Objective--Coronary microvessels are functionally coupled to the myocardial metabolic state. In hypercholesterolemia, the coronary vascular dysfunction extends to microvascular levels. We hypothesized that the vasodilator signal transduction from ischemic heart is impaired in the coronary microvascular wall of hypercholesterolemia.

Methods and Results--Rabbits were fed with normal chow (control group) or 2% high-cholesterol diet (hypercholesterolemia group) for 8 weeks. Coronary microvessels isolated from rabbit hearts were pressurized and gently placed on a beating canine heart. Myocardial ischemia was produced in the beating heart and the diameter of the isolated microvessel was observed using an intravital microscope with a floating objective. In control group, the isolated microvessels significantly dilated 2 minutes after the onset of ischemia, and a plateau was observed at 10 minutes. In contrast, the microvessels from hypercholesterolemia group did not dilate during ischemia. Dihydroethidium fluorescence microscopy revealed an elevated superoxide level in the microvessels of hypercholesterolemia group. The application of tiron (free radical scavenger) significantly dilated the isolated microvessels only from hypercholesterolemic animals.

Conclusions--We conclude that the transduction of vasodilator signals derived from ischemic myocardium is impaired in the coronary microvascular wall of hypercholesterolemia. Enhanced oxidative stress in hypercholesterolemia may alter the microvascular function.