Russell J A
Department of Pediatrics, State University of New York, Buffalo 14214.
Respir Physiol. 1987 Oct;70(1):25-35. doi: 10.1016/s0034-5687(87)80029-4.
The presence of inhibitory presynaptic alpha-2 adrenergic receptors and their ability to modulate nerve-mediated relaxation responses was examined in strips of canine tracheal smooth muscle (TSM). TSM strips were incubated with 3H-labelled norepinephrine (NE), rinsed, and mounted in superfusion chambers for electrical stimulation (ES) of the intramural adrenergic neurons. Yohimbine, an alpha-2 receptor antagonist, increased the release of [3H]NE into the superfusate during ES and decreased the amount of [3H]NE remaining in TSM strips after ES, indicating the presence of presynaptic alpha-2 receptors. Whether these alpha-2 receptors were functional in atropine-treated TSM was determined by comparing the inhibitory effect of ES on TSM contractions induced by histamine in the absence and presence of yohimbine. Relaxation of TSM strips at stimulus frequencies of 1-20 Hz was significantly greater in the presence of yohimbine. Moreover, the stimulus frequency required to produce a 50% relaxation, was 5.1 +/- 0.9 Hz in control strips, but only 2.1 +/- 0.4 in TSM strips pretreated with yohimbine. We conclude that presynaptic alpha-2 receptors serve a functional role in regulating NE release in canine TSM.
在犬气管平滑肌（TSM）条带中检测了抑制性突触前α-2肾上腺素能受体的存在及其调节神经介导的舒张反应的能力。将TSM条带与3H标记的去甲肾上腺素（NE）孵育，冲洗后，安装在用于对壁内肾上腺素能神经元进行电刺激（ES）的灌流室中。α-2受体拮抗剂育亨宾在电刺激期间增加了[3H]NE向灌流液中的释放，并减少了电刺激后TSM条带中剩余的[3H]NE量，表明存在突触前α-2受体。通过比较在不存在和存在育亨宾的情况下电刺激对组胺诱导的TSM收缩的抑制作用，来确定这些α-2受体在阿托品处理的TSM中是否具有功能。在育亨宾存在的情况下，TSM条带在1-20Hz刺激频率下的舒张明显更大。此外，产生50%舒张所需的刺激频率，在对照条带中为5.1±0.9Hz，但在用育亨宾预处理的TSM条带中仅为2.1±0.4Hz。我们得出结论，突触前α-2受体在调节犬TSM中NE释放方面发挥功能性作用。
