The sinus hair follicle of the cat. Hair growth and hair cycle.

The cat's sinus hair follicle is described histologically with special regard to structural characteristics and functional mechanisms of sinus hair growth and sinus hair cycle. Special features of both cornification of the inner epithelial root sheath and hair fixation, respectively, result in a loss of traction that is required for hair growth and hair expulsion. Instead, there is the outgrowing new anagen sinus hair that pushes the preceeding sinus hair upwards, and - secondly - there is a long-lasting cell pro- liferation. Cell proliferation - immunocytochemically detected with anti-proliferating cell nuclear antigen - continues in the preceeding sinus hair while the formation of a new, succeeding sinus hair follicle begins. No distinct, 'typical' catagen state of sinus hair follicle has been found even in a large number of collected specimens. These findings stress that the well known features of hair growth and hair cycle in the pelage hair follicle cannot be generalized and adopted in all details to the sinus hair follicle. Copyright 2000 S. Karger AG, Basel