ACE-INHIBITION REDUCES LEFT-VENTRICULAR MASS-INDEPENDENT OF PRESSURE WITHOUT AFFECTING CORONARY FLOW AND FLOW RESERVE IN SPONTANEOUSLY HYPERTENSIVE RATS

Systemic and regional (including coronary) hemodynamics were studied i n spontaneously hypertensive and normotensive Wistar Kyoto rats after 3 weeks of treatment with one of the three doses of the angiotensin co nverting enzyme inhibitor, ramipril. The effects of respective treatme nts on cardiovascular mass and systemic, coronary, and regional hemody namics (at rest, during maximal treadmill exercise, and during dipyrid amole infusion) then were evaluated in conscious rats using radiomicro sphere techniques. Low-dose ramipril (10 mu g/kg/day by gavage) neithe r decreased arterial pressure nor reduced cardiac mass. However, mediu m (100 mu g/kg/day) and high (1 mg/kg/day) doses reduced total cardiac and left ventricular masses to the same extent in spontaneously hyper tensive rats, despite a much greater fall in arterial pressure with a high dose. Resting cardiac index, and myocardial and all other organ b lood hows remained unchanged in both strains. When compared with Wista r Kyoto rats, coronary circulation was impaired in untreated spontaneo usly hypertensive rats (ie, reduced coronary flow and flow reserve and increased minimal coronary vascular resistance during dipyridamole in fusion). This remained unchanged by ramipril. Furthermore, significant (and comparable) increases in cardiac index and myocardial blood how and decreases in coronary vascular resistance were produced by maximal treadmill exercise in both strains. This also was unaffected by ramip ril. These data showed that angiotensin converting enzyme inhibition w ith suboptimal and optimal hypotensive doses of ramipril reversed left ventricular hypertrophy in spontaneously hypertensive rats, but coron ary how, flow reserve, and minimal coronary vascular resistance remain ed unchanged despite left ventricular hypertrophy reversal.