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P. Sourdaine and D. H. Garnier

Seminiferous lobules of dogfish (Scyliorhinus canicula) testis comprise cysts formed by steroidproducing Sertoli cells associated with germ cells at an identical stage of spermatogenesis. These lobules were isolated in four populations corresponding to lobules with spermatogonia (A), spermatocytes (B), early spermatids (C) and late spermatids (D). They were used for steroid radioimmunoassay or incubated with 22a-hydroxycholesterol or with dibutyryl cyclic AMP (dibutyryl cAMP) to measure steroid production. Our results indicate that progesterone was the major steroid in seminiferous lobules at all stages of spermatogenesis except in lobules A. Furthermore, marked changes in the distribution of steroids were observed according to the stage of spermatogenesis; progesterone, 4-androstenedione, testosterone and 17α-hydroxy,20β-dihydroprogesterone concentrations were highest in lobules D, whereas dihydrotestosterone concentrations decreased during spermatogenesis. No significant stage-related change was observed for 3α-diol and 3β-diol. Incubation experiments revealed that the isolated seminiferous lobules at all stages can synthesize steroids from hydroxycholesterol and that lobules D have the highest basal contents of androstenedione and testosterone. Furthermore, when dibutyryl cAMP and 10 μmol hydroxycholesterol l−1 were added together to the cultures, an enhancement of the steroid secretion was observed rather than a change in synthesis. Our results also indicated that the responsiveness of the lobules to dibutyryl cAMP varies according to the stage of spermatogenesis and to the steroid assayed. Overall, this study indicated that germ cells probably markedly influence Sertoli cell steroidogenesis in the adult dogfish testis.