Endocrine Abstracts

Previously, we have described an inhibitory role of melatonin (Mel) in the expression of StAR and key steroidogenic enzymes, as well as in the regulation of testosterone production in testes of Syrian hamsters. The goal of the present work was to further investigate the signaling pathway involves in the testicular action of Mel. Thus, Leydig cells were purified from reproductively active hamsters killed by asphyxia with carbon dioxide, and incubated in the presence of Mel and MAPK blockers. Subsequently, the expression of c-jun, c-fos, phospho-c-jun, phospho-P42/44, phospho-P38 and phospho-JNK46/54 was evaluated by quantitative PCR and/or immunobloting, and the levels of testosterone released to the incubation media were determined by RIA.

Ten micromolar Mel significantly inhibited c-jun and c-fos expression after 30 min and 3 h incubation. Furthermore, we found a marked reduction in the phosphorylation of c-jun, P42/44, P38, and JNK46/54 in the presence of Mel. In addition, the incubation of hamster Leydig cells in the presence of blockers for P42/44 (U0126, 10 μM), JNK46/54 (SP600125, 20 μM) and P38 (SB203580, 10 μM) decreased the expression of c-jun and c-fos, and the production of testosterone.

In conclusion, our studies described an inhibitory role of Mel in the phosphorylation of c-jun, P42/44, P38, JNK46 and JNK54, and the expression of c-jun and c-fos. These factors might act as mediators in the Mel-dependent regulation of testosterone production in hamster Leydig cells.