Increased Monoamine Oxidase Activity during the Development of Cardiac Hypertrophy in the Rat

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Abstract
In rats, the increase in heart mass during normal growth is accompanied by a marked increase in the concentration of monamine oxidase (MAO). Similarly, cardiac hypertrophy resulting from experimental hypertension (induced either by desoxycorticosterone acetate (DOCA) and sodium or by renal artery stenosis) is also associated with a pronounced increase in MAO concentration. Conversely, the delayed growth of the heart occurring during sodium restriction is accompanied by a lower MAO activity. These changes in MAO, independent of the cause, appear closely related to the mass of the heart. However, the reduction in norepinephrine storage observed in the heart and other tissues of rats made hypertensive with DOCA and sodium cannot be explained by the changes in the concentration of MAO. The MAO activity of other tissues of the hypertensive rats is similar to that in the tissues of normal rats, with the exception of the kidney in which the MAO concentration is reduced. The subcellular distribution of MAO is similar in hypertensive and control rats. In both groups, the MAO is mainly localized in the mitochondrial fraction of the liver. In contrast, in the heart, the major fraction of MAO activity is found in the microsomal fraction.