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Department of Internal Medicine and Cardiovascular Center, University of Iowa College of Medicine and Veterans Affairs Medical Center, Iowa City, Iowa 52242
Previous studies
showed that nitric oxide (NO) plays an important role in coronary
arteriolar dilation to increases in myocardial oxygen consumption
(M
O2). We sought to evaluate coronary
microvascular responses to endothelium-dependent and to
endothelium-independent vasodilators in an in vivo model.
Microvascular diameters were measured using intravital
microscopy in 10 normal (N) and 9 hyperglycemic (HG; 1 wk alloxan,
60 mg/kg iv) dogs during suffusion of acetylcholine (1, 10, and 100 µM) or nitroprusside (1, 10, and 100 µM) to test the effects on
endothelium-dependent and -independent dilation. During administration
of acetylcholine, coronary arteriolar dilation was impaired in HG, but
was normal during administration of nitroprusside. To examine a
physiologically important vasomotor response, 10 N and 7 HG control, 5 HG and 5 N during superoxide dismutase (SOD), and 5 HG and 4 N after
SQ29,548 (SQ; thromboxane A2/prostaglandin H2
receptor antagonist) dogs were studied at three levels of
MO2: at rest, during dobutamine (DOB; 10 µg · kg
1 · min1 iv), and during
DOB with rapid atrial pacing (RAP; 280 ± 10 beats/min). During
dobutamine, coronary arterioles dilated similarly in all groups, and
the increase in MO2 was similar among
the groups. However, during the greater metabolic stimulus (DOB+RAP),
coronary arterioles in N dilated (36 ± 4% change from diameter
at rest) significantly more than HG (16 ± 3%, P < 0.05). In HG+SQ and in HG+SOD, coronary arterioles dilated similarly
to N, and greater than HG (P < 0.05).
MO2 during DOB+RAP was similar among
groups. Normal dogs treated with SOD and SQ29,548 were not different
from untreated N dogs. Thus, in HG dogs, dilation of coronary
arterioles is selectively impaired in response to administration of the
endothelium-dependent vasodilator acetylcholine and during increases
in MO2.
coronary microcirculation; diabetes; dobutamine; superoxide; SQ29,548; superoxide dismutase
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