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Departments of 1 Veterinary Biomedical Sciences and 2 Veterinary Medicine and Surgery, University of Missouri, Columbia, Missouri 65211
We
hypothesized that pulmonary arteries (PA) from identical branch orders
within left and right caudal lung lobes would exhibit similar vasomotor
responses. Arterial rings from caudal lung lobes of female swine were
examined in vitro. Vascular smooth muscle contraction to KCl and
norepinephrine did not differ. Vascular relaxation to
endothelium-dependent (bradykinin, acetylcholine, A-23187) and
-independent (sodium nitroprusside, zero-calcium Krebs solution)
vasodilators was assessed. Right PA exhibited less maximal
relaxation to acetylcholine (50%) than did left PA (69%; P < 0.001). Maximal relaxation to sodium nitroprusside did not differ,
although right PA had a lower drug concentration resulting in
half-maximal relaxation (6.26 × 10
8
M) than did left PA (9.57 × 10
8 M; P < 0.05). Nitric oxide synthase inhibition with an
arginine analog (N
-nitro-L-arginine
methyl ester) depressed acetylcholine-induced relaxation but the left
vs. right difference persisted. Indomethacin enhanced relaxation to
acetylcholine and abolished the difference between left and right. We
conclude that endothelium-dependent vasorelaxation is less in porcine
right than in left PA because of greater release of one or more
constricting prostanoids in arteries from the right caudal lobe.
pulmonary circulation; arachidonic acid metabolites; porcine; endothelial cell function; blood flow distribution
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