ABSTRACT
Nitric oxide (NO) plays a pivotal role in main- taining balance of physiological events in many systems including the autonomic, cardiovas- cular, 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 in- criminated in NO-induced septic shock. Ne- bivolol is a third generation β1- adrenoceptor blocker with a vasodilatory property attributed to enhanced availability of nitric oxide and re- duction of cellular oxidative stress through an unknown mechanism. The current study ex- plored the hypothesis that if nebivolol enhances the availability of NO, pretreatment with ne- bivolol may enhance production of NO in re- sponse 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 (0.35µg/g). One group of mice was injected with saline and an- other served as control. Three mice from each group were bled 1, 3, 6 and 9 hours post-injec- tion, the blood was pooled and the nitrite serum levels, reflecting NO concentration, were de- termined 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 deter- minations) 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 in- duces NO production. At low doses nebivolol initially appeared to have a suppressive or no effect on NO production induced by LPS. In- crease 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.