The adult dogfish (Scyliorhinus canicula L.) testis: a model to study stage-dependent changes in steroid levels during spermatogenesis.

The unit structure of the testis of Scyliorhinus canicula L. is the seminiferous lobule arranged in topographically distinct zones and comprised of cysts formed by steroid-producing Sertoli cells associated with germ cells at an identical stage of spermatogenesis. In this experiment, testicular tissues from different dogfish corresponding to the zones of lobules with spermatogonia (A), spermatocytes (B), early spermatids (C) and late spermatids (D) were dissected out and pooled. They were either used for steroid radioimmunoassay or incubated to measure steroid production in response to dogfish pituitary extract or to dibutyryl cyclic AMP (dbcAMP). Our results indicate that testosterone is the main testicular androgen in this species. Furthermore, marked changes in the distribution of steroids were observed according to the zone of spermatogenesis, testosterone concentrations being highest in zones A and D. The relative contents of this hormone (steroid levels normalized to an equivalent number of Sertoli cells) as well as of delta 4-androstenedione and of progesterone increased from A to D. The concentrations of delta 4-androstenedione and progesterone were highest in zone D. Relative contents of 5 alpha-androstane-3 alpha,17 beta-diol, dihydrotestosterone and 11-ketotestosterone were very low in A when compared with the other zones. Finally, whereas no significant stage-related variation in the concentration of oestradiol-17 beta and 17 alpha-hydroxy, 20 beta-dihydroprogesterone was observed, the relative content of these steroids was lowest in zone A. Incubation experiments revealed that dogfish pituitary extract and dbcAMP can stimulate androgen synthesis (about twofold) and that a stage-related change of steroid responsiveness to dbcAMP exists (only zones A and D were responsive). Overall, the results of this study indicate that germ cells most probably influence Sertoli cell steroidogenesis and responsiveness in the adult dog fish testis.