Steroid biosynthesis in turtle testes.

Testicular metabolism of radiolabelled substrates (pregnenolone, progesterone and androstenedione) was examined in two species of turtles, Pseudemys scripta and Sternotherus odoratus. Chemical methods (chromatography, derivative formation and crystallization) identified testosterone (in both species) and 5 alpha-androstane-3 beta,17 beta-diol (in S. odoratus) as products. Tentative identifications were also made of 20 beta-hydroxypregn-4-en-3-one in both turtles. Chromatographic profiles indicated the presence of several other C19- and C21-steroids. In S. odoratus, changes in proportions of the two major C19-compounds (testosterone and the 5 alpha-androstanediol) suggest a "switch" in the enzymatic pathways which resembles that associated with maturation in the rat. This enzymatic switch may be associated with the annual testicular cycle of the adult turtle.