EFFECTS OF ACE-INHIBITION AND BETA-BLOCKADE ON SKELETAL-MUSCLE FIBER TYPES IN DOGS WITH MODERATE HEART-FAILURE

The proportion of slow-twitch, fatigue-resistant type I skeletal muscl e (SM) fibers is often reduced in heart failure (HF), while the propor tion of fatigue-sensitive type-II fibers increases. This maladaptation may be partially responsible for the exercise intolerance that charac terize HF. In this study, we examined the effects of early monotherapy with the angiotensin-converting enzyme inhibor, enalapril, and the be ta-blocker, metoprolol, on SM fiber type composition in 18 dogs with m oderate HF produced by intracoronary microembolizations. HF dogs were randomized to 3 mo therapy with enalpril (10 mg twice daily), metoprol (25 mg twice daily), or no treatment. Triceps muscle biopsies were ob tained at baseline, before randomization, and at the end of 30 mo of t herapy. Type I and type II SM fibers were differentiated by myofibrill ar adenosinetriphosphatase (pH 9.4). In untreated dogs, the proportion of type I fibers was 27 +/- 1% before randomization and decreased to 23 +/- 1% (P < 0.05) at the end of 3 mo of follow up. In dogs treated with enalapril or metoprolol, the proportion of type I fibers was 30 /- 4 and 28 +/- 2% before randomization and 33 +/- 4 and 33 +/- 1%, re spectively after 3 mo of therapy. In conclusion, in dogs with moderate HF, early therapy with enalapril or metoprolol prevents the progressi ve decline in the proportion of type I SM fibers.