Aerosolized cysteinyl leukotrienes (CysLTs) elicit migration of eosinophils into guinea pig lungs and the airways of patients with asthma. The present studies were designed to analyze the concentration-response relationship, time course, and pharmacologic and histologic characteristics of leukotriene D4 (LTD4)-induced eosinophil influx into the airways of conscious guinea pigs. Animals were exposed to aerosols of 0.3 to 30 microg/ml LTD4 for 1 min, during which specific airway conductance (sGaw) was monitored. Bronchoalveolar lavages (BALs) of guinea pig airways were conducted at selected times from 4 h to 4 wk after LTD4 challenge. LTD4 produced maximal decreases in sGaw (70 to 90% reduction) at all concentrations tested and concentration-related increases in eosinophil levels in BALs, assessed 24 h after challenge. Increased numbers of eosinophils in the bronchial epithelium and subepithelium were confirmed histologically. Significant eosinophilia was maintained for up to 4 wk postchallenge. Pretreatment with the LTD4 receptor antagonist, pranlukast (ONO-1078, SB 205312) (20 mg/kg, intragastrically), significantly inhibited both the bronchoconstriction and the eosinophilia at 24 h, whereas the cyclooxygenase inhibitor, meclofenamic acid (5 mg/kg, intragastrically), had no effect on either parameter. Histologic observations were consistent with BAL results. Pretreatment with the rat anti-mouse antibody to interleukin-5 (IL-5), TRFK-5 (10-300 microg, intraperitoneally), produced dose-related inhibition of LTD4-induced eosinophilia, measured in 24 h or 3 wk BAL, but did not affect the acute bronchoconstriction. These results indicate that LTD4 elicits airway eosinophil influx in guinea pigs which persists as long as 4 wk after a single exposure, and provide the first evidence that IL-5 may have a role in LTD4-induced airways inflammation. This and other previously reported proinflammatory effects of LTD4 may contribute significantly to its overall influential role in the pathophysiology of asthma, and may underlie the therapeutic benefit of CysLT receptor antagonists, such as pranlukast, in this disorder.

Experiments were conducted to determine whether relaxation of the opossum isolated lower esophageal sphincter (LES), induced by electrical field stimulation (EFS) or various pharmacological agents, is associated with changes in cyclic nucleotide content. EFS relaxed the LES in a frequency-dependent manner with 0.7 Hz producing half-maximal relaxation. Control tissues and tissues stimulated at various frequencies were clamp-frozen and assayed for cyclic nucleotide content. EFS had no effect on adenosine 3',5'-cyclic monophosphate (cAMP) content but increased guanosine 3',5'-cyclic monophosphate (cGMP) content in a frequency-dependent manner. Tetrodotoxin eliminated both the relaxation and cGMP accumulation in response to EFS. Vasoactive intestinal polypeptide (VIP) relaxed the LES with an EC50 of 0.1 microM. In contrast to the results with EFS, VIP enhanced cAMP content but had no effect on cGMP content. Relaxation of the LES produced by sodium nitroprusside or atriopeptin II was accompanied by an increase in cGMP accumulation, whereas isoproterenol- and dopamine-induced relaxation was accompanied by an increase in cAMP content. The data indicate that, depending on the stimulus, increases in either cAMP or cGMP content can accompany LES relaxation. These results are consistent with the proposed role of cyclic nucleotides as second messengers mediating LES relaxation.

The relationship between glycogen phosphorylase activity (an index of cytosolic Ca2+ content), myosin light-chain phosphorylation, isotonic shortening velocity, and isometric tension was examined in canine trachealis. Responses were measured in tracheal strips contracted with various concentrations of methacholine or K+. Both agonists produced prolonged and concentration-dependent increases in isometric tension that reached 90% of the plateau level within 1 (methacholine) to 5 (K+) min and remained stable over 60 min. In contrast to the monotonic increase in isometric tension, shortening velocity reached a maximum almost immediately (12-48 s) after the addition of either methacholine or K+ and then declined over time to a steady-state level that was 25-40% of the peak. Phosphorylase activity also increased transiently, reaching a maximum 1-2 min after the addition of either agonist before declining to near-basal levels over the 60-min observation period. Unlike the increases in shortening velocity and phosphorylase activity, agonist-induced myosin phosphorylation was not markedly transient. Moreover, regardless of the contractile agonist used, no correlation was found between myosin phosphorylation and shortening velocity when these parameters were compared at corresponding time points. This suggests that myosin phosphorylation is not the sole determinant of shortening velocity in canine trachealis.

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