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-adrenergic vasoactivity in
chronically inflamed rat knee joints
McCaig Centre for Joint Injury & Arthritis Research, University of Calgary, Calgary, AB. T2N 4N1, Canada
It has previously been shown that chronic
inflammation causes a reduction in sympathetic nerve-mediated
vasoconstriction in rat knees. To determine whether this phenomenon is
due to an alteration in smooth muscle adrenoceptor function, the
present study compared the
-adrenoceptor profile of blood vessels
supplying the anteromedial capsule of normal and chronically inflamed
rat knee joints. While the rats were under urethan anesthesia, the
1-adrenoceptor agonists methoxamine and phenylephrine
and the
2-adrenoceptor agonist clonidine (0.1-ml bolus;
dose range 10
12-10
7 mol) were applied to
exposed normal rat knees, resulting in a dose-dependent fall in
capsular perfusion. Comparison of drug potencies indicated that
2-adrenergic effects >
1-vasoactivity. One week after intra-articular injection
of Freund's complete adjuvant to induce chronic joint inflammation,
the vasoconstrictor effects of methoxamine, phenylephrine, and
clonidine were all significantly attenuated compared with normal
controls. These findings show that the preponderance of sympathetic
adrenergic vasoconstriction in the anteromedial capsule of the rat is
carried out by postjunctional
2-adrenoceptors. Chronic
joint inflammation compromises
1- and
2-adrenoceptor function, and this change in
-adrenergic responsiveness may help explain the perfusion changes
commonly associated with inflammatory arthritis.
adjuvant monoarthritis; blood flow; sympathetic nervous system; laser Doppler perfusion imaging
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