ABSTRACT
Retinoic acid synthesis in mammalian testes illustrates the importance of generating retinoic acid in situ. Because exogenous retinoic acid does not support vitamin A-dependent functions in mammalian testes, historically it has not been viewed as essential for normal reproduction in mammalian males. But mammalian testes express retinoic acid receptors (37,38) and relatively high concentrations of CRABP (39). Exogenously dosed retinoic acid supports the function of avian testes ( 40), suggesting that retinoic acid cannot cross the distinct mammalian blood-testes barrier, formed by Sertoli cells, and must be generated from retinol in situ in the Sertoli cell or in the adluminal compartment rather than in the interstitium" Sertoli ceUs prepared from 20-day-old male Wistar rats convert retinol into retinoic acid in a concentrationdependent manner. A physiological concentration of retinol (5 J!M) provides retinoic acid synthesis at 24 pmol/hr/plate (J. L. Napoli, unpublished data). These cumulative data indicate that mammalian testes depend on retinoic acid generated in situ.
