Evidence that inhibitory neurotransmission differs between the proximal and distal segments of guinea-pig taenia caeci

The effect of atropine (1 mu M) and N-G-nitro-L-arginine (L-NOARG, 10 mu M) on electrical field stimulation induced relaxation in proximal and distal segments of guinea-pig taenia caeci in the presence of guanethidine (4 mu M ) was studied. The frequency-dependent relaxations were lower in proximal t han in distal segments both in the presence and in the absence of atropine. The effect of L-NOARG tan inhibitor of nitric oxide (NO) synthase) on rela xation in the presence of atropine depended on the frequency of electrical stimulation and the segment used; the effect of L-NOARG was greater in prox imal segments than in distal segments. In the absence of atropine, the inhi bitory effect of L-NOARG was the same in both segments at all frequencies t ested. This study demonstrates differences between the opposite extremes of guinea-pig taenia caeci in relaxations induced by electrical stimulation. Our data also show a role of NO that is dependent on the integrity of choli nergic transmission. (C) 1999 Elsevier Science B.V. All rights reserved.