Rhaleb N E, Carretero O A
Hypertension and Vascular Research Division, Henry Ford Hospital, Detroit, Michigan 48202.
Life Sci. 1994;55(17):1351-63. doi: 10.1016/0024-3205(94)00768-3.
Bradykinin (BK) and its analogues induce a typical biphasic response (relaxation followed by contraction) in the isolated rat duodenum. We studied the role of B1 and B2 BK receptors and nitric oxide (NO) in relaxation and contraction of the isolated rat duodenum. Both effects are concentration-dependent: BK has shown an EC50 (contraction) of 3.8 +/- 1.9 x 10(-7) M and an IC50 (relaxation) of 3.0 +/- 0.7 x 10(-9). Similar results were obtained with the selective B2 receptor agonists [Hyp3,Tyr(Me)8]-BK and [Phe8 psi (CH2-NH)Arg9]-BK, showing an EC50 of 9.6 +/- 1.9 x 10(-7) M and 5.6 +/- 2.9 x 10(-7) M and an IC50 of 3.5 +/- 0.6 x 10(-10) M and 6.8 +/- 1.7 x 10(-10) M, respectively. Furthermore, the effects induced by these three agonists were not altered when tissues were treated with 42.1 microM Mergetpa, a carboxypeptidase N inhibitor. While the relaxant and contractile effects elicited by BK were significantly inhibited in the presence of Hoe 140 (0.7 microM), a selective B2 receptor antagonist, those induced by the selective B1 receptor agonist desArg9-BK were not. Furthermore, [Leu8]-desArg9-BK (2.6 microM), which is both a pure and selective B1 receptor antagonist, acted as an agonist on the rat duodenum, inducing a biphasic relaxant and contractile effect. These relaxant and contractile effects were not altered by drugs that inhibit or stimulate NO production, such as L-NAME (200 microM), a combination of L-NAME (200 microM) and indomethacin (2.5 microM), L-arginine (1 mM), or superoxide dismutase (20 U/ml). However, the contractile effect was significantly reduced when tissues were preincubated with methylene blue (100 microM), which inhibits activation of guanylate cyclase. We conclude that 1) BK and its analogues selectively activate a B2 receptor, producing a biphasic effect (relaxation and contraction); 2) DesArg9-BK may either acts via a different receptor which might be another B1 receptor subtype or a typical B1 receptor where [Leu8]-desArg9-BK acts as a partial agonist; and 3) neither NO nor the prostaglandin pathway mediates BK-induced relaxation in the isolated rat duodenum.
缓激肽（BK）及其类似物可在离体大鼠十二指肠中诱导出典型的双相反应（先舒张后收缩）。我们研究了B1和B2缓激肽受体以及一氧化氮（NO）在离体大鼠十二指肠舒张和收缩中的作用。两种效应均呈浓度依赖性：BK的收缩半数有效浓度（EC50）为3.8±1.9×10⁻⁷ M，舒张半数抑制浓度（IC50）为3.0±0.7×10⁻⁹。选择性B2受体激动剂[Hyp3,Tyr(Me)8]-BK和[Phe8 psi (CH2-NH)Arg9]-BK也得到了类似结果，其EC50分别为9.6±1.9×10⁻⁷ M和5.6±2.9×10⁻⁷ M，IC50分别为3.5±0.6×10⁻¹⁰ M和6.8±1.7×10⁻¹⁰ M。此外，当用42.1微摩尔/升的羧肽酶N抑制剂Mergetpa处理组织时，这三种激动剂所诱导的效应未发生改变。虽然在存在选择性B2受体拮抗剂Hoe 140（0.7微摩尔/升）的情况下，BK所引发的舒张和收缩效应均被显著抑制，但选择性B1受体激动剂去精氨酸9-缓激肽（desArg9-BK）所诱导的效应却未被抑制。此外，既是纯的又是选择性B1受体拮抗剂的[亮氨酸8]-去精氨酸9-缓激肽（2.6微摩尔/升）在大鼠十二指肠上表现为激动剂，诱导出双相的舒张和收缩效应。这些舒张和收缩效应不受抑制或刺激NO生成的药物影响，如N⁻硝基-L-精氨酸甲酯（L-NAME，200微摩尔/升）、L-NAME（200微摩尔/升）与吲哚美辛（2.5微摩尔/升）的组合、L-精氨酸（1毫摩尔/升）或超氧化物歧化酶（20单位/毫升）。然而，当组织用亚甲蓝（100微摩尔/升）预孵育时，收缩效应显著降低，亚甲蓝可抑制鸟苷酸环化酶的激活。我们得出以下结论：1）BK及其类似物选择性激活B2受体，产生双相效应（舒张和收缩）；2）去精氨酸9-缓激肽可能通过不同受体起作用，该受体可能是另一种B1受体亚型，或者是[亮氨酸8]-去精氨酸9-缓激肽作为部分激动剂作用的典型B1受体；3）在离体大鼠十二指肠中，NO和前列腺素途径均不介导BK诱导的舒张。
