EFFECTS OF LONG-TERM COCAINE ADMINISTRATION AND EXERCISE ON CARDIAC METABOLISM AND ISOMYOSIN EXPRESSION

Although chronic cocaine use is cardiotoxic, its use remains problemat ic in athletics. Hence adaptive changes induced in the heart by superi mposing chronic cocaine use on an exercise training are of interest bu t remain poorly understood. Therefore this study investigated the effe cts of cocaine treatment combined with exercise training on the metabo lic and contractile properties of the heart. Male Sprague-Dawley rats were assigned to one of four groups: normal sedentary (NS, n = 6), coc aine sedentary (CS, n = 6), normal trained (NT, n =6), and cocaine tra ined (CT, n = 6). Trained animals were sprint trained 4 times/week. CS and CT animals received cocaine (25 mg/kg, ip) 6 times/week, 15 min b efore each exercise bout and 2 additional times per week. After 12 wee ks, all animals were sacrificed, and the hearts were removed and analy zed for citrate synthase activity, 3-hydroxyacyl-CoA dehydrogenase act ivity, Ca2+-activated myofibrillar ATPase activity, and myosin isoform distribution. None of the groups demonstrated altered cardiac metabol ic properties, but cocaine alone and in conjunction with exercise redu ced myofibrillar ATPase activity (p < 0.05) and increased expression o f the low ATPase myosin isoform, V3. These data suggest that the poten tial of the citric acid cycle and beta-oxidation is not sensitive to c hronic cocaine treatment, but the distribution of cardiac myosin among its three isoforms is affected. Furthermore, high-intensity treadmill training does not interact with cocaine to further alter these proper ties.