Uptake of Norepinephrine as a Determinant of the Magnitude of the Inotropic Response ∗

Summary

The magnitude of the inotropic and chronotropic responses to norepinephrine and uptake of its tritiated isomer (NE-³H) were studied in isolated perfused rat hearts. A statistically significant inverse correlation between the uptake of (NE-³H) and the magnitude of the inotropic response was demonstrated. This correlation disappeared when the hearts were pretreated with cocaine or when uptake of and response to tritiated isoproterenol rather than NE-³H were examined. The variability of the inotropic responses to norepinephrine after cocaine or to isoproterenol were significantly less than responses to norepinephrine in the absence of any pretreatment. These results support the hypothesis which envisions the neuronal uptake of norepinephrine as an important mechanism in the determination of the magnitude of the adrenergic response to exogenous norepinephrine.