Effect of cyclic GMP reduction on regional myocardial mechanics and metabolism in experimental left ventricular hypertrophy

We tested the hypotheses that decreased myocardial cyclic GMP levels produced by intracoronary injection of methylene blue would increase local myocardial work and O-2 consumption while decreasing intracellular cyclic GMP and that the relation between work, O-2 consumption, and cyclic GMP may be altered in left ventricular hypertrophy (LVH) produced by aortic valve plication. In 8 control and 8 LVH open-chest anesthetized dogs, 1 mg/kg/min methylene blue was infused into the left anterior descending coronary artery (LAD); the circumflex region (CFX) served as control area. Regional work was calculated as the integrated product of force (miniature transducer) and segment shortening (sonomicrometry). Regional myocardial O-2 consumption was calculated from flow measurements (radioactive microspheres), and regional O-2 saturations (microspectrophotometry). A radioimmunoassay was used to determine intracellular level of cyclic GMP in the myocardium. Global hemodynamics and blood gases were unchanged by methylene blue in both control and LVH animals. Intracoronary methylene blue increased regional work from 762 +/- 129 to 1,451 +/- 307 g . mm/min in controls and from 912 +/- 173 to 1581 +/- 253 g . mmimin in the LVH groups. No significant changes in CFX regional work were observed. Regional blood flow, O-2 extraction, and O-2 consumption remained unchanged after injection of methylene blue in both control and LVH animals. The basal levels of cyclic GMP in the LVH group were fivefold higher than that in controls. In both groups, cyclic GMP levels were significantly decreased by methylene blue and to a greater extent in the LVH animals (from 6.16 +/- 1.2 to 3.34 +/- 0.44 pmol/g) than in the control animals (from 1.32 +/- 0.20 to 1.09 +/- 0.19 pmol/g). Therefore, intracoronary methylene blue increased regional myocardial work equally in control and LVH hearts without affecting regional metabolism (i.e., increased efficiency). For the same increased mechanical function, the hypertrophic myocardium exhibited a greater reduction in cyclic GMP pool size.