The effect of nebivolol on the production of nitric oxide induced by bacterial lipopolysaccharide and peptidoglycan in mice

Nitric oxide (NO) plays a pivotal role in maintaining balance of physiological events in many systems including the autonomic, cardiovascular, hematological, and pulmonary systems. Lipopolysaccharide (LPS) and peptidoglycan (PGN), components of the outer cell membranes of Gram-negative bacteria and cell walls of Gram-positive bacteria respectively, are incriminated in NO-induced septic shock. Nebivolol is a third generation β1-adrenoceptor blocker with a vasodilatory property attributed to enhanced availability of nitric oxide and reduction of cellular oxidative stress through an unknown mechanism. The current study explored the hypothesis that if nebivolol enhances the availability of NO, pretreatment with nebivolol may enhance production of NO in response to subsequent treatment with LPS and PGN, an observation that may have relevance in clinical septic shock. Groups of female BALB/c mice each containing 12 mice (6-8 weeks old) were injected intraperitoneally with LPS (30 μg/mouse), PGN (100 μg/mouse), nebivolol (0.25 μg/g, 0.35 μg/g, 0.7 μg/g), LPS and nebivolol (0.25 μg/g), LPS and nebivolol (0.35 μg/g), LPS and nebivolol (0.7 μg/g), PGN and nebivolol (0.25 μg/g), PGN and nebivolol (0.35 μg/g). One group of mice was injected with saline and another served as control. Three mice from each group were bled 1, 3, 6 and 9 hours post-injection, the blood was pooled and the nitrite serum levels, reflecting NO concentration, were determined using Greiss reagent. The following results were obtained: 1) Treatment with saline did not induce NO production; 2) LPS induced NO production to a maximal limit of 545% at 9 hours as compared to treatment with saline; 3) PGN did not induce NO production; 4) Nebivolol at most doses and periods (7 out of 10 determinations) increased NO production over a range of 18-110% as compared to treatment with saline; 5) Nebivolol enhanced LPS-induced production of NO by 58% at a dose of 0.7 μg/gm at 9 hours. It is concluded that nebivolol induces NO production. At low doses nebivolol initially appeared to have a suppressive or no effect on NO production induced by LPS. Increase in the dose of nebivolol resulted in augmentation of LPS-induced production of NO. PGN, in the dose tested, did not have an effect on NO production.