Forskolin stimulates bovine epididymal sperm motility and cyclic AMP levels

Forskolin, a diterpene, has been reported to reversibly stimulate adenylate cyclase from a number of mammalian tissues. Adenylate cyclase preparations derived from sperm are reported to be both deficient in the guanine nucleotide subunit and insensitive to forskolin. Despite the latter observation, we report here that forskolin elevates cAMP levels in immature caput sperm, and initiates motility in the presence of "permissive" agents such as bicarbonate, procaine and dibucaine. In mature caudal sperm forskolin stimulates motility in a concentration dependent manner in the presence of the phosphodiesterase inhibitor IBMX but elevates cAMP levels only briefly before nucleotide levels return to control values. In addition, forskolin stimulates adenylate cyclase activity associated with plasma membrane preparations of caput sperm but not caudal sperm. This differential action of forskolin on these cell types could provide a basis for understanding the regulation of adenylate cyclase in both immature and mature bovine sperm.