Altered contractile response due to increased β3- adrenoceptor stimulation in diabetic cardiomyopathy: The role of nitric oxide synthase 1-derived nitric oxide

Background: In the diabetic heart, the positive inotropic response to (3-adrenoceptor stimulation is altered and β 1 and β 2 adrenoceptors are down-regulated, whereas β 3 adrenoceptor is up-regulated. In heart failure, β 3 -adrenoceptor stimulation induces a negative inotropic effect that results from endothelial nitric oxide synthase (NOS3)-derived nitric oxide production. The objective of our study was to investigate the role of β 3 -adrenoceptor in diabetic cardiomyopathy. Methods: β-Adrenergic responses were investigated in vivo (dobutamine echocardiography) and in vitro (left ventricular papillary muscle) in healthy and streptozotocin-induced diabetic rats. The effect of β 3 -adrenoceptor inhibition on the inotropic response was studied in vitro. Immunoblots and NOS activities were performed in heart homogenates (electron paramagnetic resonance) and isolated cardiomyocytes. Data are mean percentage of baseline ± SD. Results: The impaired positive inotropic effect was confirmed in diabetes both in vivo (121 ± 15% vs. 160 ± 16%;P < 0.05) and in vitro (112 ± 5% vs. 179 ± 15%; P < 0.05). In healthy rat, the positive inotropic effect was not significantly modified in presence of β 3 -adrenoceptor antagonist (174 ± 20%), nonselective NOS inhibitor (N G -nitro-L-arginine methylester [L-NAME]; 183 ± 19%), or selective NOS1 inhibitor (vinyl-L-N-5-(1-ιmino-3-butenyl)-L-omithine [L-VNIO]; 172 ± 13%). In diabetes, in parallel with the increase in β 3 -adrenoceptor protein expression, the positive inotropic effect was partially restored by '33-adrenoceptor antagonist (137 ± 8%; P < 0.05), L-NAME (133 ± 11%; P < 0.05), or L-VNIO (130 ± 13%; P < 0.05). Nitric oxide was exclusively produced by NOS1 within diabetic cardiomyocytes. NOS2 and NOS3 proteins were undetectable. Conclusions: β 3 -Adrenoceptor is involved in altered positive inotropic response to β-adrenoceptor stimulation in diabetic cardiomyopathy. This effect is mediated by NOS1-derived nitric oxide in diabetic cardiomyocyte.