Minoxidil-induced cardiac hypertrophy in guinea pigs

To investigate whether during cardiac hypertrophy changes occur in contract ile protein composition and in mechanical and energetic properties of the m yocardium, contractile protein composition, isometric force and adenosine t riphosphate (ATP) consumption were studied in control and hypertrophied gui nea-pig hearts. Cardiac hypertrophy was induced by adding minoxidil (120 or 200 mg/l) to the drinking water. Protein analysis was performed by one-dim ensional gel electrophoresis. The myosin heavy-chain (MHC) composition was determined in an enzyme-linked immunosorbent assay (ELISA). ATP consumption and force development were simultaneously measured during isometric contra ction in chemically skinned trabeculae. Histochemical analysis of cross-sec tional. area of cardiomyocytes and interstitial space was performed on the left ventricular tissue of 200 mg/l minoxidil-treated and control guinea pi gs. Minoxidil treatment (120 and 200 mg/l) significantly increased left ven tricular dry weight normalized for body weight by 19 +/- 4 and 24 +/- 4%, r espectively. No significant differences were found in the cellular cross-se ctional area, while interstitial space was slightly decreased in minoxidil- treated hearts. In left ventricular trabeculae of 200 mg/l minoxidil-treate d guinea pigs, ATPase activity was slightly less than in those of control g uinea pigs, whereas force did not differ significantly. Calcium sensitivity of force and ATPase activity were not affected by minoxidil treatment. Gel electrophoresis revealed no difference in contractile protein composition, but a tendency towards a lower amount of alpha-MHC in the minoxidil-treate d hearts was found in ELISA.