Stimulating intestinal afferents reflexly activates cardiovascular system in cats

Abstract

Capsaicin and bradykinin stimulate afferents from certain viscera to reflexly activate the cardiovascular system; however, whether these agents evoke similar reflex responses when applied topically to the intestine is not known. Therefore, in cats anesthetized with methoxyflurane, we applied capsaicin (10 μg) or bradykinin (0.5 μg) to the serosol surface of the jejunum. Additionally, we topically applied bethanechol chloride,a synthetic choline ester with little direct cardiovascular effects, to evoke marked contraction of the smooth muscle of the jejunum. Capsaicin evoked significant (P < 0.05) increases in mean arterial pressure (105 ± 4 to 119 ± 4 mmHg, mean ± SE), first derivative left ventricular pressure (dP/dt) at 40 mmHg (2,698 ± 134 to 3,105 ± 155 mmHg/s), systemic vascular resistance (0.63 ± 0.15 to 0.68 ± 0.15 peripheral resistance units), and heart rate (196 ± 14 to 205 ± 15 beats/min), whereas aortic flow did not change. In a dose-dependent fashion, bradykinin and bethanechol each caused cardiovascular activation as well as a marked contraction of the smooth muscle in the segment of jejunum to which they were applied. In contrast, capsaicin produced no detectable contraction of visceral smooth muscle. Removal of the celiac and superior mesenteric ganglia abolished the cardiovascular responses evoked by capsaicin and bradykinin. Thus, in cats, stimulating intestinal afferents by topically applying capsaicin or bradykinin reflexly activates the cardiovascular system. Furthermore, although mechanoreceptors may contribute to the responses evoked by bradykinin and bethanechol, the capsaicin-related responses likely are mediated exclusively by chemically sensitive receptors.