de Godoy Márcio A F, de Oliveira Ana Maria, Rattan Satish
Department of Medicine, Division of Gastroenterology & Hepatology, Jefferson Medical College, Thomas Jefferson University, 1025 Walnut Street, Room # 901 College, Philadelphia, PA 19107, USA.
J Pharmacol Exp Ther. 2004 Oct;311(1):394-401. doi: 10.1124/jpet.104.069856. Epub 2004 Jun 3.
We evaluated the role of receptor desensitization, activation of AT(2) receptors, and enzymatic degradation of angiotensin II (Ang II) by amino/neutral endopeptidases in rat anococcygeus smooth muscle (ASM) relaxation. Ang II (0.3 nM to 10 microM) produced contractions (E(max) = 21.50 +/- 5.73%) followed by passive relaxations (E(max) reduced to 9.08 +/- 2.55%). Contractions were inhibited (E(max) = 13.67 +/- 2.03%) by losartan (0.1 microM; AT(1) antagonist) but not by PD123,319 [S-(+)-1-([4-(dimethylamino)-3-methylphenyl]methyl)-5-(diphenylacetyl)-4,5,6,7-tetrahydro-1H-imidazo(4,5-c)pyridine-6-carboxylic acid] (0.1 microM; AT(2) antagonist). Conversely, the passive relaxation was inhibited (E(max) = 18.00 +/- 3.45%) by PD123,319 but not by losartan. Ang II (0.3 microM to 100 microM) produced initial contractions (E(max) = 11.49 +/- 9.39%) followed by active relaxations [I(max) (maximum inhibition elicited by the agonist) = 47.85 +/- 4.23%] on strips precontracted by bethanechol (100 microM). A second administration of Ang II on the background of bethanechol (1 h later) resulted in stronger relaxations (I(max) = 64.03 +/- 5.47%) without the initial contractions. N(G)-Nitro-l-arginine methyl ester [nitric-oxide synthase (NOS) inhibitor], ODQ (1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one; guanylate cyclase inhibitor), PD123,319, and tetrodotoxin (neurotoxin) inhibited the relaxations. The presence of AT(1) and AT(2) receptors was confirmed by Western blot. Experiments with amastatin (1 microM) and thiorphan (1 microM), aminopeptidase, and neutral endopeptidase inhibitors, respectively, excluded the involvement of enzymatic degradation in Ang II-induced relaxation of ASM. In conclusion, the rat ASM relaxation by Ang II is the result of active and passive relaxations. The passive relaxation depends on desensitization of excitatory AT(1) receptors, and the active relaxation is mediated by stimulation of AT(2) receptors and activation of the neuronal NOS/soluble guanylate cyclase pathway.
我们评估了受体脱敏、AT(2)受体激活以及氨基/中性内肽酶对血管紧张素II（Ang II）的酶促降解在大鼠肛门尾骨肌平滑肌（ASM）舒张中的作用。Ang II（0.3 nM至10 μM）引起收缩（E(max)=21.50±5.73%），随后是被动舒张（E(max)降至9.08±2.55%）。氯沙坦（0.1 μM；AT(1)拮抗剂）可抑制收缩（E(max)=13.67±2.03%），而PD123,319 [S-(+)-1-([4-(二甲氨基)-3-甲基苯基]甲基)-5-(二苯基乙酰基)-4,5,6,7-四氢-1H-咪唑并(4,5-c)吡啶-6-羧酸]（0.1 μM；AT(2)拮抗剂）则不能。相反，PD123,319可抑制被动舒张（E(max)=18.00±3.45%），而氯沙坦则不能。Ang II（0.3 μM至100 μM）在由氨甲酰甲胆碱（100 μM）预收缩的肌条上引起初始收缩（E(max)=11.49±9.39%），随后是主动舒张[I(max)（激动剂引起的最大抑制）=47.85±4.23%]。在氨甲酰甲胆碱存在的背景下（1小时后）再次给予Ang II会导致更强的舒张（I(max)=64.03±5.47%）且无初始收缩。N(G)-硝基-L-精氨酸甲酯[一氧化氮合酶（NOS）抑制剂]、ODQ（1H-[1,2,4]恶二唑并[4,3-a]喹喔啉-1-酮；鸟苷酸环化酶抑制剂）、PD123,319和河豚毒素（神经毒素）可抑制舒张。通过蛋白质印迹法证实了AT(1)和AT(2)受体的存在。分别用阿马astatin（1 μM）和硫磷酰胺（1 μM）进行的实验，即氨肽酶和中性内肽酶抑制剂，排除了酶促降解在Ang II诱导的ASM舒张中的作用。总之，Ang II引起的大鼠ASM舒张是主动舒张和被动舒张的结果。被动舒张取决于兴奋性AT(1)受体的脱敏，而主动舒张是由AT(2)受体的刺激和神经元NOS/可溶性鸟苷酸环化酶途径的激活介导的。
