Kinetics of proliferation and differentiation in the hair follicle and epidermis in neonatally undernourished rats.

Cell population growth kinetics of hair follicle and epidermis were measured in rats undernourished during suckling by increasing the litter size. Animals reared in litters of normal size served as controls. There was a marked atrophy of epidermis and hair follicles, and the thickness and length of the hairs were markedly reduced in the undernourished animals. Autoradiography following pulse labeling with 3H TdR demonstrated prolongation of the cell generation cycle. The G2 and S phases were chiefly affected, whereas the G1 was not altered. The double pulse labeling technique indicated a hold-up in the S phase in the epidermis, although the labeling index was not altered in the undernourished rats. On the basis of available literature, it is porposed that G2 is more energy dependent, whereas protein deficiency affects predominantly the S phase. Unlike the alteration in cell generation cycle, the process of differentiation--measured histochemically and on the basis of rate of migration of 3H-TdR-labeled bulb cells--appeared to be unaffected in undernutrition. However, there was a lag in the movement of cells out of the germinative zone. It is proposed that in undernutrition, cells spend longer time in the germinative zone to complete a critical number of division which may be peculiar to every tissue.