Quinaprilat Increases Total Body Vascular Compliance in Rats with Myocardial Infarction

To test whether quinaprilat, a new angiotensin-converting enzyme (ACE) inhibitor, has any venous effect, we measured its immediate effects on mean circulatory filling pressure (MCFP), intravascular volume, and total body vascular (i.e., venous) compliance in conscious rats with healed myocardial infarction induced by coronary artery ligation. MCFP was determined by inflating a right atrial balloon to arrest the circulation instantly and temporarily. Total body vascular compliance was derived from total circulatory pressure–volume relationships as determined by series measurements of MCFP with different intravascular volume status. In 8 rats with mean infarct size of 26 ± 4%, 30-min infusion of quinaprilat (0.1 mg/kg/min) decreased both mean arterial and central venous pressures (MAP, CVP) by 8 and 0.7 mm Hg, respectively (p < 0.02); heart rate (HR), MCFP, hematocrit, and blood volume remained unchanged. As compared with control vehicle infusion, quinaprilat increased total body vascular compliance (2.09 ± 0.12 vs. 2.69 ± 0.23 ml/kg/mm Hg; p < 0.05) and decreased extrapolated unstressed circulating volume (34.96 ± 1.10 vs. 28.53 ± 2.55 ml/kg; p < 0.02). These data suggest that quinaprilat produces possible venodilation through improved total body vascular compliance, thereby reducing cardiac preload in this rat model of myocardial infarction.