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      Comparison of the positive inotropic effects of serotonin, histamine, angiotensin II, endothelin and isoprenaline in the isolated human right atrium.

      Naunyn-Schmiedeberg's Archives of Pharmacology
      Adenylate Cyclase, drug effects, Adult, Aged, Angiotensin II, pharmacology, Biological Factors, Cardiotonic Agents, Dose-Response Relationship, Drug, Endothelins, Female, Heart Atria, Histamine, Humans, In Vitro Techniques, Inositol Phosphates, metabolism, Isoproterenol, Male, Middle Aged, Myocardial Contraction, physiology, Receptors, Cell Surface, Serotonin, Stimulation, Chemical

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          Abstract

          The receptor systems through which serotonin (5-HT), histamine, angiotensin II and endothelin increase the force of contraction were studied in isolated right atria from patients without apparent heart failure. All agonists increased the atrial force of contraction in a concentration-dependent manner; maximal effects, however, were significantly less than those evoked by isoprenaline or Ca2+. 5-HT and histamine, but not angiotensin II and endothelin, activated adenylate cyclase, whereas endothelin and angiotensin II stimulated inositol phosphate generation. Experiments with subtype-selective antagonists revealed that histamine effects were mediated by H2-receptors (sensitive to ranitidine), 5-HT-effects by 5-HT4-receptors (sensitive to SDZ 205-557) and angiotensin II effects by AT1-receptors (sensitive to losartan). We conclude that in human right atria the force of contraction can be increased by cyclic AMP-dependent (histamine, 5-HT) and -independent (angiotensin II, endothelin) pathways. Compared to beta-adrenoceptors, however, all other receptor systems increase the force of contraction only submaximally indicating that the beta-adrenoceptor pathway is the most important physiological mechanism to regulate force of contraction and/or heart rate in the human heart.

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