Central vagal activation by TRH induces gastric hyperemia: role of CGRP in capsaicin-sensitive afferents in rats.

The role of calcitonin gene-related peptide (CGRP) in the vagal cholinergic-mediated increase in gastric mucosal blood flow (GMBF) induced by the stable thyrotropin-releasing hormone (TRH) analogue RX-77368 injected intracisternally (ic, 30 ng) was investigated in urethan-anesthetized rats using the hydrogen gas clearance technique. alpha-CGRP (14 micrograms.kg-1.h-1) or bethanechol (150 micrograms.kg-1.h-1) infused close intra-arterially to the stomach or RX-77368 injected intracisternally increased GMBF by 76, 102, and 131%, respectively, 30 min after administration. The CGRP antagonist, human CGRP-(8-37) [hCGRP-(8-37)], injected intravenously (15 micrograms/kg bolus and 3 micrograms.kg-1.h-1) inhibited by 100, 97, and 73% the gastric hyperemic response to alpha-CGRP, TRH analogue, and bethanechol, respectively, whereas the substance P antagonist CP-96,345 (3 mg/kg iv) had no effect. In capsaicin-pretreated rats, hCGRP-(8-37) no longer blocked the increase in GMBF induced by intracisternal RX-77368. These results suggest that the gastric hyperemic response to central vagal activation induced by intracisternal TRH analogue at 30 ng is mediated by local effector function of capsaicin-sensitive afferent fibers releasing CGRP.