PITUITARY ADENYLATE-CYCLASE ACTIVATING POLYPEPTIDE CAN REGULATE TESTICULAR GERM-CELL PROTEIN-SYNTHESIS IN-VITRO

The aim of this study was to explore whether pituitary adenylate cyclase activating polypeptide (PACAP) could regulate protein synthesis by enriched preparations of spermatocytes and spermatids from the adult rat testis. Spermatocytes and spermatids were incubated for 8 h or 24 h in the absence (control) or presence of PACAP-27, PACAP-38, vasoactive intestinal peptide (VIP) or dibutyryl adenosine-3',5'-cyclic monophosphate (db-cAMP). Total synthesis of intracellular and secreted proteins, during the incubation periods, was assessed and selected samples were analysed by 2-D SDS-PAGE. PACAP-38 (200 nM), VIP (200 nM) and db-cAMP (1 mM) significantly increased the synthesis of spermatocyte-secreted and intracellular proteins by 8 h and 24 h. Synthesis of both intracellular and secreted proteins by spermatids was significantly inhibited at 8 h and 24 h with PACAP, VIP and db-cAMP. The abundance of four germ cell-secreted proteins (GSP1, GSP2, GSP3 and phosphatidyethanolamine-binding protein (PEEP), which can be identified in both spermatocyte and spermatid culture medium, and beta-actin, which can only be identified in spermatid culture medium, was analysed. PACAP-38 and db-cAMP significantly increased the incorporation of label into GSP1, GSP2, GSP3 and PEEP, derived from spermatocyte culture medium, at 8 h and 24 h. In contrast PACAP-38 inhibited the incorporation of label into GSP1 and beta-actin, derived from spermatid culture medium, at 24 h. The results show that PACAP can regulate synthesis of both secreted and intracellular proteins by spermatids and spermatocytes in vitro. This effect is mimicked with high doses of db-cAMP (>1 mM), suggesting that PACAP may act via a pathway that involves changes in cyclic AMP concentration in the germ cells.