Role of 5α-dihydrotestosterone in testicular development of gilthead seabream following finasteride administration

In teleosts, spermatogenesis is regulated by pituitary gonadotropins and sex steroids. 5 alpha-dihydrotestosterone (DHT), derived from testosterone (T) through the action of 5 alpha-reductase, has recently been suggested to play a physiologically important role in some fish species. In this study, gilthead seabream, Sparus aurata L., males received an implant of 1 mu g T/g body mass (bm) or vehicle alone and, 7 days later, 1 mg finasteride (FIN, an inhibitor of 5 alpha-reductase)/kg bm or vehicle. Serum levels of T, 11-ketotestosterone (11KT), DHT and 17 beta-estradiol (E-2), and the mRNA levels of the main enzymes involved in their synthesis, were analysed. T promoted a transient increase in the serum levels of T, 11KT and E-2 but a decrease in those of DHT at day 15 following T injection, in accordance with the up-regulation of mRNA levels of the enzymes involved in T transformation to 11KT (coding genes: cyp11b1 and hsd11b) and the down-regulation of mRNA levels of the enzyme responsible for T transformation to DHT (coding gene: srd5a). Interestingly, a similar effect was observed when FIN was injected. However, when fish were injected with T and FIN successively (T + FIN), control levels were not recovered at the end of the experimental period (28 days). DHT seems to regulate E-2 serum levels via the down regulation of mRNA levels of aromatase (coding gene: cypl9ala), which is needed for the transformation of T into E-2. The testis histology, together with the proliferative rates recorded upon T, FIN or T + FIN treatment, suggests that DHT is involved in the onset of the meiotic phase of spermatogenesis.