Investigation of the influence of pregnancy on the role of nitric oxide in gastric emptying and non-adrenergic non-cholinergic relaxation in the rat

Abstract

The influence of pregnancy on the role of nitric oxide (NO) in gastric emptying and in non-adrenergic non-cholinergic (NANC) relaxation was studied in rats. The gastric emptying of a non-nutrient liquid solution and of polysterene beads was studied in non-pregnant (NP), 6 to 7 days pregnant (P7) and 18 to 20 days pregnant (P20) rats. Longitudinal muscle strips of the gastric fundus and circular muscle strips of the pylorus were isolated from NP and P20 rats and NANC relaxations were induced by electrical field stimulation. The gastric emptying of the liquid 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-dependently (50-150 mg/kg i.p.) reduced the gastric liquid emptying; the inhibitory effect of 100 mg/kg L-NAME i.p. was prevented by 400 mg/kg i.p. L-arginine and was mimicked by 100 mg/kg NG-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 i.p. 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 were not significantly different illustrating the great variability. The inhibitory effect of L-NAME (25 and 100 mg/kg i.p.) on the emptying of beads did not differ between the 3 groups. As evaluated in NP rats, the 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 and their reduction by 3x 10(-4) M L-NAME were not different between NP and P20 rats. It can be concluded that no evidence for a regulatory role of NO in the gastric emptying of the beads was found, and that the nitrergic contribution to the gastric emptying of liquids and to the fundic and pyloric NANC relaxations was not influenced by pregnancy in rats.

Influence of Relaxin on the Neurally Induced Relaxant Responses of the Mouse Gastric Fundus1

“…Even if the influence of sex hormones and pregnancy on gastric motility and emptying is not definitively established [1,2,[36][37][38][39], the relaxin-induced increase in amplitude of the nitrergic fast relaxations may have some physiological implications. In fact, recent studies have shown that enhanced nitrergic relaxations can be observed in the stomach of pregnant animals and that estrogens could enhance gastric transit time by increasing the amplitude of the relaxant responses [19].…”

“…The exact role of the nitrergic NANC innervation and of the relaxant responses in gastric transit time is far from being clarified [19,38,40,41]. Nevertheless, it is widely accepted that an altered NO production may lead to gastrointestinal dysmotilities [42].…”

Relaxin counteracts the altered gastric motility of dystrophic (mdx) mice: functional and immunohistochemical evidence for the involvement of nitric oxide

“…Evidence exists that sex hormones influence gastrointestinal motility (21,32,37,38,40) and may contribute to the increase of NOS expression and NO production occurring in pregnancy (55,61). The identification of specific relaxin-binding sites in the smooth muscle cells of the gastrointestinal tract of pregnant pigs (42) suggests that this hormone also influences gut func- tions, in keeping with early reports that a relaxin preparation extracted from the ovary reduced the strength and the frequency of contractions in the rat ileum (26) and that relaxin had disruptive effects on the migrating myoelectric complex in the rat small intestine (25).…”