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 cycla se activating polypeptide (PACAP) could regulate protein synthesis by enriched preparations of spermatocytes and spermatids from the adult r at testis. Spermatocytes and spermatids were incubated for 8 h or 24 h in the absence (control) or presence of PACAP-27, PACAP-38, vasoactiv e intestinal peptide (VIP) or dibutyryl adenosine-3',5'-cyclic monopho sphate (db-cAMP). Total synthesis of intracellular and secreted protei ns, during the incubation periods, was assessed and selected samples w ere analysed by 2-D SDS-PAGE. PACAP-38 (200 nM), VIP (200 nM) and db-c AMP (1 mM) significantly increased the synthesis of spermatocyte-secre ted and intracellular proteins by 8 h and 24 h. Synthesis of both intr acellular and secreted proteins by spermatids was significantly inhibi ted at 8 h and 24 h with PACAP, VIP and db-cAMP. The abundance of four germ cell-secreted proteins (GSP1, GSP2, GSP3 and phosphatidyethanola mine-binding protein (PEEP), which can be identified in both spermatoc yte and spermatid culture medium, and beta-actin, which can only be id entified in spermatid culture medium, was analysed. PACAP-38 and db-cA MP significantly increased the incorporation of label into GSP1, GSP2, GSP3 and PEEP, derived from spermatocyte culture medium, at 8 h and 2 4 h. In contrast PACAP-38 inhibited the incorporation of label into GS P1 and beta-actin, derived from spermatid culture medium, at 24 h. The results show that PACAP can regulate synthesis of both secreted and i ntracellular proteins by spermatids and spermatocytes in vitro. This e ffect is mimicked with high doses of db-cAMP (>1 mM), suggesting that PACAP may act via a pathway that involves changes in cyclic AMP concen tration in the germ cells.