NO mediates gastric relaxation after brief vagal stimulation in anesthetized dogs

In vitro studies showed that relaxations induced after vagal stimulation of the guinea pig stomach are mediated via nitric oxide (NO). The role of NO in canine gastric relaxation in response to vagal stimulation has as yet not been studied. The present study examined the influence of NG-nitro-L-arginine (L-NNA) on gastric relaxations after vagal nerve stimulation in the anesthetized dog. In beagle dogs (n = 7), the ventral and dorsal abdominal vagal nerves were connected to a pair of platinum electrodes. Gastric tone was measured by means of a barostat. Changes in gastric motility were measured with force transducers sutured on the fundus and the antrum. The cervical vagi were sectioned, and dogs were given atropine (0.2 mg/kg i.v.) and guanethidine (5 mg/kg i.v.). Electrical stimulation of the vagal trunks (19 V, 1-ms duration, for 15 s every 2 min, 1-30 Hz) induced frequency-dependent increases in volume. On the fundus, frequency-dependent relaxations could be observed (maximal effect at 5 mmHg and at 10 Hz). During electrical stimulation, the spontaneous antral contractions were completely blocked. After cessation of the stimulus, "rebound" contractions could be observed. L-NNA (5 mg/kg i.v.) completely blocked the increases in gastric volume and the relaxations on the fundus. On the antrum, however, contractions were observed during the electrical stimulation. L-Arginine (250 mg/kg i.v.) gradually restored the relaxations on electrical stimulation. This study demonstrates that NO mediates short-lasting vagally induced gastric relaxations in the anesthetized dog.