Relative contributions of direct and indirect mechanisms mediating endothelin‐induced contraction of guinea‐pig trachea

Abstract

1 The present study was undertaken to determine the mechanism of action of endothelin-l (ET-l)-induced contraction of the guinea-pig isolated trachea.2 ET-1 (1 nM-0.3 piM) produces a concentration-dependent contraction of guinea-pig trachea with an EC50 of approximately 25 nM. The combination of the peptidoleukotriene receptor antagonist, SK&F 104353 (10 JM) and the HI-histamine receptor antagonist, mepyramine (10 pM), which abolishes antigeninduced contraction in guinea-pig trachea, was without effect on ET-1 concentration-response curves.Furthermore, the platelet-activating factor (PAF) receptor antagonist, WEB 2086, (1 or 1O pM) did not inhibit ET-induced contraction. 3 ET-l (0.3 jiM) did not stimulate histamine or immunoreactive peptidoleukotriene release from guinea-pig isolated trachea. 4 The release of various prostanoids from guinea-pig trachea was increased significantly by ET-1 (0.3 jiM); the profile of release was prostaglandin D2 (PGD2) = PGE2 = 6-keto PGFi,, (PGI2 metabolite)> thromboxane B2 = PGFk >> 9a, 111, PGF2 (PGD2 metabolite). ET-1-induced release of prostaglandins, which was about 30% of that elicited by antigen in sensitized tissues, was not affected by epithelium removal and was observed in tissues from which the smooth muscle had been removed. Previous studies in our laboratory indicated that indomethacin potentiated contraction produced by high concentrations of ET-1, whereas a thromboxane receptor antagonist was without appreciable effect on ET-l concentration-response curves.5 Pretreatment of tissues for 1 h with capsaicin (1O jiM), which depletes different sensory neurones, produced a small, but significant, inhibitory effect on ET-1 concentration-response curves in the presence but not the absence of the epithelium. The combination of the NK, tachykinin receptor antagonist, CP-96,345 (0.1 pM), and the NK2 tachykinin receptor antagonist, SR 48968 (0.1 jiM), was without effect on ET-l concentration-response curves but substantially antagonized capsaicin-induced contraction. 6 The present data suggest that in guinea-pig isolated trachea, ET-1 produces contraction predominantly via a direct mechanism: there is no significant contribution of the release of histamine, leukotrienes, PAF, or tachykinins (acting on NK, or NK2 receptors). Although ET-1 evokes the release of an array of prostanoids from the trachea they do not appear to have a major influence on the contractile response.

Endothelins‐induce cyclicAMP formation in the guinea‐pig trachea through an ETA receptor‐ and cyclooxygenase‐dependent mechanism

“…Subsequently, the ability of ET-1 to contract non vascular smooth muscles was evident in intact animals and in isolated tissues (Takua, 1993). Airway smooth muscles (AWSM) and their epithelium were shown to synthesize, release and bind ET isopeptides, suggesting an autocrine and/or paracrine regulatory role for ETs in the airways (Hay et al, 1993;Ninomiya et al, 1995). In eliciting their biological responses in AWSM, ETs may activate a variety of signal cascades that include phospholipase C (PLC), PLD, PLA2, protein kinase C, tyrosine kinase and ion channels (reviewed by Rubanyi & Polokof, 1994).…”

“…The role of ETA receptor in this muscle is poorly understood. A controversy revolved around whether this receptor is functionally linked to muscle contraction (Hay et al, 1993) or is associated with attenuation of the contractile response triggered by the ETB receptor (Battistini et al, 1994).…”

“…Several studies revealed the synthesis and release of ET-1 from airway epithelium (Black et al, 1989;Hay et al, 1993;Ninomiya et al, 1995). Moreover, the presence of specific ET binding sites in airway muscles has been documented (Turner et al, 1989;Rozengurt et al, 1990;Hay et al, 1993).…”

“…Moreover, the presence of specific ET binding sites in airway muscles has been documented (Turner et al, 1989;Rozengurt et al, 1990;Hay et al, 1993). ET-1, on a molar basis, is a less potent constrictor in the airways than in vascular tissues.…”

“…ET-1, on a molar basis, is a less potent constrictor in the airways than in vascular tissues. Nevertheless, it is the most powerful airway constrictor ever isolated (Battistini et al, 1992;McKay et al, 1992;Hay et al, 1993). However, relaxant effects to ET-1 have been shown in pre-contracted rabbit trachea (Grunstein et al, 1991) and in guinea-pig trachea following anaphylactic reacAuthor for correspondence.…”