Abstract:  

The aim of this study was to evaluate the effect of NG-nitro-L-arginine methyl ester and thyroxine on the distribution of cardiac myosin heavy chains in mice. Myocardial hypertrophy was induced in mice by intraperitoneal injection with L-thyroxine and oral administration of NG-nitro-L-arginine methyl ester (L-NAME). Mice were randomly allocated into five groups: control, high and low doses of thyroxine and L-NAME. Heart weight divided by body weight was calculated and used as indicator for cardiac hypertrophy. Myosin heavy chains (MHCs) were separated using 4 % polyacrylamide gel electrophoresis. Hypertrophy was induced in mice treated with thyroxine and a high dose of L-NAME and was accompanied by a shift toward ?-MHC in thyroxine-treated mice and ?-MHC in L-NAME-treated mice. There was no difference with respect to MHC between a low dose of LNAME and a high dose; however, low doses of L-NAME did not result in cardiac hypertrophy. In conclusion, L-NAME treatment changes the MHC distribution from ?- toward ?- MHC and this transition in the MHCs occurs before heart hypertrophy. Further investigations are needed to determine whether L-NAME treatment causes this transition via a direct or indirect effect on the heart muscles.