Effects of serotonin on the contractile state of the myocardium

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Abstract
Although serotonin [5-Hydroxytryptamine] produces widespread cardiovascular effects in the intact organism, direct effects on ventricular myocardium have not been well defined. Effects of a wide concentration range of 5-Hydroxytryptamine were studied in cat papillary muscles and canine right-heart-bypass preparations with bilateral carotid sinus and vagal nerve resection, 5-Hydroxytryptamine (30 [mu]g/ml) increased the average peak tension of papillary muscles from 5.4 to 8.8 g/mm2; in 4 intact left ventricles, left atrial infusion (42 [mu]g/kg per min.) increased average peak tension from 123.8 to 155.3 g/cm2 and increased stroke volume, peak aortic flow rate, and peak left ventricular dp/dt at constant left ventricular end-diastolic pressure, mean aortic pressure, and heart rate. In all cases rate of tension development was increased without changes in time to peak tension. Thus 5-Hydroxytryptamine can be shown to exert a direct positive inotropic effect on mammalian myocardium.