ACE inhibition reduces left ventricular mass independent of pressure without affecting coronary flow and flow reserve in spontaneously hypertensive rats.

Abstract

Systemic and regional (including coronary) hemodynamics were studied in spontaneously hypertensive and normotensive Wistar Kyoto rats after 3 weeks of treatment with one of the three doses of the angiotensin converting enzyme inhibitor, ramipril. The effects of respective treatments on cardiovascular mass and systemic, coronary, and regional hemodynamics (at rest, during maximal treadmill exercise, and during dipyridamole infusion) then were evaluated in conscious rats using radiomicrosphere techniques. Low-dose ramipril (10 micrograms/kg/day by gavage) neither decreased arterial pressure nor reduced cardiac mass. However, medium (100 micrograms/kg/day) and high (1 mg/kg/day) doses reduced total cardiac and left ventricular masses to the same extent in spontaneously hypertensive rats, despite a much greater fall in arterial pressure with a high dose. Resting cardiac index, and myocardial and all other organ blood flows remained unchanged in both strains. When compared with Wistar Kyoto rats, coronary circulation was impaired in untreated spontaneously hypertensive rats (ie, reduced coronary flow and flow reserve and increased minimal coronary vascular resistance during dipyridamole infusion). This remained unchanged by ramipril. Furthermore, significant (and comparable) increases in cardiac index and myocardial blood flow and decreases in coronary vascular resistance were produced by maximal treadmill exercise in both strains. This also was unaffected by ramipril. These data showed that angiotensin converting enzyme inhibition with suboptimal and optimal hypotensive doses of ramipril reversed left ventricular hypertrophy in spontaneously hypertensive rats, but coronary flow, flow reserve, and minimal coronary vascular resistance remained unchanged despite left ventricular hypertrophy reversal.