Chronic myocardial hypoxia increases nitric oxide synthase and decreases caveolin-3

Nitric oxide synthase (NOS) is believed to play an important role in protec ting the myocardium against ischemia. Chronic hypoxia from birth increases NOS activity in the myocardium resulting in enhanced nitric oxide productio n and increased resistance to ischemia. We examined the effects of chronic hypoxia on NOS gene and protein expression and on NOS protein association w ith caveolin-3. Rabbits were raised from birth in a normoxic (F1O2 = 0.21) or a hypoxic (F1O2 = 0.12) environment for 9 d, and then the hearts were is olated. Ribonuclease protection assays revealed that chronic hypoxia did no t alter NOS transcript levels for NOS1, NOS2, or NOS3. The most abundant tr anscript was NOS3. Western analysis revealed NOS3 was the only isoform dete cted. Immunoblots of NOS3 immunoprecipitates showed that chronic hypoxia in creases NOS3 protein by 2.0 +/- 0.1 -fold and decreases the amount of caveo lin-3 that can be coprecipitated with NOS3 by 5.5 +/- 0.9-fold. Immunoblots of normoxic and hypoxic hearts showed that chronic hypoxia decreases the a mount of caveolin-3 in heart homogenates by 2.2 +/- 0.5-fold. These data su ggest that a decrease in caveolin-3 plays a role in the mechanisms by which chronic hypoxia increases NOS3 activity in the myocardium. (C) 2000 Elsevi er Science Inc.