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Uptake in vivo of (3-H) testosterone by the interstitial compartment in testes of normal adult mice.

Although it is generally agreed that the Leydig cells are the predominant site of biosynthesis of testosterone, it has been suggested that androgen action upon these cells may be required for the maintenance of their steroid synthesizing enzymes (Blackburn, Chung, Bullock & Bardin, 1973). Parvinen, Hurme & Niem (1970) have shown that labelled testosterone, pregnenolone and progesterone administered intravenously can penetrate into the seminiferous tubules of rats within 2 to 5 min, but the radioactivity in the tubules was always significantly lower than in the interstitial tissue. Van Doorn, de Bruyn, Galjaard & van der Molen (1974) noted that [3H]testosterone administered intravenously with Krebs-Ringer bicarbonate solution resulted primarily in interstitial localization for periods up to 1 hr in rabbits, but the delayed penetration into the tubules was not seen when the androgen was administered with blood as a medium. They concluded that androgens can pass from Leydig cells into the seminiferous epithelium and suggested that plasma proteins may influence the transport and uptake of these steroids by the tubules. In rabbits and rats, respectively, Galjaard, van Gaasbeek, de Bruyn & van der Molen (1970) and Cooke, De Jong, van der Molen & Rommerts (1970) have also demonstrated that androgens can pass from the interstitial compartment into the epithelium of the seminiferous tubules. Investigations concerning androgen biosynthesis and the effect of androgens on the testis have been carried out predominantly on the individual (tubular