Skeletal muscle beta-adrenoreceptors and phosphate metabolism abnormalities in heart failure in rats

To investigate the mechanisms leading to skeletal muscle metabolic abnormalities in chronic heart failure (CHF), we studied phosphate metabolism and skeletal muscle beta-adrenoreceptors (beta-AR) in rats 12-14 wk after coronary ligation (CL). We performed 31P magnetic resonance spectroscopy in the gastrocnemius muscle during motor activity produced by electrical stimulation (5 Hz). The initial slope of phosphocreatine (PCr) depletion was higher in the CL rats compared with sham-operated rats (Pi/PCr/time: 0.211 +/- 0.045 vs. 0.113 +/- 0.029; P < 0.05). During recovery, both PCr resynthesis rate and maximal rate of oxidative ATP synthesis were reduced threefold in the CL rats compared with controls (11 +/- 2 vs. 37 +/- 7 mmol.l-1.min-1, P < 0.04; and 20 +/- 3 vs. 79 +/- 18 mmol.l-1.min-1, P < 0.03, respectively). There were no significant differences either for the skeletal muscle density (13 +/- 6 vs. 15 +/- 3 fM/mg) or for the affinity (0.244 +/- 0.149 vs. 0.246 +/- 0.146 nM) of beta-AR between the two groups. This study showed that, although in moderate CHF skeletal muscle metabolic abnormalities can be demonstrated, these changes could not be explained by skeletal muscle beta-adrenergic receptor alterations in this experimental model.