Sex differences in myocardial oxygen and glucose metabolism

Background: Both physiologic and pathophysiologic conditions affect the myocardium's substrate use and, consequently, its structure, function, and adaptability. The effect of sex on myocardial oxygen, glucose, and fatty acid metabolism in humans is unknown. Methods and Results: We studied 25 young subjects (13 women and 12 men) using positron emission tomography, quantifying myocardial blood flow, myocardial oxygen consumption (MVO₂), and glucose and fatty acid extraction and metabolism. MVO₂ was higher in women than in men (5.74 ± 1.08 μmol · g^-1 · min^-1 vs 4.26 ± 0.69 μmol · g^-1 · min^-1, P < .005). Myocardial glucose extraction fraction and utilization were lower in women than in men (0.025 ± 0.019 vs 0.062 ± 0.028 [P < .001] and 133 ± 96 nmol · g^-1 · min^-1 vs 287 ± 164 nmol · g^-1 · min^-1 [P < .01], respectively). There were no sex differences in myocardial blood flow, fatty acid metabolism, or plasma glucose, fatty acid, or insulin levels. Female sex was an independent predictor of increased MVO₂ (P = .01) and decreased myocardial glucose extraction fraction and utilization (P < .005 and P < .05, respectively). Insulin sensitivity was an independent predictor of increased myocardial glucose extraction fraction and utilization (P < .01 and P = .01, respectively). Conclusions: Further studies are necessary to elucidate the mechanisms responsible for sex-associated differences in myocardial metabolism. However, the presence of such differences may provide a partial explanation for the observed sex-related differences in the prevalence and manifestation of a variety of cardiac disorders.