EXCITATORY RESPONSE OF RABBIT MYOMETRIUM TO NITRIC-OXIDE IN-VITRO

Nitric oxide (NO) at high concentration (approx. 33 mu M) produced a m arked excitation: increase of tension development or increase in ampli tude of spontaneous contraction, in 7 out of 8 rabbit nonpregnant myom etrial strips. One case produced an inhibition: disappearance of spont aneous contraction. A latent period of several sec usually preceded th e excitation. The response of the myometrium to NO approx. 33 mu M ass ociated with remarkable increase in tissue cyclic GMP levels. NO appro x. 33 mu M reduced an inhibition, in 1 out of 3 myometrial strips take n from ovariorectmized rabbits. Two cases produced an excitatory. A pr ecusor of NO, L-Arginine 100 mu M or an inhibitor of NO synthase, N-G- nitro-L-arginine 100 mu M also produced a transient weak excitatory re sponse. On the contrary, 8-bromo-cyclic GMP 100 mu M produced an inhib ition. The excitatory response to NO 33 mu M was almost unaffected by pretreatment with indomethacin 10 mu M, whereas the spontaneous motili ty was remarkably depressed. The contractile response of the isolated rabbit myometrium to electrical field stimulation was almost unaffecte d by the pretreatment with L-arginine 100 mu M or N-G-nitro-L-arginine 100 mu M. The present findings may indicate that NO has inhibitory an d excitatory components on the mechanical activity of the rabbit isola ted myometrium.