Abstract
BACKGROUND AND PURPOSE: Sympathetic nervous system (SNS) hyperactivity is characteristic of chronic heart failure (HF) and significantly worsens prognosis. The success of β-adrenoceptor antagonist (β-blockers) therapy in HF is primarily attributed to protection of the heart from the noxious effects of augmented catecholamine levels. β-Blockers have been shown to reduce SNS hyperactivity in HF, but the underlying molecular mechanisms are not understood. The GPCR kinase-2 (GRK2)-α(2) adrenoceptor-catecholamine production axis is up-regulated in the adrenal medulla during HF causing α(2) -adrenoceptor dysfunction and elevated catecholamine levels. Here, we sought to investigate if β-blocker treatment in HF could lower SNS activation by directly altering adrenal GRK2 levels. EXPERIMENTAL APPROACH: Four weeks after myocardial infarction-induced HF, adult rats were randomized to 10-week treatment with vehicle (HF/C) or bisoprolol (HF/B). Cardiac function and dimensions were measured. In heart and adrenal gland, GRK2 levels were assessed by RT-PCR and Western blotting and adrenoceptors studied with radioligand binding. Catecholamines and α(2) adrenoceptors in adrenal medulla chromaffin cell cultures were also measured. KEY RESULTS: Bisoprolol treatment ameliorated HF-related adverse cardiac remodelling and reduced plasma catecholamine levels, compared with HF/C rats. Bisoprolol also attenuated adrenal GRK2 overexpression as observed in HF/C rats and increased α(2) adrenoceptor density. In cultures of adrenal medulla chromaffin cells from all study groups, bisoprolol reversed HF-related α(2) adrenoceptor dysfunction. This effect was reversed by GRK2 overexpression. CONCLUSION AND IMPLICATIONS: Blockade of β-adrenoceptors normalized the adrenal α(2) adrenoceptor-catecholamine production axis by reducing GRK2 levels. This effect may contribute significantly to the decrease of HF-related sympathetic overdrive by β-blockers.