Effect of metoclopramide on muscle sympathetic nerve activity in humans.

For determining the effect of the activation of the central cholinergic system on the sympathetic nervous system, we measured muscle sympathetic nerve activity (MSNA) together with heart rate and blood pressure before and after an intravenous injection of metoclopramide. Immediately after metoclopramide injection, short-term increases in MSNA and heart rate followed a transient decrease in blood pressure, suggesting that increased sympathetic nerve activity may result from the unloading of arterial baroreceptors. Approximately 7 min after injection, MSNA and heart rate were again notably increased, followed by an increase in blood pressure. This late increase in MSNA may result from central activation of the sympathetic nervous system, but not as a result of the unloading of arterial baroreceptors. The results of this study suggest that metoclopramide activates the sympathetic nervous system by mediating the central cholinergic system in humans.