Abstract

Inflammation reduces pharmacological response to β1-blockers by down-regulating the target receptor protein. This may contribute to the sub-optimal response to pharmacotherapy with β-blockers. Nebivolol is a third generation β-adrenoceptor (AR) blocker with high selectivity for blocking β1 and β3-agonistitic properties. We studied whether response to nebivolol is also reduced by inflammation. Male Sprague-Dawley rats (Inflamed; Mycobacterium butyricum induced) and Control (healthy) were orally administered single doses of 2 mg/kg nebivolol (n=5) or 25 mg/kg propranolol (positive control, n=7-8); ECG recorded for PR and RR interval measurements; serial blood samples were collected for pharmacokinetic assessment. Subsequently, the myocardial β1, β2 and β3-AR levels were measured in homogenized hearts. For propranolol, inflammation resulted in increased concentration but reduced response and down-regulation of β1- AR. The action and disposition of nebivolol were, however, unaffected by inflammation despite the reduced β1-AR levels. The levels of β2 and β3-AR were unaffected by inflammation. The consistency of response to nebivolol despite inflammation may be due to the predominance of contribution of β2 and β3-AR. The lack of an inhibitory effect of inflammation on the clearance of nebivolol is suggestive of mechanisms other than an efficient hepatic metabolism for its low bioavailability. If extrapolated to human, nebivolol may be a more effective cardiovascular drug when inflammatory conditions are present.

Keywords: Inflammation, β-adrenoceptor, β3-adrenoceptor, β-blockers, arthritis, receptor downregulation, reduced response, PR interval, RR interval.