INCREASED HISTAMINE AND 5-HT IN PORTAL-VEIN PLASMA AND MESENTERIC LYMPH DURING BRIEF ISCHEMIA AND REPERFUSION

Brief mesenteric ischemia (10 min) can stimulate both visceral A delta - and C-fiber afferents and evoke reflex excitation of the cardiovascu lar system. We have shown that exogenous histamine causes reflex cardi ovascular responses and that intra-arterial injection of 5-hydroxytryp tamine (5-HT) into a mesenteric artery stimulates visceral A delta- an d C-fiber afferents. We therefore hypothesized that brief abdominal is chemia is associated with release of histamine and 5-HT into the inter stitium, where these mediators could stimulate or sensitize ischemical ly sensitive visceral afferent nerve endings. Accordingly, we measured concentrations of histamine and 5-HT in portal venous blood plasma an d intestinal lymph fluid in cats. Cannulas were placed in a portal vei n and in an intestinal lymphatic duct distal to the lymph node. Lymph and plasma histamine and 5-HT concentrations were measured by high-per formance liquid chromatography before, during, and immediately after 1 0-min occlusion of the descending thoracic aorta. Histamine concentrat ion increased significantly (P < 0.01) in portal venous blood plasma f rom a preocclusion level of 2.2 +/- 0.6 to 4.6 +/- 1.0 and 6.4 +/- 1.3 nmol/ml and in lymph fluid from a preocclusion level of 3.4 +/- 1.0 t o 6.3 +/- 1.3 and 6.4 +/- 1.3 nmol/ml (n = 18) during brief ischemia a nd reperfusion, respectively. Also, the 5-HT concentration was signifi cantly (P < 0.01) elevated in portal venous blood plasma from a preocc lusion concentration of 1.1 +/- 0.5 to 2.7 +/- 0.8 and 2.5 +/- 0.8 nmo l/ml and in lymph from a preocclusion level of 1.8 +/- 0.7 to 4.0 +/- 1.4 and 4.6 +/- 1.3 nmol/ml (n = 13) during brief ischemia and reperfu sion, respectively. Because visceral afferent nerve endings are locate d in the interstitium, elevation of the interstitial concentration of histamine and 5-HT may contribute to the stimulation or sensitization of these nerve terminals during the brief ischemia and reperfusion per iod.