Effects of Epinephrine and 5-Hydroxytryptamine on Strips of Frog and Turtle Ventricle.

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Abstract
Ventricular strips were suspended in air, superfused with buffered Ringers, and driven electrically. Threshold, conduction time, QT interval (refractory period), and isometric force were measured. Ouabain and procainamide elicited familiar and characteristic effects. Contrary to published reports epinephrine increased contractile force (turtle and frog strips) but did not affect other parameters. Hydroxytryptamine (5-HT) was essentially inactive when applied in neutral, acid, or alkaline solutions. Epinephrine and 5-HT occasionally produced periods of autorhythmicity.