The effect of rat serum on the morphology of rat hair follicles in tissue culture.

Rat hair follicles obtained from the skin of 12-day-old animals were cultured in the presence of 20% fetal calf serum and compared with those cultured in the presence of 20% rat serum obtained from animals aged 12-14, 18-20 days; and 1 year. Follicles cultured in the presence of fetal calf or 12-14-day rat serum showed no morphological change after 2 days of culture. Follicles cultured in the presence of 18-20 day serum or adult serum for 2 days showed greatly altered morphology, the dermal papilla degenerated, keratinization of hair cells occurred, and an enlarged outer sheath developed. The cells in this sheath contained many filaments which were periodic acid-Schiff positive. These changes are compared with those occurring during the catagen phase of the hair cycle in vivo.