INVESTIGATION OF THE INFLUENCE OF PREGNANCY ON THE ROLE OF NITRIC-OXIDE IN GASTRIC-EMPTYING AND NONADRENERGIC NONCHOLINERGIC RELAXATION IN THE RAT

The influence of pregnancy on the role of nitric oxide (NO) in gastric emptying and in non-adrenergic noncholinergic (NANC) relaxation was s tudied in rats. The gastric emptying of a non-nutrient liquid solution and of poly-sterene beads was studied in non-pregnant (NP), 6 to 7 da ys pregnant (P7) and 18 to 20 days pregnant (P20) rats. Longitudinal m uscle strips of the gastric fundus and circular muscle strips of the p ylorus were isolated from NP and P20 rats and NANC relaxations were in duced by electrical field stimulation. The gastric emptying of the liq uid meal was significantly increased in P20 rats as compared to NP and P7 rats. In NP rats, NG-nitro-L-arginine methyl ester (L-NAME) dose-d ependently (50-150 mg/kg ip) reduced the gastric liquid emptying; the inhibitory effect of 100 mg/kg L-NAME ip was prevented by 400 mg/kg ip L-arginine and was mimicked by 100 mg/kg N-G-monomethyl-L-arginine (L -NMMA). The percentage inhibition of the liquid emptying by L-NAME did not differ between the 3 groups, except for the dose of 150 mg/kg ip where it was significantly lower in P20 rats. The gastric emptying of beads was 54% in NP, 36% in P7 and 69% in P20 rats but these values we re not significantly different illustrating the great variability. The inhibitory effect of L-NAME (25 and 100 mg/kg ip) on the emptying of beads did not differ between the 3 groups. As evaluated in NP rats, th e inhibitory effect of L-NAME on the gastric emptying of the beads was not prevented by L-arginine nor mimicked by L-NMMA. Electrical field stimulation in NANC conditions induced frequency-dependent relaxations in the fundus strips and relaxations followed by rebound contractions in the pyloric strips. These electrically induced NANC relaxations an d their reduction by 3x10(-4) M L-NAME were not different between NP a nd P20 rats. It can be concluded that no evidence for a regulatory rol e of NO in the gastric emptying of the beads was found, and that the n itrergic contribution to the gastric emptying of liquids and to the fu ndic and pyloric NANC relaxations was not influenced by pregnancy in r ats.