VAGAL CARDIAC ACTIVITY IN ESSENTIAL-HYPERTENSION - THE EFFECTS OF METOPROLOL AND RAMIPRIL

Cardiovascular parasympathetic activity is attenuated in essential hyp ertension. Both beta-adrenoceptor antagonists and angiotensin converti ng enzyme inhibitors have been reported to increase vagal modulation o f heart rate and baroreflex sensitivity, but the relations between the antihypertensive and vagal cardiac effects of these drugs have remain ed unclear in essential hypertension. In the present study we evaluate d the effects of a 4-week crossover monotherapy with metoprolol and ra mipril on spectrum analysis indices of heart rate variability in the s upine rest and head-up tilted positions, baroreflex sensitivity (pheny lephrine method), and 24-h ambulatory blood pressure (BP) in 12 former ly untreated stage 1-2 essential hypertensive patients. Compared to th e pretreatment values, both drugs decreased BP similarly and significa ntly. However, the drugs showed different effects on cardiac vagal act ivity: metoprolol increased significantly mean R-R interval, R-R inter val total, and high-frequency variability at supine rest and barorefle x sensitivity, but ramipril did not significantly affect these variabl es. The metoprolol-induced decrease in ambulatory BP correlated with t he prolongation of the R-R interval and the increase of high-frequency variability at supine rest. The present data show that 4-week treatme nt with metoprolol increases tonic and reflex vagal cardiac activity, whereas ramipril does not affect vagal cardiac control in essential hy pertension. Increase in vagal activity may contribute to the BP-loweri ng effect of metoprolol in hypertensive patients. (C) 1998 American Jo urnal of Hypertension, Ltd.