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An indirect influence of phenylephrine on the release of endothelium‐derived vasodilators in rat small mesenteric artery
Author(s) -
Dora K A,
Hinton J M,
Walker S D,
Garland C J
Publication year - 2000
Publication title -
british journal of pharmacology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.432
H-Index - 211
eISSN - 1476-5381
pISSN - 0007-1188
DOI - 10.1038/sj.bjp.0703052
Subject(s) - phenylephrine , apamin , iberiotoxin , charybdotoxin , contraction (grammar) , mesenteric arteries , vasodilation , endothelium , medicine , endocrinology , chemistry , muscle contraction , artery , potassium channel , blood pressure
The possibility that stimulation of smooth muscle α 1 ‐adrenoceptors modulates contraction via the endothelium was examined in rat small mesenteric arteries. N ω ‐nitro‐ L ‐arginine methyl ester, ( L ‐NAME, 100 μ M to inhibit NO synthase) increased contraction to single concentrations of phenylephrine (1–3 μ M ) by approximately 2 fold (from a control level of 14.2±3.0 to 34.1±4.2% of the maximum contraction of the artery, n =20). The action of L ‐NAME was abolished by disrupting the endothelium. The subsequent addition of apamin (to inhibit small conductance Ca 2+ ‐activated K + channels, 50 n M ) further augmented phenylephrine contractions, in an endothelium‐dependent manner, to more than 3 fold above control (50.4±5.3% of the maximum contraction, n =11). Charybdotoxin (non‐selective inhibitor of large conductance Ca 2+ ‐activated K + channels, BK Ca , 50 n M ) plus L ‐NAME augmented the level of phenylephrine contraction to 4–5‐fold above control (64.1±3.1%, n =5), but this effect was independent of the endothelium. The potentiation of contraction by charybdotoxin could be mimicked with the selective BK Ca inhibitor, iberiotoxin,. Apamin together with L ‐NAME and charybdotoxin further significantly increased the phenylephrine contraction by 5–6‐fold, to 79.9±3.5% of the maximum contraction of the artery ( n =13). Phenylephrine failed directly to increase the intracellular Ca 2+ concentration in endothelial cells freshly isolated from the small mesenteric artery. Stimulation of smooth muscle α 1 ‐adrenoceptors in the mesenteric artery induces contraction that is markedly suppressed by the endothelium. The attenuation of contraction appears to reflect both the release of NO from the endothelium and the efflux of K + from both endothelial and smooth muscle cells. This suggests that the release of NO and endothelium‐derived hyperpolarizing factor can be evoked indirectly by agents which act only on the smooth muscle cells.British Journal of Pharmacology (2000) 129 , 381–387; doi: 10.1038/sj.bjp.0703052