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alpha2‐Adrenoreceptors contribute to norepinephrine‐induced constriction of mesenteric veins
Author(s) -
Hlavacova Alexandra
Publication year - 2006
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fasebj.20.4.a662-c
Subject(s) - yohimbine , phenylephrine , constriction , mesenteric arteries , agonist , medicine , stimulation , norepinephrine , endocrinology , vasoconstriction , antagonist , chemistry , mesenteric vein , vascular smooth muscle , prazosin , receptor , artery , smooth muscle , blood pressure , portal vein , dopamine
Mesenteric veins are more sensitive to stimulation by norepinephrine (NE) than arteries. Furthermore, veins desensitize more slowly than arteries in response to continuous stimulation by NE. These differences might be related to expression of functional α 2 adrenergic receptors (α 2 ARs) in venous smooth muscle cells. These studies investigated the contribution of α 2 ARs to NE induced constriction of murine mesenteric veins in vitro . Phenylephrine (PE) and NE caused concentration dependent (1 – 1000 nM) constrictions of mesenteric veins. The α 2 AR agonist, UK14304 (10‐1000 nM) did not cause venous constriction. However, yohimbine (300 nM), an α 2 AR blocker produced a 5‐fold rightward shift of the NE dose‐response curve in veins, but not arteries (EC 50 = 0.015 vs 0.08μM for NE and NE + yohimbine, respectively). BRL44408 (100 nM α 2A AR antagonist) or imiloxan (1 μM, α 2B antagonist) did change significantly NE dose‐response curves in veins. In contrast, MK912 (10nM, α 2C AR antagonist) produced a 4‐fold rightward shift (EC 50 s:0.01 vs 0.04 for NE and NE + MK912, respectively). This shift was comparable to the effect produced by yohimbine (300 nM). These data indicate that α 2 AR agonists do not directly constrict mesenteric veins; however, they contribute to constriction caused by the αAR non‐selective agonist NE. These data also indicate that the main α 2 AR subtype mediating the actions of NE in murine mesenteric veins is the α 2C AR.