Methods: Seventy-five patients (43 males, 32 females; mean age 61.6±5.8 years; range 41 to 76 years) who were scheduled f or c oronary a rtery b ypass g rafting w ere enrolled in this study. Patients were assigned randomly to three groups. In group 1, 50 mg metoprolol, in group 2 5 mg nebivolol, and in group 3 90 mg diltiazem therapy was initiated five days before surgery. Samples of internal mammary artery were obtained intraoperatively. Nitric oxide synthase activity was measured by the quantitative sandwich enzyme-linked immunosorbent assay and graft free flow was calculated.

Results: The mean tissue nitric oxide synthase activity was found to be 0.4±0.0 U/mg in group 1, 2.4±0.3 U/mg in group 2 and 0.4±0.0 U/mg in group 3. There was a significant difference in the mean tissue nitric oxide synthase activity among the groups (p<0.05) with a higher rate in group 2. The mean graft free flow was significantly higher in group 2 compared to other groups (p<0.01).

Conclusion: Our study results suggest that preoperative nebivolol therapy increases tissue nitric oxide synthase concentration and graft free flow in the human internal mammary artery compared to metoprolol and diltiazem.