Prostaglandin E₂ enhances chemical and mechanical sensitivities of pulmonary C fibers the rat

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.