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1 Department of Physiology and Pharmacology, Wake Forest University School of Medicine, Winston-Salem, North Carolina 27157-1083; and 2 Institute of Human Physiology and Clinical Experimental Research, Semmelweis University, Budapest, Hungary 1082
Insulin resistance (IR)
impairs vascular responses in peripheral arteries. However, the effects
of IR on cerebrovascular control mechanisms are completely unexplored.
We examined the vascular function of isolated middle cerebral arteries
(MCAs) from fructose-fed IR and control rats. Endothelium-dependent
vasodilation elicited by bradykinin (BK) was reduced in IR compared
with control MCAs. Maximal dilation to BK (10
6 M) was
38 ± 3% (n = 13) in control and 19 ± 3%
(n = 10) in IR arteries (P < 0.01).
N
-nitro-L-arginine methyl ester
(L-NAME; 10 µM) decreased responses to BK in control
arteries by ~65% and inhibited the already reduced responses
completely in IR MCAs. Indomethacin (10 µM) reduced relaxation to BK
in control MCAs by ~40% but was largely ineffective in IR arteries.
Combined L-NAME and indomethacin treatments eliminated the
BK-induced dilation in both groups. Similarly to BK,
endothelium-mediated and mainly cyclooxygenase (COX)-dependent dilation
to calcium ionophore A23187 was reduced in IR arteries compared with
controls. In contrast, vascular relaxation to sodium nitroprusside was
similar between the IR and control groups. These findings demonstrate that endothelium-dependent dilation in cerebral arteries is impaired in
IR primarily because of a defect of the COX-mediated pathways. In
contrast, nitric oxide-mediated dilation remains intact in IR arteries.
middle cerebral artery; bradykinin; A23187; nitric oxide; cyclooxygenase
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