An intracardiac production of
aldosterone has been recently reported in rat. This production is increased both acutely and chronically by
angiotensin II, observations suggesting that the heart contains a steroidogenic system that is regulated similarly to the adrenal one. Cardiac production of
aldosterone is small compared with that of the adrenal, raising the question of its function in normal conditions. Moreover, the regulation of this synthesis in pathophysiologic states remains unknown. In an analysis of the effects of a one-month
myocardial infarction (MI) on the cardiac steroidogenic system, it was observed that
aldosterone-synthase mRNA and the
aldosterone concentration were increased by 2- and 3.5-fold, respectively, in the noninfarcted part of the rat left ventricle. MI also induced a 1. 9-fold increase in the cardiac
angiotensin II level.
Losartan prevented these changes, and the MI-induced
collagen deposition in noninfarcted area of the left ventricle was reduced by 1.6- and 2. 5-fold by both
spironolactone and
losartan treatments, respectively. Thus, these observations indicate that MI is associated with tissue-specific activation of myocardial
aldosterone synthesis. This activation is mediated by cardiac
angiotensin II via the
angiotensin II type 1 (AT1) receptor, and the resultant increase of intracardiac
aldosterone level may be involved in post-MI
ventricular remodeling.