Induction by endothelin‐1 of epithelium‐dependent relaxation of guinea‐pig trachea in vitro: role for nitric oxide

Abstract

The purpose of the present experiments was to study the underlying mechanisms responsible for the relaxant action of endothelin‐1 (ET‐1) in the guinea‐pig trachea in vitro. In tracheal strips precontracted (60–70% of the maximum) with carbachol, ET‐1 (1–100 nm) evoked slowly developing concentration‐dependent relaxations. Preincubation of the tissues with the thromboxane A2/prostaglandin H2 receptor antagonist, BM 13505 (5 μm) significantly potentiated the relaxant response to ET‐1. Removal of the epithelium changed the response of precontracted tracheal preparations to ET‐1 from a relaxation to a sustained contraction. ET‐1‐induced relaxations were abolished by methylene blue (10 μm) and were almost completely attenuated by oxyhaemoglobin (5 μm) and NG‐monomethyl‐l‐arginine (l‐NMMA, 100 μm), an inhibitor of nitric oxide synthesis, but were not altered by indomethacin (10 μm). In tracheal strips under passive tension, ET‐1 (1–100 nm) elicited dose‐dependent contractions. The sensitivity of tissues to ET‐1 was significantly enhanced by removal of the epithelium (apparent EC50 values were 28.1 ± 4.1 and 12.5 ± 0.8 nm in intact and rubbed trachea, respectively, n = 7, P < 0.01). Preincubation of intact tracheal strips with methylene blue, oxyhaemoglobin or l‐NMMA did not mimic the effect of epithelium removal on ET‐1‐induced contractions. There was a concentration‐dependent increase in thromboxane A2 but not in PGE2 and prostacyclin release from intact tracheal strips following stimulation with ET‐1 (5–100 nm). These results show that ET‐1 exerts a dual action on guinea‐pig isolated trachea: it evokes contractions at low resting tone, whereas it induces relaxations at higher resting tone. The relaxant action of ET‐1 may be mediated by nitric oxide released from epithelial cells and resultant activation of smooth muscle guanylate cyclase.

Nitric Oxide in Health and Disease of the Respiratory System

“…Bradykinin, endothelin-1, substance P, adenosine, and calcitonin-gene related peptide, applied to the inside of intact tracheal tubes, provoke concentration-dependent relaxations (9,93,(101)(102)(103)316). The relaxations are reversed into contractions (or contractions are markedly potentiated) by NOS inhibitors, indicating that the relaxant effect in the airways is mediated by the release of endogenous NO (9,93,(101)(102)(103)316).…”

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

“…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). However, in some preparations, the peptide induced vasodilatation as well as smooth muscle relaxation, a finding which suggested the coupling of ET-receptors to cyclicAMP and/or cyclicGMP formation (Oda et al, 1992;Eguchi et al, 1993;Filep et al, 1993;EL-Mowafy & AbdelLatif, 1994). …”

“…Additionally, ET-1 was shown to activate nitric oxide production, thereby producing a concentration-dependent relaxation of guinea-pig trachea (Filep et al, 1993).…”

The effects of calcitonin gene‐related peptide on tracheal smooth muscle of guinea‐pigs in vitro

“…One proposed EpDRF is prostaglandin E2 (PGE2) which is produced by T epithelial cells and has a potent relaxing effect on airway smooth muscle (Barnett et al, 1988). On the other hand, NO may be another EpDRF, since NO is also released from airway epithelium and relaxes airway smooth muscle (Dupuy et at., 1992;Filep et al, 1993). CGRP relaxes thoracic aorta and gastric microvasculatures by releasing NO (Gray & Marshall, 1992;Holzer et al, 1993).…”

“…Epithelium-derived relaxing factors (EpDRF) including prostanoids and NO, cause airway relaxation (Barnett et al, 1988;Filep et al, 1993). On the other hand, airway epithelium is capable of releasing endothelin-1 (ET-1), which is a potent bronchoconstrictor (Uchida et al, 1988;Ninomiya et al, 1992).…”