The effects of an intravenous nicardipine injection on baroreflex control of heart rate in man.

The effects of nicardipine injection on baroreflex control of heart rate were investigated by both pressor and depressor tests in 17 adult patients. Baroreflex sensitivity was attenuated after nicardipine injection by the pressor test using phenylephrine, whereas it was not changed by the depressor test using nitroglycerine. No resetting of the baroreflex occurred after nicardipine injection. By the pressor test, the plasma norepinephrine level was decreased, indicating that parasympathetic activity increased, and by the depressor test, the plasma norepinephrine concentration was increased, indicating that sympathetic activity increased. These results suggest that it is safe to use nicardipine clinically even when reduction in blood pressure for hypovolemia or unclamping the main artery is expected, and it is disadvantageous to administer the drug when an increase in blood pressure due to cross-clamping of the main artery is forecasted.