cyclic-gmp and vasoactive-intestinal-peptide-(10-28)

Participation of the nitric oxide-cyclic GMP pathway in nonadrenergic, noncholinergic (NANC) relaxation induced by electrical field stimulation of longitudinal muscle of the rectum of Wistar-ST rats was studied by using a selective inhibitor of soluble guanylyl cyclase, 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (ODQ). ODQ concentration dependently inhibited the relaxation and at 10 microM, maximally inhibited it by 83%. However, results obtained with N(G)-nitro-L-arginine, L-arginine and exogenously added nitric oxide excluded the participation of nitric oxide in the relaxation. An inhibitor of cyclic GMP-dependent protein kinase (PKG) partially (39%) inhibited the relaxation. ODQ also significantly inhibited the relaxation, which persisted after the PKG inhibitor-treatment, by 85%. The results strongly suggest that ODQ inhibits the NANC relaxation in a cyclic GMP-PKG pathway-independent manner.

Topics: Animals; Cyclic GMP; Cyclic GMP-Dependent Protein Kinases; Enzyme Inhibitors; Guanylate Cyclase; In Vitro Techniques; Male; Muscle Relaxation; Neuropeptides; Nitroarginine; Oxadiazoles; Peptide Fragments; Pituitary Adenylate Cyclase-Activating Polypeptide; Quinoxalines; Rats; Rats, Wistar; Rectum; Vasoactive Intestinal Peptide

The mediators of nonadrenergic, noncholinergic (NANC) relaxation of the circular muscle of rat rectum were examined in vitro. In the circular muscle of rat rectum, NG-nitro-L-arginine (L-NOARG) at 10 microM did not affect electrical field stimulation-induced relaxation but at 100 microM it inhibited electrical field stimulation-induced relaxation by about 75% and 1-mM L-arginine reversed the inhibition. Exogenous nitric oxide (NO) (1-10 microM) concentration dependently relaxed the circular muscle. Electrical field stimulation increased the cyclic GMP content of the circular muscle to about twice its resting level. L-NOARG, even at 10 microM, completely inhibited the electrical field stimulation-induced elevation of cyclic GMP content. However, L-arginine at 1 mM did not reverse the inhibition in cyclic GMP content. Inhibitory junction potentials (i.j.ps) induced by electrical field stimulation in the circular muscle cells were not affected by L-NOARG, 100 microM. Apamin ( < or = microM) did not affect the electrical field stimulation-induced relaxation, but almost completely inhibited electrical field stimulation-induced i.j.ps. NO (0.3-10 microM) induced relaxation of the circular muscle with a concomitant decrease in intracellular Ca2+ level ([Ca2+]i). Abundant immunoreactivity of NO synthase was found in the circular muscle layer, in addition to myenteric and submucosal plexus. The results suggest that NO induces NANC relaxation with a concomitant change in [Ca2+]i in the circular muscle of rat rectum. However, the involvement of changes in cyclic GMP level and in membrane potentials in the mechanism was not shown in the present experimental conditions.

Topics: Animals; Arginine; Calcium; Cyclic GMP; Electric Stimulation; Immunohistochemistry; In Vitro Techniques; Male; Membrane Potentials; Muscle Contraction; Muscle Relaxation; Muscle, Smooth; Myenteric Plexus; Neuropeptides; Nitric Oxide; Nitric Oxide Synthase; Nitroarginine; Peptide Fragments; Pituitary Adenylate Cyclase-Activating Polypeptide; Potassium Channel Blockers; Rats; Rats, Wistar; Rectum; Vasoactive Intestinal Peptide