Centrally mediated effects of bromocriptine on cardiac sympathovagal balance

Bromocriptine, a dopamine agonist, is known to lower cardiovascular mortali ty in L-dopa-treated patients with Parkinson's disease, probably by reducin g the cardiac sympathetic activity. We aimed at unmasking the central effec ts of bromocriptine on the heart by power spectrum analysis. Ten healthy su bjects (aged 31 +/-2 years) in supine and sitting positions were evaluated after the administration of bromocriptine (2.5 mg) alone and after pharmaco logical 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 (in index of cardiac symp athovagal balance). With subjects in the supine position, bromocriptine alo ne induced a significant increase in the LF component and the LF/HF ratio, together with a reduction in norepinephrine plasma levels and blood pressur e 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 s itting position. After domperidone pretreatment, bromocriptine induced a re duction in the LF component and in the LF/HF ratio. The sitting position ca used an increase in heart rate and in the LF/HF ratio. We demonstrated both peripheral and central effects of bromocriptine. In particular, pretreatme nt with a peripheral antagonist (domperidone) allowed us to unmask the cent ral effect of bromocriptine on cardiac sympathetic drive.