1. Archive
2. Vol.51, No.3

Laterality in Direct and Indirect Inotropic Effects of Sympathetic Stimulation in Isolated Canine Heart

Abstract: Although sympathetic nerve stimulation is known to increase ventricular contractility, concomitant increases in heart rate (HR) make it difficult to separate its direct inotropic effect from indirect inotropic effect through a force-frequency mechanism. We stimulated the stellate ganglia in 8 isolated canine hearts with functional sympathetic nerves. Right sympathetic stimulation at 10 Hz increased ventricular end-systolic elastance (E_es) by 95.7 ± 7.5% (p < 0.001) and HR by 32.5 ± 4.2% (p < 0.05). In contrast, left sympathetic stimulation at 10 Hz increased E_es by 70.7 ± 6.5% (p < 0.001) without significant changes in HR. Preventing the chronotropic response by fixed-rate pacing attenuated the E_es response to right sympathetic stimulation at 5 Hz (52.0 ± 5.1 vs. 22.8 ± 2.8%, p < 0.001), but not to left sympathetic stimulation at 5 Hz (54.5 ± 3.4 vs. 53.3 ± 2.2%, NS). In the isolated canine heart, the right sympathetic nerve affected E_es by both the direct inotropic effect and the indirect HR-dependent inotropic effect. In contrast, the left sympathetic nerve regulated E_es primarily by its direct inotropic effect.

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