Centrally mediated effects of bromocriptine on cardiac sympathovagal balance.

Bromocriptine, a dopamine agonist, is known to lower cardiovascular mortality in L-dopa-treated patients with Parkinson's disease, probably by reducing the cardiac sympathetic activity. We aimed at unmasking the central effects of bromocriptine on the heart by power spectrum analysis. Ten healthy subjects (aged 31+/-2 years) in supine and sitting positions were evaluated after the administration of bromocriptine (2.5 mg) alone and after pharmacological peripheral D(2)-like blockade by domperidone (20 mg). We calculated (autoregressive method) the following: the low-frequency (LF) component (an index of cardiac sympathetic tone), the high-frequency (HF) component (an index of cardiac vagal tone), and the LF/HF ratio (an index of cardiac sympathovagal balance). With subjects in the supine position, bromocriptine alone induced a significant increase in the LF component and the LF/HF ratio, together with a reduction in norepinephrine plasma levels and blood pressure values. These conflicting effects can be explained as the combined result of direct and indirect (reflex-mediated) actions of bromocriptine in vivo. No changes in cardiac autonomic drive were observed with subjects in the sitting position. After domperidone pretreatment, bromocriptine induced a reduction in the LF component and in the LF/HF ratio. The sitting position caused an increase in heart rate and in the LF/HF ratio. We demonstrated both peripheral and central effects of bromocriptine. In particular, pretreatment with a peripheral antagonist (domperidone) allowed us to unmask the central effect of bromocriptine on cardiac sympathetic drive.