Effects of atipamezole— a selectiveα2-adrenoceptor antagonist— on cardiac parasympathetic regulation in human subjects.

1 This double-blind, cross-over, placebo-controlled study on six healthy male volunteers was designed to evaluate the effects ofα₂-adrenoceptor antagonism on cardiac parasympathetic regulation.2 The subjects received atipamezole intravenously as a three-step infusion, which aimed at steady-state serum concentrations of 10, 30 and 90 ng ml⁻¹ at 50-min intervals.3 Drug effects were assessed with repeated recordings of blood pressure and electrocardiogram, in which the high-frequency (0.15–0.40 Hz) R-R interval variation is supposed to reflect cardiac parasympathetic efferent neuronal activity.4 At the end of the three steps of the infusion, the mean (±SD) concentrations of atipamezole were 10.5 (3.9), 26.8 (5.6) and 81.3 (21.1) ng ml⁻¹.5 Within this concentration range, atipamezole appeared to reduce slightly the high-frequency R-R interval fluctuations, indicating a minor vagolytic effect in the heart.6 Atipamezole increased systolic and diastolic arterial pressure, on average by 20 and 14 mmHg (maxima at the second step of the infusion), which evidently reflects an overall sympathetic augmentation. [ABSTRACT FROM AUTHOR]