Rydningen H T, Omland T, Opstad P K, Helle K B
Acta Physiol Scand. 1987 Aug;130(4):601-7. doi: 10.1111/j.1748-1716.1987.tb08182.x.
The relative importance of VIP in reduction of vascular tone was studied in circular and longitudinal preparations of the VIP-innervated rat portal vein. Exogenous VIP inhibited the methoxamine-evoked contractures in the atropine-blocked preparations with a lower potency in the inner, circular (pD2 = 6.4 +/- 0.5, n = 6) than in the outer, longitudinal layer (pD2 = 7.7 +/- 0.1, n = 6). VIP was also a less efficient relaxant (intrinsic activity (alpha) = 0.60 +/- 0.16, n = 6) of the inner than of the outer layer (alpha = 1.00). The selective (salbutamol) and the non-selective (isoproterenol) beta 2-agonists completely relaxed the methoxamine contractures in both layers and the potency (isoproterenol) was higher in the inner (pD2 = 6.39 +/- 0.32, n = 6) than in the outer layer (pD2 = 5.67 +/- 0.34, n = 6). Plasma from the portal-mesenteric vein of anaesthetized, fasting rats contained 0.036 nM VIP (median, n = 17), that is, several orders of magnitude lower than the range of VIP concentrations relaxing the methoxamine contracted vein preparations via VIP receptors of the apamin-blockable category. The results support the hypothesis that alpha 1-adrenoceptor-induced contractions in the circular layer are predominately relaxed via beta 2-adrenoceptors while relaxation of the outer layer may occur via VIP receptors, probably activated by local release of the neuropeptide.
在由血管活性肠肽（VIP）支配的大鼠门静脉的环形和纵形标本中，研究了VIP在降低血管张力方面的相对重要性。外源性VIP在阿托品阻断的标本中可抑制甲氧明诱发的挛缩，其在内层环形标本中的效力较低（pD2 = 6.4 ± 0.5，n = 6），低于外层纵形标本（pD2 = 7.7 ± 0.1，n = 6）。VIP对内层的舒张作用也比外层低效（内在活性（α） = 0.60 ± 0.16，n = 6）（外层α = 1.00）。选择性β2 - 激动剂（沙丁胺醇）和非选择性β2 - 激动剂（异丙肾上腺素）均可使两层标本中的甲氧明挛缩完全舒张，且异丙肾上腺素在内层的效力更高（pD2 = 6.39 ± 0.32，n = 6），高于外层（pD2 = 5.67 ± 0.34，n = 6）。麻醉禁食大鼠的门静脉 - 肠系膜静脉血浆中含有0.036 nM的VIP（中位数，n = 17），即比通过阿帕明可阻断类VIP受体使甲氧明收缩的静脉标本舒张的VIP浓度范围低几个数量级。这些结果支持以下假设：环形层中α1 - 肾上腺素能受体诱导的收缩主要通过β2 - 肾上腺素能受体舒张，而外层的舒张可能通过VIP受体发生，可能是由神经肽的局部释放激活。
