Pertussis toxin enhances follicle-stimulating hormone-stimulated cAMP production in rat seminiferous tubules in a stage-dependent manner.

Cyclic (c) AMP production was measured in vitro in dissected pieces of adult rat seminiferous tubules of defined stages of the seminiferous epithelial cycle (VII-VIII and XIV-IV) in the absence and presence of human follicle-stimulating hormone (FSH) (Metrodin, Serono). The basal rate of cAMP production was stage dependent, being about 2-fold higher in stages XIV-IV. FSH stimulated cAMP output in a time- and dose-dependent (stimulation at doses greater than or equal to 3 mg/l) fashion, and also the stimulability of stages XIV-IV (on average 2-fold) was greater than that of stages VII-VIII. When the tubular pieces were incubated in the presence of pertussis toxin (PT, 100 micrograms/l), the FSH-stimulated cAMP production of stages VII-VIII was enhanced by about 2-fold (P less than 0.01) whereas the basal rate was unaffected. In contrast, neither the basal nor the FSH-stimulated cAMP production of stages XIV-IV were affected by PT. Presence of the Gi-protein in both stages studied was demonstrated with PT-induced ADP ribosylation. However, no release of a putative activator of the Gi-protein could be demonstrated into spent media of the seminiferous tubules when incubated with freshly separated tubules. It is concluded that the poor FSH stimulability in cAMP production of certain spermatogenic stages of adult seminiferous tubules is at least partly due to endogenous inhibitors acting through the inhibitory Gi-protein. This inhibition could be demonstrated in a stage-dependent manner, and was present in stages with the lowest production and least stimulability of cAMP production by FSH.