Correlation of Myosin Heavy Chain Expression in the Rat with cAMP in Different Models of Hypertension-induced Cardiac Hypertrophy

Both genetically determined and artificially-induced hypertension lead to cardiac hypertrophy and shift the myosin heavy chain (MHC) expression to the β-MHC form. The cause of this change in gene expression is unknown. To contribute to the understanding of this phenomenon, we correlated the MHC expression in the left ventricle with basal, Forskolin- and isoprenaline-stimulated adenylate cyclase activity (cAMP production of membrane fractions). We used two control rat strains [Wistar-Hagemann (WH), Wistar-Kyoto (WKY)] and several rat models of hypertension; one clip-one kidney (1C-1K), desoxycorticosterone-treated rats (DOCA), rats with reduced renal mass (RRM) and spontaneously hypertensive rats (SHR). The level of hypertension correlated positively with the degree of cardiac hypertrophy (P < 0.01) and negatively (P < 0.05) with cAMP production, e.g. the higher the degree of hypertension, the lower both basal and stimulated cAMP levels. In addition we found that the lower the basal, isoprenaline- and Forskolin-stimulated cAMP production the lower was the expression of the α-MHC isoenzyme (P < 0.05). Thus, our data suggest that the decreased α-MHC expression upon hypertension-induced cardiac hypertrophy could be mediated via decreased adenylate cyclase activity and thus decreased intracellular cAMP production.