Abstract 12052: Role of eNOS and nNOS in Beta3-Adrenergic Receptor Mediated Cardioprotection
Background: The B3-adrenergic receptor (B3-AR), found in the endothelium and myocardium, has emerged as a potential target for the treatment of cardiovascular diseases including hypertension, acute MI, and heart failure. Previous studies indicate that B3-AR activation increases eNOS activity and subsequent nitric oxide (NO) bioavailability. B3-AR activation also modulates NO signaling via nNOS. We hypothesized that acute B3-AR agonist therapy would attenuate the severity of myocardial ischemia-reperfusion (MI-R) injury via B3-AR stimulation, eNOS and/or nNOS activation, and increased myocardial NO levels.
Methods: Mice (WT, B3-AR KO mice and eNOS−/−) were subjected to 45 min of MI in vivo followed by R for 24 hr. Nebivolol (NEB) (500 ng/kg), CL 316243 (CL) (1 μg/kg), BRL-37344 (BRL) (1 μg/kg), or saline vehicle (VEH) was administered via intracardiac injection at the time of R. At 24 hr of R, myocardial area-at-risk (AAR) per left ventricle (LV) and infarct size per area-at-risk (INF/AAR) were evaluated using Evan's Blue and TTC. Serum troponin-I levels were also measured. In separate studies, cardiac tissue and plasma samples were collected from mice treated with NEB or VEH following a single injection to evaluate eNOS phosphorylation (eNOS-P) status as well as the expression levels of eNOS, nNOS and iNOS. We also measured plasma nitrite and nitrosothiol levels.
Results: NEB treatment reduced INF/AAR by 37% (p < 0.001 vs. VEH) and serum troponin-I levels from 41±4 to 25±4 ng/mL (p < 0.05 vs. VEH). Administration of NEB very rapidly (i.e. 5–15 min) increased phosphorylation of the eNOS activation site, Ser-1177 (p < 0.001 vs. VEH) and a 2-fold increase (p < 0.05 vs. VEH) in myocardial nitrite and plasma nitrosothiol levels at 30 minutes. NEB also rapidly increased (2-fold) the expression of nNOS. There were no changes in total eNOS or iNOS protein levels. Treatment with CL and BRL reduced INF by 39% and 42% respectively (p < 0.001 vs. VEH). Nebivolol (500 ng/kg) failed to reduce INF size following MI-R in eNOS−/− mice and B3-AR KO mice.
Conclusions: Our results indicate that B3-AR stimulation by 3 chemically distinct agonists (NEB, CL and BRL) triggers rapid eNOS and nNOS activation and significantly protects against MI-R in the murine heart by an NO-dependent mechanism.
- Beta-adrenergic receptor agonists
- Nitric oxide synthase
- Endothelial function
- Nitric oxide
- Reperfusion injury
- © 2010 by American Heart Association, Inc.