Effects of low carbohydrate provision on isomyosin expression in the isoproterenol stressed rat heart

While previous findings suggest that increased carbohydrate (CHO) provision and/or utilization can be involved in the up regulation of V1 cardiac isomyosin expression in both the insulin deficient and the semi-starved rat, little is known about the role of CHO provision and/or utilization in regulating isomyosin expression in normal animals. This study was undertaken to ascertain whether a limited carbohydrate provision combined with repeated episodes of an increased cardiac energy demand can induce a down regulation of the V1 cardiac myosin inoenzyme in normal, young adult rats, i.e., a response similar to that seen in insulin deficient/food restricted rats. Animals were assigned to one of three major groups according to diet and/or drug treatment: (1) a mixed-diet control group; (2) a low-carbohydrate (LC)/high-fat-diet group; and (3) a low-carbohydrate-diet group treated with 3-mercaptopicolinic acid (MPA), an inhibitor of gluconeogenesis. In each of the above groups, subgroups of animals were metabolically challenged with daily isoproterenol injections (0.2 mg/kg/day) sufficient to markedly elevate cardiac work for at least 3 h. Four weeks of treatment reduced myofibrillar calcium activated ATPase activity by 17% (P less than 0.05) in the LC-diet-fed group treated with both isoproterenol and MPA. No change in myofibril ATPase was observed in any of the other experimental groups relative to the mixed diet control group. Isomyosin profile was not changed in any of the experimental groups. Tissue glycogen and plasma glucose and free fatty acid analyses provided indirect evidence of an increased utilization of fat for energy provision, especially in the low-carbohydrate-diet groups treated with MPA.(ABSTRACT TRUNCATED AT 250 WORDS)