Stimulatory Effect of Nitric Oxide on Bicarbonate Secretion in Bullfrog Duodenums in vitro

Abstract

The effect of nitric oxide (NO) on HCO^–₃ secretion was examined in vitro using an isolated preparation of bullfrog duodenum. The tissue was bathed in unbuffered Ringer’s solution gassed with 100% O₂ on the mucosal side and HCO^–₃ Ringer’s solution gassed with 95% O₂–5% CO₂ on the serosal side. The HCO^–₃ secretion was measured by the pH-stat method using 2 mmol/l HCl as the titrant to keep the mucosal pH at 7.4. (±)-(E)-Ethyl-2-[(E)-hydroxyimino]-5-nitro-3-hexenamine (NOR3) was used as a NO donor and added to the serosal solution. To analyze the NOR3 action on HCO^–₃ secretion, the effects of dibutyryl adenosine-3′,5′-cyclic monophosphate (dbcAMP), dibutyryl guanosine-3′,5′-cyclic monophosphate (dbcGMP), methylene blue, and indomethacin on the HCO^–₃ response were also examined. NOR3 (1×10^–4 and 3×10^–4 mol/l) caused an increase in HCO^–₃ secretion in a dose-dependent manner, and this effect appeared with an about 30-min time lag, reaching the level of 1.5–2.5 times greater than basal values at 1–2 h later. Both dbcAMP (1×10^–3 mol/l) and dbcGMP (1×10^–3 mol/l) also caused a significant increase in HCO^–₃ secretion in bullfrog duodenums in vitro, although the onset of the HCO^–₃ response to dbcGMP was delayed as compared to the former. The stimulatory action of NOR3 on duodenal HCO^–₃ secretion was significantly attenuated by methylene blue (5×10^–5 mol/l) and indomethacin (1×10^–5 mol/l), the latter also inhibiting the HCO^–₃ response to dbcGMP. The release of prostaglandin E₂ in the serosal solution was significantly increased after addition of NOR3 (3×10^–4 mol/l) and dbcGMP (1×10^–3 mol/l) in an indomethacin-sensitive manner. These results suggest that the NO donor increases duodenal HCO^–₃ secretion in vitro, and this action of NO donor is cGMP-dependent and mediated by endogenous prostaglandins. Duodenal HCO^–₃ secretion may be regulated locally by NO/cGMP in addition to prostaglandin/cAMP.

Stimulation by nizatidine, a histamine H2-receptor antagonist, of duodenal HCO3-secretion in rats: relation to anti-cholinesterase activity

“…We previously reported that the HCO 3 -response induced by cholinergic agents was not affected by indomethacin [18] . Furukawa et al [25] reported that NO stimulates the HCO 3 -secretion, mediated by endogenous PGs in isolated bullfrog duodenums. Thus, it is reasonable that the HCO 3 -response induced by nizatidine is not affected by the NO synthase inhibitor L-NAME.…”

Distinct mechanisms of acid-induced HCO3−secretion in normal and slightly permeable stomachs

“…Uno et al (35) reported that the NO donor S-nitroso-N-acetyl penicillamine stimulates PGE 2 production in rat gastric epithelial cells. Furukawa et al (8) reported that both NOR-3 and dibubutyryl guanosine-3Ј,5Ј-cyclic monophosphate increased PGE 2 production in isolated bullfrog duodenums, suggesting a NO/cGMP-dependent increase in PG production. In the present study, the increased PGE 2 generation after the mucosal acidification was blocked not only by indomethacin but also by L-NAME.…”

“…Thus, it is also possible that mucosal acidification increases NO release through the stimulation of capsaicin-sensitive sensory neurons. On the other hand, several studies have reported that NO or NO donors stimulate PG production in various organs and cells (8,35,36). Uno et al (35) reported that the NO donor S-nitroso-N-acetyl penicillamine stimulates PGE 2 production in rat gastric epithelial cells.…”

Phosphodiesterase Isozymes Involved in Regulation of Secretion in Isolated Mouse Stomach in Vitro

“…The stimulatory effect of PGE 2 on HCO 3 Ϫ secretion in the stomach is known to be mediated by the activation of EP1 receptors and coupled intracellularly with Ca 2ϩ (Takeuchi et al, 1997b. In contrast, NO stimulates the secretion of HCO 3 Ϫ in the duodenum via the activation of soluble guanylate cyclase and an increase in the intracellular level of cGMP (Moncada et al, 1991;Furukawa et al, 1999;Sugamoto et al, 2001). We further showed that NOR-3, an NO donor, increased the secretion of HCO 3 Ϫ in the rat stomach, via endogenous PGE 2 in a cGMP-dependent manner .…”

“…It remains, however, unexplored which PDE isozyme(s) is involved in the regulation of gastric HCO 3 Ϫ secretion. The regulatory mechanism of HCO 3 Ϫ secretion differs in many points between the stomach and the duodenum; in the latter, the secretion is mediated intracellularly with both cAMP, cGMP, and Ca 2ϩ , whereas that in the stomach is intracellularly mediated by Ca 2ϩ and cGMP but not cAMP (Flemström, 1977(Flemström, , 1987Guba et al, 1996;Seidler et al, 1997;Takeuchi et al, 1997a;Furukawa et al, 1999;Rao et al, 2004;Sellers et al, 2005). Thus, there is a possibility that the PDE isozymes involved in the HCO 3 Ϫ response are different in these tissues.…”