Carvedilol blockade of rat myocardial alpha1-adrenoceptors

Carvedilol binding to β2-adrenergic receptors inhibits CFTR-dependent anion secretion in airway epithelial cells

Carvedilol functions as a nonselective β-adrenergic receptor (AR)/α1-AR antagonist that is used for treatment of hypertension and heart failure. Carvedilol has been shown to function as an inverse agonist, inhibiting G protein activation while stimulating β-arrestin-dependent signaling and inducing receptor desensitization. In the present study, short-circuit current (Isc) measurements using human airway epithelial cells revealed that, unlike β-AR agonists, which increase Isc, carvedilol decreases basal and 8-(4-chlorophenylthio)adenosine 3',5'-cyclic monophosphate-stimulated current. The decrease in Isc resulted from inhibition of the cystic fibrosis transmembrane conductance regulator (CFTR). The carvedilol effect was abolished by pretreatment with the β2-AR antagonist ICI-118551, but not the β1-AR antagonist atenolol or the α1-AR antagonist prazosin, indicating that its inhibitory effect on Isc was mediated through interactions with apical β2-ARs. However, the carvedilol effect was blocked by pretreatment with the microtubule-disrupting compound nocodazole. Furthermore, immunocytochemistry experiments and measurements of apical CFTR expression by Western blot analysis of biotinylated membranes revealed a decrease in the level of CFTR protein in monolayers treated with carvedilol but no significant change in monolayers treated with epinephrine. These results demonstrate that carvedilol binding to apical β2-ARs inhibited CFTR current and transepithelial anion secretion by a mechanism involving a decrease in channel expression in the apical membrane.

Carvedilol ameliorates endothelial dysfunction in streptozotocin-induced diabetic rats

The beta-blocker, carvedilol has an additional endothelium-dependent vasodilating properties in patients with hypertension or heart failure. Whether carvedilol can improve endothelium-dependent relaxation in a diabetic animal model and its mechanism of action are unknown. The aim of this study was to investigate the effect of carvedilol on the endothelial-response of aortas from diabetic rats and the underlying mechanism. Acetylcholine-induced endothelium-dependent relaxation, sodium nitroprusside (SNP)-induced endothelium-independent relaxation, and expression of nitric oxide synthase 3 (NOS3) mRNA were measured in aortas isolated from both non-diabetic and streptozotocin-induced diabetic rats. The level of NO in serum was also measured 5 weeks after carvedilol administration (1 or 10 mg/kg/day). Endothelium-dependent relaxation declined along with the decrease of serum NO level in aortas from diabetic rats. Treatment with carvedilol for 5 weeks prevented the inhibition of endothelium-dependent relaxation and the decrease of serum NO levels caused by diabetes. The expression of NOS3 mRNA, protein expression and NOS3 phosphorylation at Ser1177 in diabetic rat aorta was very low in untreated diabetic aortas compared with the healthy group. Administration of carvedilol not only significantly increased the expression of NOS3 mRNA but also protein expression and NOS3 phosphorylation at Ser1177 in the healthy and diabetic groups. In conclusion, chronic carvedilol administration significantly ameliorated the endothelial dysfunction in diabetic rat aortas, in which increased NO level, up-regulated NOS3 mRNA and phosphorylation at Ser1177 may be involved.

Carvedilol blockade of alpha1- and beta-adrenoceptor induced inotropic responses in rats with congestive heart failure

Carvedilol is a combined alpha(1)- and beta-adrenoceptor antagonist. We investigated the ability of carvedilol to antagonize functional effects mediated through myocardial alpha(1)-adrenoceptors in failing vs. non-failing (sham-operated) control hearts and compared such antagonisms to those of myocardial beta-adrenoceptors. Congestive heart failure was induced in Wistar rats by coronary artery ligation. Papillary muscles experiments were performed. Carvedilol antagonized inotropic effects mediated through myocardial alpha(1)-adrenoceptors with similar potencies in failing (pK(i)=7.7 (95%, CI; 7.4-8.0)) and sham-operated hearts (pK(i)=7.9 (95%, CI; 7.6-8.1)). The potency for the alpha(1)-adrenoceptors was 10-30-fold lower than that for the beta-adrenoceptors. In failing hearts, the alpha(1)-adrenoceptor mediated response was similar in size to the attenuated beta-adrenoceptor mediated inotropic response. The beta-adrenoceptor mediated lusitropic effects were not, however, attenuated in failing compared to sham-operated hearts. A low degree of alpha(1)-adrenoceptor blockade in the myocardium may contribute to the beneficial effects of carvedilol in heart failure.