A study of the actions of histamine on the isolated rat heart.
1. The effects of histamine on cardiac force, heart rate and coronary perfusion pressure were studied in the isolated rat heart, using the Langendorff perfused heart preparation. 2. Single injections of histamine induced dose-dependent decreases in contractile amplitude, heart rate and coronary perfusion pressure. 3. Perfusions of metiamide (above 1 x 10(-4) m) had a depressant effect on contractile force and heart rate, whereas diphenhydramine (4 x 10(-6) m) reduced only the heart rate. Both agents caused a fall in coronary perfusion pressure. 4. The negative inotropic and chronotropic effects of histamine on the isolated rat heart were not significantly influenced by either metiamide of diphenhydramine, or a combination of these drugs. However, the fall in coronary perfusion pressure induced by injections of histamine was significantly antagonized by metiamide or diphenhydramine. 5. These results suggest that the effects of histamine on the isolated rat heart may not be due entirely to stimulation of H1- or H2-receptors on the cardiac muscle cells. Evidence is presented for the existence of histamine H1- and H2-receptors in the coronary vessels.
D000818:Animals; D001794:Blood Pressure / Q000187:drug effects; D003326:Coronary Circulation / Q000187:drug effects; D004155:Diphenhydramine / Q000494:pharmacology; D006321:Heart / Q000187:drug effects*; D006339:Heart Rate / Q000187:drug effects; D006632:Histamine / Q000494:pharmacology*; D066298:In Vitro Techniques; D008297:Male; D008785:Metiamide / Q000494:pharmacology; D009200:Myocardial Contraction / Q000187:drug effects; D051381:Rats; D011969:Receptors, Histamine H1 / Q000187:drug effects; D011970:Receptors, Histamine H2 / Q000187:drug effects
D011969:Receptors, Histamine H1; D011970:Receptors, Histamine H2; D008785:Metiamide; D006632:Histamine; D004155:Diphenhydramine