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Vol. 289, Issue 2, 762-767, May 1999
Department of Pharmacology and Toxicology, Michigan State
University, East Lansing, Michigan
In the present study, endothelin (ET) agonists and receptor selective
antagonists were used to characterize ET receptors mediating constriction in guinea pig mesenteric veins (250-300 µm diameter) in
vitro. The contribution of ET-evoked vasodilator release to venous tone
was also explored. Computer-assisted video microscopy was used to
monitor vein diameter. Endothelin-1 (ET-1), endothelin-3 (ET-3), and
sarafotoxin 6c (S6c) produced sustained concentration-dependent contractions with a rank order agonist potency of ET-1 = S6c > ET-3. Indomethacin (1 µM) and
N
-nitro-L-arginine (100 µM) enhanced ET-1 and S6c responses. The ETA selective antagonists
BQ-610 (100 nM) and PD156707 (10 nM) shifted ET-1
concentration-response curves rightward and decreased maximal ET-1
responses, without changing S6c responses. The ETB
selective antagonist BQ-788 (100 nM) shifted S6c responses rightward
but produced no change in ET-1 responses. Combined application of
BQ-788 and BQ-610 or BQ-788 and PD 156707 produced a rightward shift in
ET-1 responses that was greater than shifts produced by BQ-610 or PD
156707 alone. In conclusion, smooth muscle in guinea pig mesenteric
veins expresses ETA and ETB receptors coupled
to contractile mechanisms. Activation of endothelial ETB
receptors results in release of vasodilators, primarily nitric oxide.
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