of the hair. When the avg. daily intake of a-naphthyl thiourea amounted to 25 mg./kg. or more, hair growth was almost completely inhibited and the skin remained unpigmented. Withdrawal of both phenyl and alpha-naphthyl thiourea resulted in the rapid reversal of these effects.