Verleden G M, Pype J L, Deneffe G, Demedts M G
Laboratory of Pneumology, Pulmonary Pharmacology Unit, Onderwijs en Navorsing.
Thorax. 1994 Jul;49(7):657-63. doi: 10.1136/thx.49.7.657.
Frusemide can inhibit various indirectly acting bronchoconstrictor stimuli in asthmatic patients. Both frusemide and bumetanide also modulate airway neurotransmission in some species but there are no data on the effect of loop diuretics on neurotransmission in man. An in vitro study was performed in human airways to investigate the possible neuromodulatory action of two loop diuretics, frusemide and bumetanide, and to elucidate whether a cyclooxygenase inhibitor such as indomethacin could modulate the effect of frusemide. The effect of acetazolamide, a carbonic anhydrase inhibitor, was also investigated.
Electrical field stimulation (EFS; 40 V, 0.5 ms, 0.5-32 Hz for 15 seconds) in human airways with or without epithelium was used to induce a cholinergic contraction (n = 5 in all experiments). Indomethacin was present throughout. After obtaining a control frequency-response curve, different concentrations of diuretic were added to the organ bath and another frequency-response curve was constructed. To determine whether the effect of the diuretic was prejunctional or postjunctional a cumulative concentration-response curve to exogenous acetylcholine (Ach, 0.3 mumol/l to 10 mmol/l) was constructed in the presence of a diuretic (frusemide 1 mmol/l or bumetanide 0.1 mmol/l) or its vehicle. In some experiments indomethacin was omitted from the organ bath to investigate the possible involvement of cyclooxygenase products.
Both frusemide (10 mumol/l to 1 mmol/l) and bumetanide (1 mumol/l to 0.1 mmol/l) produced a concentration-dependent inhibition of the EFS-induced cholinergic contraction in human airways in vitro but only in epithelium denuded tissues. Frusemide (1 mmol/l) produced a maximum inhibition of 46.3% (SE 9.9%) at 0.5 Hz and bumetanide (0.1 mmol/l 39.6 (6.2)% at 0.5 Hz. Without indomethacin in the organ bath the frusemide-induced inhibition was enhanced at 4, 8, and 16 Hz, but bumetanide-induced inhibition was not enhanced at any frequency when indomethacin was omitted. Frusemide (1 mmol/l) and bumetanide (0.1 mmol/l) had no effect on the cumulative concentration-response curve to exogenous Ach (0.3 mumol/l to 10 mmol/l). Acetazolamide (100 mumol/l) had no effect on the EFS-induced cholinergic contraction in tissues with or without epithelium.
In human airways in vitro both frusemide and bumetanide produced a concentration-dependent inhibition of the EFS-induced cholinergic contraction. This inhibition is mediated through a prejunctional mechanism. Epithelium removal was necessary to achieve this effect. The mechanism of action of frusemide and bumetanide on airway nerves remains unclear: inhibition of the Na-K-Cl cotransporter is a possibility and, for frusemide, release of endogenous cyclooxygenase products may be involved. Carbonic anhydrase inhibition, on the other hand, is unlikely to be a factor.
速尿可抑制哮喘患者多种间接作用的支气管收缩刺激。速尿和布美他尼在某些物种中也可调节气道神经传递，但关于袢利尿剂对人体神经传递的影响尚无数据。进行了一项人体气道的体外研究，以探讨两种袢利尿剂速尿和布美他尼可能的神经调节作用，并阐明吲哚美辛等环氧化酶抑制剂是否能调节速尿的作用。还研究了碳酸酐酶抑制剂乙酰唑胺的作用。
在有或无上皮的人体气道中进行电场刺激（EFS；40V，0.5ms，0.5 - 32Hz，持续15秒）以诱导胆碱能收缩（所有实验n = 5）。全程加入吲哚美辛。获得对照频率 - 反应曲线后，将不同浓度的利尿剂加入器官浴中并构建另一条频率 - 反应曲线。为确定利尿剂的作用是在节前还是节后，在存在利尿剂（速尿1mmol/L或布美他尼0.1mmol/L）或其溶媒的情况下构建对外源性乙酰胆碱（Ach，0.3μmol/L至10mmol/L）的累积浓度 - 反应曲线。在一些实验中，从器官浴中省略吲哚美辛以研究环氧化酶产物可能的参与情况。
速尿（10μmol/L至1mmol/L）和布美他尼（1μmol/L至0.1mmol/L）在体外人体气道中均产生浓度依赖性抑制EFS诱导的胆碱能收缩，但仅在去上皮组织中。速尿（1mmol/L）在0.5Hz时产生的最大抑制为46.3%（标准误9.9%），布美他尼（0.1mmol/L）在0.5Hz时为39.6（6.2）%。当器官浴中没有吲哚美辛时，速尿诱导的抑制在4、8和16Hz时增强，但当省略吲哚美辛时，布美他尼诱导的抑制在任何频率下均未增强。速尿（1mmol/L）和布美他尼（0.1mmol/L）对外源性Ach（0.3μmol/L至10mmol/L）的累积浓度 - 反应曲线无影响。乙酰唑胺（100μmol/L）对有或无上皮的组织中EFS诱导的胆碱能收缩均无影响。
在体外人体气道中，速尿和布美他尼均产生浓度依赖性抑制EFS诱导的胆碱能收缩。这种抑制是通过节前机制介导的。去除上皮是实现此效应所必需的。速尿和布美他尼对气道神经的作用机制仍不清楚：抑制钠 - 钾 - 氯共转运体是一种可能性，对于速尿，可能涉及内源性环氧化酶产物的释放。另一方面，碳酸酐酶抑制不太可能是一个因素。
