Increased reactivity to histamine in the coronary vascular system of the guinea-pig after endotoxin.

Histamine produced a dose-dependent increase in heart rate, myocardial contractility and coronary flow in the isolated guinea-pig heart using a modified Langendorff procedure. Intraperitoneal treatment of the guinea pigs with E. coli endotoxin, 4 days prior to the experiment, enhanced the positive chronotropic and flow-increasing effect of histamine. The increased response to histamine appeared to be H1-receptor mediated, the positive chronotropic response is attributed to H2-receptors. These results indicate that bacterial endotoxin increases the reactivity of the coronary vascular system of the guinea-pig to histamine.