ANGIOTENSIN-II INCREASES LEFT-VENTRICULAR MASS WITHOUT AFFECTING MYOSIN ISOFORM MESSENGER-RNAS

We studied the effect of chronic (7 days) angiotensin II (Ang II) infu sion in nonpressor and presser doses on cardiovascular mass and expres sion of alpha- and beta-myosin heavy chain genes in the left ventricle in normotensive Wistar rats. An increased left ventricular mass was o bserved in rats receiving nonpressor and presser doses of Ang II, but only high doses increased arterial pressure. Normalization of arterial pressure during Ang II infusion by losartan, a specific Ang II recept or antagonist, or hydralazine had different effects on left ventricula r mass. Losartan prevented the increased left ventricular mass, and hy dralazine did not affect left ventricular mass. Northern blot analysis showed that the switch in left ventricular myosin isoform mRNA from t he adult to the fetal pattern occurred only in rats given the presser Ang II dose. Both losartan and hydralazine, in parallel with the norma lization of arterial pressure, prevented this myosin isoform switch. T hus, these data suggest that the Ang II-induced increase in left ventr icular mass was not dependent on pressure overload, but the switch in myosin isoform mRNA from the adult to the fetal pattern was dependent on pressure overload.