EFFECTS OF HISTAMINE ON PORCINE ISOLATED MYOCARDIUM - DIFFERENTIATIONFROM EFFECTS ON HUMAN TISSUE

Inotropic effects of histamine have been studied extensively in many s pecies, but data on porcine myocardium, often used as a model for huma n heart, are not available. We investigated inotropic effects of hista mine on atrial and ventricular trabeculae obtained from porcine hearts . For comparison, we also evaluated the effects of histamine on human myocardium. Histamine caused concentration-dependent increases in cont ractile force in porcine and human atrial tissue [at 1 x 10(-3) M: 267 +/- 70 and 317 +/- 81 mg, or 133 +/- 17 and 85 +/- 12% of the respons e to 1 x 10(-5) M norepinephrine (NE), respectively], as well as in po rcine and human ventricular tissue (at 1 x 10(-3) M: 592 +/- 148 and 7 73 +/- 203 mg, or 68 +/- 13 and 122 +/- 61% of response to 1 x 10(-5) M NE, respectively). Cimetidine, but not mepyramine, antagonized the c ontractile effects of histamine in porcine and human atrial tissue and in human ventricular tissue. In contrast, the histamine-induced posit ive inotropic effect in porcine ventricular tissue was antagonized by mepyramine but not by cimetidine. Propranolol failed to block the inot ropic effect of histamine in all four tissues. These results indicate that, as with human atrial trabeculae, the positive inotropic effect o n porcine atrial trabeculae is mediated by H-2 receptors. In contrast to human ventricular trabeculae, however, the positive inotropic effec t on porcine ventricular trabeculae appears to be mediated by H-1 rece ptors.