EFFECTS OF INSULIN AND INSULIN-LIKE GROWTH-FACTORS ON CULTURED HUMAN HAIR-FOLLICLES - IGF-I AT PHYSIOLOGICAL CONCENTRATIONS IS AN IMPORTANTREGULATOR OF HAIR FOLLICLE GROWTH IN-VITRO

Insulin stimulated hair follicle growth in a dose-dependent manner ove r the range of 0.01 to 100 mu g/ml. Maximum rates of hair follicle gro wth were observed when follicles were maintained in medium containing 10 mu g/ml insulin, which is supraphysiologic. Hair follicles maintain ed in the absence of insulin or at physiologic levels showed premature entry into a catagen-like state. Insulin-like growth factor (IGF)-I a nd -II had no significant effect on hair follicle growth when maintain ed in the presence of 10 mu g/ml insulin. However, in the absence of i nsulin, both IGF-I(0.01-100 ng/ml) and IGF-II (0.01-100 ng/ml) stimula ted hair follicle growth in a dose-dependent manner. IGF-I was more po tent than either insulin or IGF-II, stimulating maximum rates of hair follicle growth at 10 ng/ml, whereas IGF-II gave maximum stimulation a t 100 ng/ml. The rates of hair follicle growth stimulated by 10 ng/ml IGF-I were identical to those stimulated by 10 mu g/ml insulin. IGF-II (100 ng/ml), however, was unable to stimulate hair follicle growth to the same extent as insulin. Both IGF-I (10 ng/ml) and IGF-II(100 ng/m l) were more potent than insulin at preventing hair follicles from ent ering into a catagen-like state. Growth hormone had no effect on hair follicle growth or morphology in the absence of insulin. These data su ggest that in vitro IGF-I may be an important physiologic regulator of hair growth and possibly the hair growth cycle. Moreover, the removal of insulin from tissue culture medium may be a useful method of gener ating large numbers of catagen hair follicles for further in vitro stu dies.