Pituitary adenylate cyclase-activating polypeptide regulates rat Leydig cell function in vitro

Area of Science:

• Reproductive Endocrinology
• Molecular Endocrinology
• Cell Signaling

Background:

• Pituitary adenylate cyclase-activating polypeptide (PACAP) is a peptide hormone with diverse physiological roles.
• Leydig cells are crucial for testosterone production in the testes.
• The role of PACAP and its interaction with other signaling molecules in testicular steroidogenesis requires further elucidation.

Purpose of the Study:

• To investigate the effects of PACAP-27 and PACAP-38 on testosterone, cAMP, and prostaglandin E2 (PGE2) production in rat Leydig cells.
• To examine the influence of vasoactive intestinal peptide (VIP) and specific receptor antagonists on testicular steroidogenesis.
• To determine the signaling pathways involved in PACAP-mediated steroidogenesis.

Main Methods:

• Purified rat Leydig cells were used for in vitro studies.
• Hormone production (testosterone, cAMP, PGE2) was measured under various treatment conditions.
• Specific antagonists for PACAP and VIP receptors were employed.
• The role of prostaglandin synthesis was assessed using indomethacin.

Main Results:

• PACAP-38, but not PACAP-27, potentiated testosterone production in response to human chorionic gonadotropin (hCG).
• VIP also increased basal and hCG-induced testosterone production.
• PACAP-38 dose-dependently increased cAMP and PGE2 production, though PGE2 was not essential for PACAP's steroidogenic effect.
• PACAP's effects were blocked by a PACAP antagonist, indicating receptor-mediated action.
• VIP's effects were blocked by a VIP antagonist.

Conclusions:

• PACAP-38 activates both cAMP- and phosphatidylinositol-dependent pathways in Leydig cells.
• PACAP-38 amplifies hCG-stimulated testicular steroidogenesis via specific PACAP receptors.
• These findings suggest the presence of type 1 PACAP receptors on rat Leydig cells.