Leukotkiene E 4 - induced airway hyperresponsivenlss of guinea pig tracheal smooth muscle to histamine and evidence for three separate sulfidopeptide ledkotriene receptors TAK

Bronchial hyperresponsiveness to contractile agonists and nonspecific irritants is a characteristic feature of bronchial asthma. The mechanisms causing this hyperirritability are unknown. The existence of separate receptors for leukotrienes C4 and D4 (LTCC4 and LTD4) has been, demonstrated previously by physiologic and radioligand binding studies. The rank order of potency of the sulfidopeptide leukotrienes for contracting tracheal spirals [leukotrwiene E4 (LTE4) > LID4 = LTC4J is different from that for contracting parenchymal strips (LTD4> LTE4> LTC4), thereby suggesting the existence of a separate receptor for LTE4. We now report that 'LTE4, the most stable of the leukotrienes comprising slow reacting substance of anaphylaxis, enhances the contractile response of guinea pig tracheal spirals but not of parenchymal strips, to histamine in a timeand dose-dependent fashion., The ability of LTE4 to increase histamine responsiveness occurred after removal of the free agonist and recovery of the tissues to baseline tensions and was not produced by lemkotrienes C4 and Lr4, which elicited the same magnitude of contraction of tracheal smooth muscle as LTE4. These findings suggest that LTE4-induced airway hyperirritability is not mediated by the contractile response per se and may be modiated through a receptor distinct from those for leukotrienes C4 and D4. A hallmark of bronchial asthma is the elicitation of bronchoconstriction by inhalation of contractile agonists and nonspecific irritants at concentrations that are not active on the airways of normal individuals (1-3). The mechanisms responsible for this characteristic of bronchial asthma, generally termed airway hyperresponsiveness, are unknown, although such a state can be created or enhanced by respiratory infections (4) or by inhalation of allergen in asthmatic subjects (5). The observation that partially purified slow reacting substance of anaphylaxis (SRS-A), released from guinea pig lung tissue by an immediate hypersensitivity reaction, could augment the contractile response of the isolated guinea pig ileum to histamine (6) suggested that the sulfidopeptide leukotrienes now identified as constituting SRS-A, (5S,6R)-5hydroxy-6-S-glutathionyl-7,9-trans-11,14-cis-icosatetraenoic acid (leukotriene C4, LTC4), (5S,6R)-5-hydroxy-6-S-cysteinylglycyl-7,9-trans-11,14-cis-icosatetraenoic acid (leukotriene D4, LTD4), and (5S,6R)-5-hydroxy-6-S-cysteinyl-7,9-trans11,14-cis-icosatetraenoic acid (leukotriene E4, LTE4) (7-10), might contribute to airway hyperresponsiveness. In normal subjects, inhaled LTC4 and LTD4 were 4000 and 6000 times more potent than histamine in eliciting a comparable impairment of pulmonary function, whereas in asthmatics, inhaled LTD4 was only 200 times more potent than histamine (11-13). The finding that a group of asthmatic subjects exhibited hyperresponsiveness to inhaled histamine but not to LTD4, as compared to normal individuals (13), suggested that LTD4 was acting at a site in the airways distinct from histamine and inight in addition be responsible for airway hyperresponsiveness to other substances. LTC4, LTD4, and LTE4 are potent contractile agonists for guinea pig tracheal spirals and parenchymal strips, with a molar ratio of the amounts eliciting equivalent contractions of 1:1:0.1'and 1:0.05:0.3, respectively (14). Thi's reversal of potency ratios for LTD4 and LTE4 with airway smooth muscle from the same species suggested separate receptors for each and prompted an examination of the capacity of these leukotrienes to elicit airway hyperresponsiveness of guinea pig pulmonary tissues to histamine. MATERIALS AND METHODS Tracheal spirals and parenchymal strips obtained from male guinea pigs (300to 400-g body weight) were prepared in vitro for recording of isometric contractions after a stable baseline tension had been established as described (15). The tissues were exposed to logarithmically increasing concentrations of histamine (0.1-100 gM) (Sigma) to construct a cumulative histamine concentration-effect relationship for each tissue preparation. The initial contraction elicited by 100 gxM histamine was assigned a value of 100, and all subsequent contractile responses to any agonist in that tissue were expressed as a percentage of this reference contraction. After conipletion of the initial histamine dose-response curve, the tissues were washed with oxygenated Tyrode's solution at 15-min intervals for 1 hr and were used either to establish a cumulative dose-response curve for a sulfidopeptide leukotriene or to assess responsiveness to histamine after exposure of the tissues to a defined dose of sulfidopeptide leukotriene. Synthetic leukotrienes, prepared by total chemical synthesis (16-18), were diluted in Tyrode's buffer and added to organ baths to establish cumulative dose-response curves within the range of 0.02-100 nM for LTE4 and LTD4 and 0.06-80 nM for LTC4. Alternatively, a defined concentration (0-80 nM) of synthetic leukotriene was added to each organ bath for 5-20 min, and the tissues were washed with 750 ml of buffer over 2 hr, during which time the tension of each fell to that recorded before leukotriene exposure; a second histamine concentration-effect relationship was then established on each tissue. The concentration of histamine that elicited a 50% maximum contraction (EC50) was interpolated from the second histamine dose-response curve for each tissue, and the geometric means of these EC50 values were computed (19). Abbreviations: SRS-A, slow reacting substance of anaphylaxis; LTC4, leukotriene C4; LTD4; leukotfiene D4; LTE4, leukotriene E4. The publication costs of this article were defrayed in part by page charge payment. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. §1734 solely to indicate this fact.