Reduced cardiac functional reserve in apolipoprotein E knockout mice.

Several years ago, the authors reported that aortic flow velocity under resting conditions was significantly higher in apolipoprotein E knockout (apoE-KO) mice than in age-matched C57Black/6J wildtype (WT) controls. The goal of this study was to examine whether the cardiac functional reserve is impacted in response to a pharmacological stress agent in apoE-KO mice. Cardiac function was measured noninvasively by the Doppler ultrasound method at baseline and at 1 min, 5 min, 10 min, and 20 min after intraperitoneal injection of dobutamine at the doses of 1 microg/g, 3 microg/g, or 10 microg/g in 16-month-old male apoE-KO (n = 9) and WT (n = 10) mice under light anesthesia with 1.5% isoflurane via inhalation. The baseline peak and mean aortic flow velocities were 39% to 48% higher, and left ventricular contractility measured by peak acceleration rate of aortic flow velocity was 24% higher in apoE-KO compared with WT mice (P < 0.01). Dobutamine stress dose-dependently increased cardiac function, which, however, was significantly smaller with a right shift of the dose-response curve in apoE-KO mice compared with WT controls. The hypotensive response to dobutamine was not significantly different between the 2 groups. Thus, despite an elevated resting aortic flow velocity and left ventricular contractility, cardiac functional reserve in response to dobutamine stress was significantly reduced in apoE-KO mice, which could be the consequence of coronary atherosclerosis and endothelial dysfunction that limits blood supply to the heart.