Central injection of TRH or its stable analog,
RX77368, produces a vagal
cholinergic stimulation of gastric acid secretion, mucosal blood flow and motor function. In the present study, we have investigated the contribution of
capsaicin-sensitive vagal afferent fibers to the gastric responses to intracisternal injection of
RX77368. Gastric acid secretion, measured in acute
gastric fistula rats anesthetized with
urethane, in response to intracisternal injection of
RX77368 (3-30 ng) was reduced by 21-65% by perineural pretreatment of the vagus nerves with
capsaicin 10-20 days before experiments. The increase in gastric mucosal blood flow measured by
hydrogen gas clearance induced by intracisternal injection of
RX77368 (30 ng) was also reduced by 65% in
capsaicin-pretreated rats. In contrast, increases in gastric motor function measured manometrically or release of gastric
luminal serotonin in response to intracisternal injection of
RX77368 (3-30 ng) were unaltered by
capsaicin pretreatment. The mechanism by which vagal afferent fibers contribute to the secretory and blood flow responses to the stable TRH analog is unclear at present, but it is possible that the decrease in gastric mucosal blood flow by lesion of
capsaicin-sensitive vagal afferents limits the secretory response.