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 inhib itor of guanylyl cyclase, and cAMP and cGMP analogs on oxytocin-induce d contractions have been studied in the testicular capsule of rats. Th e 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 w as produced by dibutyryl cAMP. Sodium nitroprusside facilitated oxytoc in-induced contractions. This effect was mimicked by dibutyryl cGMP. M ethylene blue, an inhibitor of soluble guanylyl cyclase, decreased oxy tocin-induced contractions, which suggests an involvement of guanylyl cyclase in the oxytocin effect. These results suggest that cAMP modula tes the contraction and that cGMP, contrary to that happens in most sm ooth muscles, could participate in oxytocin-induced contractions in th e testicular capsule of rats.