Steroid production in toads

CANOSA LF; POZZI AG; ROSEMBLIT C; CEBALLOS NR

JOURNAL OF STEROID BIOCHEMISTRY AND MOLECULAR BIOLOGY

Año: 2003 vol. 85 p. 227 - 233

0960-0760

In Bufo arenarum, androgen biosynthesis occurs through a complete 5-ene pathway, including 5-androstane-3
,17
-diol as the immediateprecursor of testosterone. Besides, steroidogenesis changes during the breeding period, turning from androgens to C21-steroidssuch as 5-pregnan-3,20-diol, 3-hydroxy-5-pregnan-20-one and 5-pregnan-3,20-dione. In B. arenarum, steroid hormones arenot involved in hCG-induced spermiation, suggesting that the steroidogenic shift to C21-steroids during the breeding be not related tospermiation. The activity of 17-hydroxylase-C17–20 lyase (CypP450c17) decreases during the reproductive season, suggesting that thisenzyme would represent a key enzyme in the regulation of seasonal changes. However, the increase in the affinity for pregnenolone of3
-hydroxysteroid dehydrogenase (3HSD)/isomerase could also be involved. Moreover, the reduction in CypP450c17 leading to a reductionin C19-steroids, among them dehydroepiandrosterone (DHE), would contribute to the conversion of pregnenolone into progesterone,avoiding the non-competitive inhibition exerted by DHE on this transformation. Additionally, CypP450c17 possesses a higher affinity forpregnenolone than for progesterone, explaining the predominance of the 5-ene pathway for testosterone biosynthesis. Animals in reproductivecondition showed a significant reduction in circulating androgens, enhancing the physiological relevance of all the in vitro results.The in vitro effects of mGnRH and hrFSH on testicular steroidogenesis revealed that both hormones inhibited CypP450c17 activity. Insummary, these results demonstrate that, in B. arenarum, the change in testicular steroidogenesis during the reproductive period could bepartially due to an FSH and GnRH-induced decrease in CypP450c17 activity.