Effect of adrenaline on myocardial oxygen consumption during selective and non-selective beta-adrenoceptor blockade comparison of atenolol and pindolol

Effect of obesity and insulin resistance on myocardial substrate metabolism and efficiency in young women

BACKGROUND

Obesity is a risk factor for impaired cardiac performance, particularly in women. Animal studies suggest that alterations in myocardial fatty acid metabolism and efficiency in obesity can cause decreased cardiac performance. In the present study, we tested the hypothesis that myocardial fatty acid metabolism and efficiency are abnormal in obese women.

METHODS AND RESULTS

We studied 31 young women (body mass index [BMI] 19 to 52 kg/m2); 19 were obese (BMI >30 kg/m2). Myocardial oxygen consumption (MVO2) and fatty acid uptake (MFAUp), utilization (MFAU), and oxidation (MFAO) were quantified by positron emission tomography. Cardiac work was measured by echocardiography, and efficiency was calculated as work/MVO2. BMI correlated with MVO2 (r=0.58, P=0.0006), MFAUp (r=0.42, P<0.05), and efficiency (r=-0.40, P<0.05). Insulin resistance, quantified by the glucose area under the curve (AUC) during an oral glucose tolerance test, correlated with MFAUp (r=0.55, P<0.005), MFAU (r=0.62, P<0.001), and MFAO (r=0.58, P<0.005). A multivariate, stepwise regression analysis showed that BMI was the only independent predictor of MVO2 and efficiency (P=0.0005 and P<0.05, respectively). Glucose AUC was the only independent predictor of MFAUp, MFAU, and MFAO (P<0.05, <0.005, and <0.005, respectively).

CONCLUSIONS

In young women, obesity is a significant predictor of increased MVO2 and decreased efficiency, and insulin resistance is a robust predictor of MFAUp, MFAU, and MFAO. This increase in fatty acid metabolism and decrease in efficiency is concordant with observations made in experimental models of obesity. These metabolic changes may play a role in the pathogenesis of decreased cardiac performance in obese women.

Effects of atenolol and pindolol on the hypokalaemic and cardiovascular responses to adrenaline infusion

To investigate if the intrinsic sympathomimetic activity of pindolol could modify its beta-blocking effects on the responses to an adrenaline infusion, 10 healthy volunteers were studied. At an interval of 1-4 weeks each subject received pindolol and atenolol in randomized order before the infusion of adrenaline 0.06 microgram.kg-1.min-1. Pindolol prevented hypokalaemia and significantly decreased the heart rate during the adrenaline infusion. These effects were not observed after atenolol. The diastolic blood pressure was slightly increased during the infusion of adrenaline after pindolol, whereas it remained unchanged after atenolol.