Lack of evidence for peripheral alpha1- adrenoceptor blockade during long-term treatment of heart failure with carvedilol

OBJECTIVES The purpose of this study was to determine whether carvedilol’s alpha1-adrenoceptor antagonism persists during long-term therapy of patients with congestive heart failure (CHF). BACKGROUND Carvedilol and metoprolol differ in that carvedilol also antagonizes beta2- and alpha1-adrenoceptors. We hypothesized that in contrast to metoprolol, carvedilol would increase calf vascular conductance (CVC), blunt neurally mediated vasoconstriction and attenuate neuroeffector transfer function gain. METHODS We randomized 36 patients with CHF (age 55 ± 1 years, ejection fraction 19 ± 1%, means ± SE) to either drug. Blood pressure (BP), heart rate, muscle sympathetic nerve activity (MSNA) and CVC were assessed before and after four months of treatment. The variability of BP and MSNA was determined using fast Fourier transformation. RESULTS Paired data were obtained in 23 (carvedilol, 13; metoprolol, 10) subjects. Both beta-blockers decreased heart rate, but neither affected mean BP or CVC (carvedilol: 0.016 ± 0.002 to 0.018 ± 0.003 U; metoprolol: 0.020 ± 0.002 to 0.020 ± 0.004 U). Isometric handgrip exercise (30% of maximum) increased heart rate, mean BP and MSNA. The calf vasoconstrictor response to handgrip exercise was not affected by carvedilol (from 16 ± 6 resistance U to 25 ± 10 resistance U, NS). The gain of the transfer of oscillations in MSNA into BP under resting conditions was not attenuated by carvedilol. CONCLUSIONS Carvedilol did not increase CVC, blunt the calf vasoconstrictor response to handgrip or attenuate the gain of the neuroeffector transfer function, indicating the absence of functionally important peripheral alpha1-adrenoceptor antagonism during long-term treatment of CHF.