Am. J. Respir. Crit. Care Med., Volume 162, Number 2, August 2000, 528-533

Prostaglandin E₂ Enhances Chemical and Mechanical Sensitivities of Pulmonary C Fibers in the Rat

CHING-YIN HO, QIHAI GU, JU-LUN HONG, and LU-YUAN LEE

Department of Physiology, University of Kentucky, Lexington, Kentucky; and Department of Otolaryngology, Veterans General Hospital and National Yang-Ming University, Taipei, Taiwan, Republic of China

It has been recently reported that pulmonary reflex responses to injection or inhalation challenge of capsaicin are enhanced by exogenous Prostaglandin E₂ (PGE₂). The present study was carried out to determine whether PGE₂ enhances the stimulatory effects of chemical stimulants and lung inflation on vagal pulmonary C fibers, and if so, whether the excitabilities of other types of lung afferents are also augmented by PGE₂. In anesthetized, open-chest rats, administration of PGE₂ (1.5 µg/kg/min for 2 min) did not significantly change the baseline activity of vagal pulmonary C fibers, but it markedly enhanced the stimulatory effects of both low (0.25 µg/kg) and high doses (0.5 µg/kg) of capsaicin on these fibers. Similarly, potentiating effects of PGE₂ were found on the pulmonary C-fiber responses to injections of lactic acid and adenosine, although considerable variability existed in the degrees of potentiation between the different stimulants. Furthermore, PGE₂ infusion also significantly enhanced the C-fiber response to constant-pressure lung inflation (tracheal pressure [Pt] = 30 cm H₂O). In contrast, PGE₂ did not alter the responses of either slowly adapting pulmonary receptors or rapidly adapting pulmonary receptors to lung inflation. In summary, these results show that the sensitivity of pulmonary C-fiber afferents to both mechanical and chemical stimuli is enhanced by PGE₂, suggesting that endogenous release of this autocoid may play a part in the airway irritation and dyspneic sensation associated with airway inflammation.

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