Excitatory response of rabbit myometrium to nitric oxide in vitro

Nitric oxide (NO) at high concentration (approx. 33 microM) produced a marked excitation: increase of tension development or increase in amplitude of spontaneous contraction, in 7 out of 8 rabbit nonpregnant myometrial strips. One case produced an inhibition: disappearance of spontaneous contraction. A latent period of several sec usually preceded the excitation. The response of the myometrium to NO approx. 33 microM associated with remarkable increase in tissue cyclic GMP levels. NO approx. 33 microM reduced an inhibition, in 1 out of 3 myometrial strips taken from ovariectomized rabbits. Two cases produced an excitatory. A precursor of NO, L-Arginine 100 microM or an inhibitor of NO synthase, NG-nitro-L-arginine 100 microM also produced a transient weak excitatory response. On the contrary, 8-bromo-cyclic GMP 100 microM produced an inhibition. The excitatory response to NO 33 microM was almost unaffected by pretreatment with indomethacin 10 microM, whereas the spontaneous motility was remarkably depressed. The contractile response of the isolated rabbit myometrium to electrical field stimulation was almost unaffected by the pretreatment with L-arginine 100 microM or NG-nitro-L-arginine 100 microM. The present findings may indicate that NO has inhibitory and excitatory components on the mechanical activity of the rabbit isolated myometrium.