Gao Y S, Vanhoutte P M
Department of Physiology and Biophysics, Mayo Clinic, Rochester, Minnesota 55905.
Am J Physiol. 1989 Nov;257(5 Pt 1):C1034-7. doi: 10.1152/ajpcell.1989.257.5.C1034.
This study was designed to investigate whether the respiratory epithelium can modulate the tone of the underlying smooth muscle in response to decreases in partial pressure of O2 (PO2). Canine bronchial segments with or without epithelium (diameter, 4-6 mm; length, 50-60 mm) were mounted in organ chambers and perfused intraluminally with modified Krebs-Ringer bicarbonate solution [temperature, 37 degrees C; PO2 varying from 600 (control) to 40 mmHg; PCO2, 36 mmHg]. Isometric tension was recorded by means of stirrups passed through the wall of the central part of the bronchial segment. During contractions to carbachol, the tissues with epithelium showed epithelium-dependent relaxations when the PO2 was decreased. The level of relaxation was dependent on the PO2. The epithelium-dependent relaxation could not be blocked by the following agents: indomethacin, methylene blue, propranolol, or tetrodotoxin (antagonists or blockers of cyclooxygenase, guanylate cyclase, beta-adrenoceptors, and sodium channels, respectively). The epithelium-dependent relaxation was not accompanied by the release of an assayable relaxing factor in the bronchial lumen. The experiments suggest that 1) lowering the PO2 induces the epithelium to release a relaxing factor(s), which is neither a product of cyclooxygenase nor endothelium-derived relaxing factor; 2) a local reflex mechanism is not involved in the phenomenon; and 3) the relaxing factor(s) either is not released into the bronchial lumen or, if it is, is catalyzed rapidly in the lumen on release.
本研究旨在调查呼吸上皮是否能响应氧分压（PO2）降低来调节其下方平滑肌的张力。将有或无上皮的犬支气管段（直径4 - 6毫米；长度50 - 60毫米）安装在器官腔室中，并通过支气管段中央部分的壁穿入镫形物记录等长张力，管腔内灌注改良的 Krebs - Ringer 碳酸氢盐溶液（温度37℃；PO2 从600（对照）变化至40 mmHg；PCO2 36 mmHg）。在对卡巴胆碱的收缩过程中，当PO2降低时，有上皮的组织表现出依赖上皮的舒张。舒张程度取决于PO2。依赖上皮的舒张不能被以下药物阻断：吲哚美辛、亚甲蓝、普萘洛尔或河豚毒素（分别为环氧化酶、鸟苷酸环化酶、β - 肾上腺素能受体和钠通道的拮抗剂或阻滞剂）。依赖上皮的舒张在支气管腔内未伴随可检测到的舒张因子释放。这些实验表明：1）降低PO2诱导上皮释放一种舒张因子，其既不是环氧化酶产物也不是内皮源性舒张因子；2）该现象不涉及局部反射机制；3）舒张因子要么未释放到支气管腔内，要么即使释放了，在释放时也会在腔内迅速被催化。
