041 PRELIMINARY STUDIES OF EXOGEN, THE SHEDDING PHASE, OF THE MOUSE HAIR CYCLE.

Kurt Stenn, Yoram Milner, Menas Kizoulis Juvenir Biosciences, Skillman, NJ USA

At the end of the normal hair cycle the hair fiber sheds. This step was recognized, e.g. as animal molting, long before the phases of the cycle were otherwise defined. In the past the shedding process has been thought to be a part of the telogen phase. In view of the trichostatic follicles in animals and, incidentally, in humans, in fact every telogen phase is not associated with hair shedding. Hair shedding then occurs separate from the telogen phase. The latter prompted us to consider that the shedding process is indeed a separate phase of the hair cycle and we refer to it as exogen. We have recently established methods for quantitatively collecting and quantifying shed hair. These methods have allowed us to study shedding in the mouse. We found that exogen is closely coupled to anagen and that the shed hair base differs morphologically from telogen. We postulate that exogen occurs in two steps – an initiator step and a proteolytic effector step.