肺迷走C纖維神經參與發炎 引發大鼠呼吸道過度敏感之角色

Role of Pulmonary Vagal C-fibers in Inflammation-induced Airway Hypersensitivity in Rats

許諄諄(Chun-Chun Hsu)

指導教授 ： 林佑穗

臺北醫學大學/醫學院/醫學科學研究所/博士(2013年)

摘要

呼吸道過度敏感，是指對於相同程度的刺激物，卻引發較劇烈反應的現象。這現象可由肺發炎所致，也是呼吸道發炎疾病患者(例如：氣喘)的主要症狀。越來越多文獻顯示，肺迷走C纖維神經在肺發炎引發的呼吸道過度敏感形成中，扮演重要的角色。然而，此感覺神經參與的機轉，仍不清楚。刺激肺迷走C纖維可以引發多種呼吸反應，包括：呼吸暫停、咳嗽、呼吸道收縮和痰液分泌，這些反應是經由兩種神經反射途徑而來：中樞神經型反射以及局部軸突反射；局部軸突反射則是藉由肺迷走C纖維神經末梢釋放快肽所導致。本論文的研究主旨是要探討：當呼吸道發炎時，如何增強經由肺迷走C纖維神經所引發的中樞及局部軸突兩種反射，而表現出呼吸道過度敏感的現象。
研究一：探討呼吸道暴露於一種新發炎性介質─硫化氫，如何增強肺迷走C纖維神經引發的呼吸暫停反應(一種經由肺迷走C纖維神經引發的中樞神經型反射)。在麻醉、自發呼吸的Sprague-Dawley大鼠，吸入硫氫化鈉(一種硫化氫予體)霧氣，並不會改變基礎呼吸型態。然而，刺激肺迷走C纖維神經引發的呼吸暫停，在吸入硫氫化鈉後卻被增強。此增強作用，可被HC-030031 (一種TRPA1受器拮抗劑)的前處理完全抑制。另外，在迷走神經周圍辣椒素的處理後(選擇性阻斷迷走C纖維神經的傳導)，硫氫化鈉增強的呼吸暫停也消失，說明了迷走C纖維神經的重要性。為了進一步探討硫化氫對肺迷走C纖維神經的作用，以麻醉、用人工呼吸器維持呼吸的大白鼠為研究模式，測量吸入硫氫化鈉霧氣對肺迷走C纖維神經放電活性的影響。結果發現，此類神經對於化學性及物理性刺激的放電反應，皆在吸入硫氫化鈉後增強。再者，吸入半胱胺酸(一種硫化氫合成酶基質)也能引發此增強作用。硫氫化鈉對於此類神經的敏感化作用，在預先處理HC-030031後，被完全阻斷。另外，在肺迷走C纖維感覺神經的初代細胞培養模式下，單獨硫氫化鈉的給予，並不會影響神經細胞的胞內基礎鈣離子濃度，卻可增強辣椒素引發胞內鈣離子濃度的增加(Ca2+ transients) 。此增強作用，也可被HC-030031的前處理阻斷。綜合研究一的結果，我們推測硫化氫可作用於肺迷走C纖維神經上的TRPA1受器，造成此類神經的過度敏感，並進而增強呼吸暫停反應。
研究二：探討吸入卵白蛋白導致的呼吸道慢性發炎，如何增強呼吸道溫度提高引發的呼吸道收縮反應(一種經由肺迷走C纖維神經引發的軸突反射)。利用長期吸入卵白蛋白霧氣的Brown-Norway大鼠為呼吸道敏感化的研究模式，吸入兩分鐘的潮濕溫熱空氣，可使動物呼吸道溫度升高至約40.6°C，同時導致呼吸道阻力立即且持續(> 10分鐘)的增加。此呼吸道阻力增加的反應，在60-90分鐘後可以再現。然而，對照組動物(以生理食鹽水取代卵白蛋白)吸入潮濕溫熱空氣導致相同的呼吸道溫度升高，卻無法增加呼吸道阻力。這種在敏感化動物才能引發的呼吸道收縮，並非由吸入水氣所導致，因為吸入等量的潮濕室溫空氣，並無法引發呼吸道收縮。另外，潮濕溫熱空氣在敏感化動物引發的呼吸道收縮，不能被atropine (一種毒蕈鹼受器拮抗劑)的前處理所影響，卻會被neurokinin (NK)-1及NK-2兩種受器拮抗劑的合併前處理或formoterol (一種??2受器作用劑)的前處理完全抑制。綜合研究二的結果，在生理範圍的呼吸道溫度增加，可引發敏感化動物的呼吸道收縮，但對照組動物卻無此反應。我們推測此呼吸道過度敏感，可能來自於呼吸道慢性發炎增強肺迷走C纖維神經引發的軸突反射所致。
綜合兩篇研究的結果我們推測，肺迷走C纖維神經可藉由中樞神經型及局部軸突此兩種反射，參與呼吸道發炎引發的呼吸道過度敏感。此論文的結果，可增進肺迷走C纖維神經於臨床生理病理應用上的了解。並進而期盼，能對肺發炎疾病時呼吸道過度敏感的治療，提供有效的方針。

關鍵字

肺發炎 ； 肺C纖維 ； 呼吸道過度敏感

並列摘要

Airway hypersensitivity, characterized by exaggerated sensory and reflex responses to the same irritants, is a common pathophysiological feature in patients with airway inflammatory diseases such as asthma. Increasing evidence suggests that pulmonary vagal C-fibers are involved in the manifestation of various symptoms of airway hypersensitivity in these patients. However, the role of pulmonary vagal C-fibers in the inflammation-induced airway hypersensitivity is still unclear. Activation of the pulmonary vagal C-fibers is known to elicit various responses, such as apnea, cough, bronchoconstriction and airway hypersecretion, which are mediated through two types of neural pathways: centrally-mediated reflexes and local axonal reflexes involving the release of tachykinins from the nerve endings. Two studies were carried out to determine the mechanisms underlying the enhancement of C-fiber-mediated centrally-mediated reflexes and local axonal reflexes during lung inflammation.
Study 1 was carried out to determine whether airway exposure to H2S (a novel inflammatory mediator) leads to the enhancement of apnea which is a centrally-mediated reflex induced by C-fiber activation. In anesthetized, spontaneously breathing Sprague-Dawley rats, the inhalation of aerosolized sodium hydrosulfide (NaHS, a donor of H2S) caused no significant changes in the baseline breathing pattern. However, the apneic responses, presumably mediated through pulmonary vagal C-fibers, and triggered by right atrial injection of capsaicin were potentiated after inhalation of NaHS. This potentiating effect was prevented by pretreatment of HC-030031, an antagonist of TRPA1 receptors. After perineural capsaicin treatment of both cervical vagi to block the conduction of C-fibers, the enhancing apnea was also abolished, suggesting the pulmonary vagal C-fibers are important. To determine the effect of H2S on the pulmonary vagal C-fibers, the anesthetized and artificially ventilated rats were used. The afferent responses to the right atrial injection of capsaicin or phenylbiguanide and to lung inflation were all markedly potentiated after NaHS inhalation. Additionally, the potentiating effect on the afferent responses was found in rats inhaling L-cysteine (a substrate of H2S synthase). The potentiating effect of NaHS on the sensitivity of pulmonary vagal C-fiber afferents was completely blocked by pretreatment of HC-030031. In cultured pulmonary vagal sensory neurons, the perfusion of NaHS alone did not influence the intracellular Ca2+ concentration but markedly potentiated the Ca2+ transients evoked by capsaicin. The NaHS-caused effect in these sensory neurons was totally abolished by HC-030031 pretreatment. Taken together, these results suggest that H2S induces an enhancement of apneic reflexes in rats. The enhancement is mediated through a H2S-induced a nonspecific sensitizing effect on pulmonary C-fibers to both chemical and mechanical stimulation, which appears mediated through an action on the TRPA1 receptors expressed on the nerve endings of pulmonary vagal C-fibers.
Study 2 was carried out to determine the enhancing effect of allergic inflammation on the airway response to increasing airway temperature. Airway Inflammation was induced by airway exposure to ovalbumin (Ova) and enhancing bronchoconstriction was measured as an index of airway hypersensitivity. In Brown-Norway rats actively sensitized by chronic inhalation of Ova aerosol, hyperventilation with humidified warm air (HWA) for 2 min induced an increase in tracheal temperature to a peak of 40.6 ± 0.3°C and an immediate and sustained (> 10 min) increase in airway resistance (RL). The responses in RL were reproducible when the same HWA challenge was repeated 60-90 min later. In sharp contrast, the HWA challenge produced the same increase in tracheal temperature, but did not generate any increase in RL in matching control rats. In Ova-sensitized rats, the HWA-induced bronchoconstriction was not generated by the humidity delivered by the HWA challenge alone because the same water content delivered by saline aerosol at room temperature had no effect. The HWA-evoked increase in RL in Ova-sensitized rats was not blocked by atropine (a muscarinic receptor antagonist), but was completely prevented by a pretreatment with either a combination of neurokinin (NK)-1 and NK-2 antagonists, or with formoterol, a ??2-agonist, before the HWA challenge. We concluded that an increase in airway temperature within the normal physiological range triggered bronchoconstriction in Ova-sensitized rats, but not in control rats. Chronic airway inflammation in sensitized animals is likely a major contributing factor in causing this response.
In conclusion, pulmonary vagal C-fibers play a vital role in inflammation-induced airway hypersensitivity, which is mediated through centrally-mediated reflexes and local axonal reflexes. The outcomes of this study may provide a better understanding of the clinically significant physiology of pulmonary vagal C-fibers. Hopefully, it may potentially lead to novel strategies for improving the airway hypersensitivity during lung inflammation.

並列關鍵字

lung inflammation ； pulmonary vagal C-fibers ； airway hypersensitivity

參考文獻

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