Nitric oxide has tonic inhibitory effect, but is not involved in the vagal control or VIP effects on motility of the porcine antrum.

BACKGROUND

The involvement of nitric oxide (NO) in vagal control and vasoactive intestinal polypeptide (VIP)-induced effects on antral motility was studied using isolated perfused preparations of porcine gastric antrum with intact vagal innervation.

METHODS

The presence of NO and VIP-producing neurons was studied using immunohistochemistry and histochemical techniques. Widespread, but not total, co-localization of NO and VIP immunoreactivity was found in the submucosa and in the muscle layers.

RESULTS

Electrical stimulation of the vagus nerves for 5 min (8 Hz, 10 mA, 4 msec) increased the motility index from 2.47 = 0.44 to 11.50 +/- 2.02 (n = 5). This effect was not influenced by the two NO synthase inhibitors N-nitro-L-arginine methyl ester (10(-4) M) and NG-nitro-L-arginine (10(-5) M). However, infusion of inhibitors increased the spontaneous motility index from 2.40 +/- 0.08 to 5.36 +/- 1.08 (P < 0.05) and 3.05 +/- 1.10 to 4.14 +/- 1.04 (P < 0.05), respectively. The addition of L-arginine reversed this effect. Infusion of VIP 2 x 10(-9)M decreased the motility index from 2.32 +/- 0.43 to 1.32 +/- 0.27 (P < 0.05), an effect that was preserved during NO synthase inhibition. Electrical vagus stimulation increased the release of VIP to the venous effluent, an effect that persisted during NO synthase inhibitors.

CONCLUSION

We conclude that NO-producing nerves seem to have a tonic inhibitory action on the porcine antral motility, but are not involved in the motor effects of vagal stimulation or VIP infusion.