Role of cyclic nucleotides in contraction induced by oxytocin in the testicular capsule of the rat in vitro.

The effects of phosphodiesterase inhibitors, an activator and an inhibitor of guanylyl cyclase, and cAMP and cGMP analogs on oxytocin-induced contractions have been studied in the testicular capsule of rats. The nonspecific phosphodiesterase inhibitors, theophylline and caffeine, attenuated the oxytocin-induced contractions via mechanisms that seem to be related to an increase in cAMP levels, since a similar effect was produced by dibutyryl cAMP. Sodium nitroprusside facilitated oxytocin-induced contractions. This effect was mimicked by dibutyryl cGMP. Methylene blue, an inhibitor of soluble guanylyl cyclase, decreased oxytocin-induced contractions, which suggests an involvement of guanylyl cyclase in the oxytocin effect. These results suggest that cAMP modulates the contraction and that cGMP, contrary to what happens in most smooth muscles, could participate in oxytocin-induced contractions in the testicular capsule of rats.