Vaginal Fluid Adenosine 3',5'-Cyclic Monophosphate (cAMP) in the Rat: Interaction with Sperm cAMP-Dependent Protein Kinase Regulatory Subunits

Abstract

Cyclic AMP (adenosine 3',5'-cyclic monophosphate) concentrations were determined in rat vaginal fluids throughout the estrous cycle. Radioimmunoassay results demonstrated that estrus and early metestrus vaginal fluids had significantly (p < 0.01) elevated cAMP concentrations compared to pro-estrus, late metestrus, and early and late diestrus. Ovariectomy reduced RIA-detectable cAMP in vaginal fluid. When cauda sperm were preincubated for 5 min with vaginal fluids from each stage of the estrous cycle, results demonstrated that only estrus- and early metestrus-stage vaginal fluids caused a decrease in [³²P]-8N₃cAMP (8-azido photoaffinity analogue of cAMP) photolabeling of sperm cAMP-dependent protein kinase regulatory subunits RI and RII. To examine if this reduction in [³²P]-8N₃cAMP photoincorporation by sperm RI and RII could be due to endogenous cAMP, vaginal fluids were boiled, trypsinized, and/or incubated with EGTA or phosphodiesterase. Only phosphodiesterase-treated vaginal fluids restored sperm regulatory subunit photoincorporation of [³²P]-8N₃cAMP. It is suggested that cAMP is present in rat vaginal fluids during the estrous cycle in a concentration sufficient to bind the regulatory subunits of rat sperm cAMP-dependent protein kinase.

Key Words:

• Rat epididymal sperm
• Vaginal fluids
• 8-Azido photoprobes
• [³²P]-8N₃cAMP.