Divergent biological actions of nitric oxide during progression of cardiac hypertrophy

Whether coronary endothelial nitric oxide synthase (eNOS) is up or down-regulated in left ventricular hypertrophy (LVH) and heart failure is controversial. Extrapolation of findings from purely molecular or biochemical assays of the NOS pathway to cardiac function may be problematic because of the multiple factors that potentially influence NO bioactivity. In this study, we investigated and correlated both the expression of eNOS protein and the biological activity of NO during the progression from compensated to decompensated LVH. Juvenile male guinea-pigs underwent supra-renal abdominal aortic banding or sham operation, and were studied either 3 weeks later (a stage of compensated LVH) or at 6-8 weeks (heart failure). Coronary vasodilator function was assessed in isolated Langendorff-perfused hearts from the responses to boluses of (1) bradykinin (0.001-10 μM) and substance P (0.01-10 μM), which release NO; (2) the NO donor, DEA-NO (0.1-1000 μM), (3) the NOS inhibitor, L-NMMA (10 mM). At 3 weeks, eNOS expression in whole LV by Western blot was similar in both groups (10.7 ± 0.5 vs 9.3 ± 0.7 arbitrary densitometric units; bands vs sham; n = 5 each). Immunocytochemistry revealed a similar localisation in both groups, ie, predominantly endothelial and capillary with little or no myocyte labelling. The maximum contraction to L-NMMA was significantly increased in bands compared to sham (17.8 ± 1.4 vs 6.2 ± 2.1%, n = 6 each; P<0.01), but agonist-induced and DEA-NO-induced vasodilation was similar in both groups. However, at 6-8 weeks, eNOS expression was significantly reduced in bands both by Western blot (band 7.8 ± 0.4 vs sham 12.2 ± 1.7 units, n = 5 each; P<0.05) and immunocytochemistry. At this time point, the response to L-NMMA was similar in bands and shams and there was also no significant difference in agonist-induced vasodilatation. These findings indicate that there is an increase in basal activity of nitric oxide in early compensated LVH, with a subsequent decrease during transition to heart failure. The relationship between molecular changes in eNOS protein expression and the biological activity of NO during LVH is complex, and varies with disease severity.