SEVERE MYOCARDIAL INFARCTION DIMINISHES AEROBIC CAPACITY OF RAT SKELETAL MUSCLE 364

Abstract

Studies of heart failure in humans and rats have demonstrated that alterations in skeletal muscle metabolism and aerobic capacity occur. The purpose of this study was to determine whether myocardial infarction-induced alterations in skeletal muscle enzyme activities are generalized in muscles or are specific to muscles composed primarily of a given fiber type. The activity of several enzymes involved in glycolysis (phosphofructokinase [PFK] and lactate dehydrogenase [LDH]), terminal oxidation (citrate synthase [CS] and malate dehydrogenase [MDH]) and β-oxidation of fatty acids (3-hydroxyacyl CoA dehydrogenase [HADH]) were measured in soleus (S; type I fibers), plantaris (P; mixed fiber type), and the deep red (GR; type I and IIA fibers), middle (GM; mixed fiber type) and superficial white(GW; type IIB fibers) portions of gastrocnemius muscles from female Wistar rats. The animals were divided into three groups: shamoperated controls(n=13) and rats with moderate (45 ± 2%; n=10) and large (59 ± 4%; n=7) myocardial infarcts (MI). MI were surgically induced by ligating the left main coronary artery and after 2 months resulted in increases (P<0.05) in left ventricular end diastolic pressure (sham 5 ± 1 mmHg; moderate MI 11 ± 1; large MI 25 ± 1). Neither PFK nor LDH was different in either MI group compared to controls. Additionally, moderately sized MI induced little change in any of the enzyme activities. However, in rats with large MI, CS was lower in S (sham 24 ± 1μmol·min-1·g wet wt-1; large MI 18 ± 1), GR (sham 37 ± 2; large MI 31 ± 1) and GW (sham 8± 2; large MI 6 ± 1); MDH was lower in GR (sham 779± 2 μmol·min-1·g wet wt-1; large MI 656± 37) and GW (sham 210 ± 2; large MI 171 ± 4); and HADH was lower in P (sham 12 ± 1 μmol·min-1·g wet wt-1; large MI 9 ± 1) and GR (sham 17 ± 1; large MI 12 ± 1). These data indicate that reductions in aerobic capacity associated with heart failure occur in skeletal muscle regardless of fiber composition, and changes in enzyme activities appear to occur when severe heart failure is present.