The Beta-1-Receptor Blocker Nebivolol Elicits Dilation of Cerebral Arteries by Reducing Smooth Muscle [Ca2+]i

The pretreatment of rats with nebivolol ameliorates bladder contractile dysfunction caused by ischemia-reperfusion injury

OBJECTIVE

The present study aimed to investigate the protective effect of nebivolol in the bladder isolated from rats exposed to ischemia-reperfusion (IR) injury.

METHODS

Sprague-Dawley rats were divided into control, IR, and nebivolol+IR groups. In the nebivolol+IR group, nebivolol was administered (0.4 mg/kg, subcutaneous) in rats prior to IR insult. At the end of the experimental protocol, the urinary bladder was rapidly isolated and bladder strips were mounted in an organ bath. After the equilibration period, potassium chloride (KCl, 20-100 mM) or carbachol (0.01-10 μM) was cumulatively added to the organ bath to generate cumulative concentration-response curves (CCRCs). Oxidative stress and interleukin 6 (IL-6) levels were also evaluated in the bladder tissue.

RESULTS

The CCRCs of KCl and carbachol were significantly reduced in the IR group compared to those of the control, and this inhibition was reversed by the pretreatment of rats with nebivolol (P < .05). The IR group's total antioxidant status was significantly lower with a concomitant increase in IL-6 levels than that of the control and nebivolol+IR groups (P < .05).

CONCLUSIONS

The present study indicates that pretreatment of rats with nebivolol (0.4 mg/kg) could improve bladder contractile dysfunction caused by IR injury through suppression of increased oxidative stress and IL-6 levels.

Metoprolol and Nebivolol Prevent the Decline of the Redox Status of Low-Molecular-Weight Aminothiols in Blood Plasma of Rats During Acute Cerebral Ischemia

Cerebral ischemia has previously been shown to cause a systemic decrease in levels of the reduced forms of low-molecular-weight aminothiols [cysteine (Cys), homocysteine (Hcy), and glutathione (GSH)] in blood plasma. In this study, we examined the effect of beta-adrenergic receptor (β-AR) antagonists metoprolol (Met) and nebivolol (Neb) on the redox status of these aminothiols during acute cerebral ischemia in rats. We used a model of global cerebral ischemia (bilateral occlusion of common carotid arteries with hypotension lasting for 10 minutes). The antagonists were injected 1 hour before surgery. Total and reduced Cys, Hcy, and GSH levels were measured 40 minutes after the start of reperfusion. Neb (0.4 and 4 mg/kg) and Met (8 and 40 mg/kg) treatment increased the levels of reduced aminothiols and the global methylation index in the hippocampus. The treatments also prevented any decrease in reduced aminothiol levels in blood plasma during ischemia. Although both of these drugs eliminated delayed postischemic hypoperfusion, only Neb reduced neuronal damage in the hippocampus. The results indicate an essential role of β1-AR blockage in the maintenance of redox homeostasis of aminothiols in the plasma and brain during acute cerebral ischemia.

Differential Free Intracellular Calcium Release by Class II Antiarrhythmics in Cancer Cell Lines

Class II antiarrhythmics or β-blockers are antisympathetic nervous system agents that act by blocking β-adrenoceptors. Despite their common clinical use, little is known about the effects of β-blockers on free intracellular calcium (Ca²⁺ _i), an important cytosolic second messenger and a key regulator of cell function. We investigated the role of four chemical analogs, commonly prescribed β-blockers (atenolol, metoprolol, propranolol, and sotalol), on Ca²⁺ _i release and whole-cell currents in mammalian cancer cells (PC3 prostate cancer and MCF7 breast cancer cell lines). We discovered that only propranolol activated free Ca²⁺ _i release with distinct kinetics, whereas atenolol, metoprolol, and sotalol did not. The propranolol-induced Ca²⁺ _i release was significantly inhibited by the chelation of extracellular calcium with ethylene glycol tetraacetic acid (EGTA) and by dantrolene, an inhibitor of the endoplasmic reticulum (ER) ryanodine receptor channels, and it was completely abolished by 2-aminoethoxydiphenyl borate, an inhibitor of the ER inositol-1,4,5-trisphosphate (IP₃) receptor channels. Exhaustion of ER stores with 4-chloro-m-cresol, a ryanodine receptor activator, or thapsigargin, a sarco/ER Ca²⁺ ATPase inhibitor, precluded the propranolol-induced Ca²⁺ _i release. Finally, preincubation of cells with sotalol or timolol, nonselective blockers of β-adrenoceptors, also reduced the Ca²⁺ _i release activated by propranolol. Our results show that different β-blockers have differential effects on whole-cell currents and free Ca²⁺ _i release and that propranolol activates store-operated Ca²⁺ _i release via a mechanism that involves calcium-induced calcium release and putative downstream transducers such as IP₃ The differential action of class II antiarrhythmics on Ca²⁺ _i release may have implications on the pharmacology of these drugs.