Stimulation by bradykinin of HCO3- secretion in rat gastroduodenal mucosa

Background: We examined the effect of bradykinin on gastroduodenal HCO3- secretion in rats and investigated the mechanisms involved in this action. Material/Methods: Under urethane anesthesia, a chambered stomach or a proximal duodenal loop was perfused with saline, and the secretion of HCO3- was measured at pH 7.0 using a pH-stat method and by adding 2 mM HCl. Results: Intravenous administration of bradykinin increased both gastric and duodenal HCO3- secretion in a dose-dependent manner. These effects were totally blocked by FR172357, the bradykinin B2 receptor antagonist, and significantly attenuated by indomethacin or L-NAME, although the degree of inhibition was much greater in the stomach than the duodenum. Likewise, the response to bradykinin in the stomach totally disappeared on the chemical ablation of capsaicin-sensitive afferent neurons, whereas this action in the duodenum was inhibited only partially by sensory deafferentation. Capsazepine, the antagonist of transient receptor potential vanilloid type 1 (TRPV1), did not significantly affect the HCO3- response to bradykinin in these tissues. Conclusions: Bradykinin increases both gastric and duodenal HCO3- secretion through the activation of B2 receptors, and this action is mediated locally by endogenous prostaglandins (PGs) and nitric oxide (NO) as well as capsaicin-sensitive afferent neurons. It is assumed that bradykinin causes the release of PGs and NO as well as activation of afferent neurons via B2 receptors but not through the interaction with TRPV1, and these factors are all involved in the gastroduodenal responses, although the mode of interaction between these factors may be different in the stomach and duodenum.