Acute pro‐inflammatory actions of endothelin‐1 in the guinea‐pig lung: involvement of ET A and ET B receptors

1 Although recent observations suggest that endothelin‐1 (ET‐1) may play a role in the pathogenesis of asthma, to date little is known about the effects of ET‐1 on parameters other than bronchoconstriction. The objectives of the present experiments were to study whether intravenously administered ET‐1 could exert pro‐inflammatory actions in the guinea‐pig lung and to assess the involvement of endothelin ET A and ET B receptors in these events by using the ET A receptor‐selective antagonist, FR 139317, the novel ET A /ET B receptor antagonist, bosentan and the ET B receptor‐selective agonist, IRL 1620. 2 Bolus i.v. injection of ET‐1 (0.1‐1 nmol kg −1 ) to anaesthetized guinea‐pigs evoked dose‐dependent increases in mean arterial blood pressure which lasted for 6‐12min. This was accompanied by a dose‐dependent haemoconcentration (8–15% plasma volume losses) and increases (up to 546%) in albumin extravasation in the trachea, upper and lower bronchi, but not in the pulmonary parenchyma. Qualitatively similar changes were observed following i.v. injection of the ET B receptor agonist, IRL 1620 (0.3 and 1 nmol kg −1 ), although IRL 1620 appeared to be about 3 times less potent than ET‐1. The ET A receptor‐selective antagonist, FR 139317 (2.5mg kg −1 ) inhibited the ET‐1 (1 nmol kg −1 )‐induced pressor response, haemoconcentration and albumin extravasation by 75, 77 and 60–70%, respectively, whereas it did not attenuate IRL 1620 (1 nmol kg −1 )‐induced changes. The ET A /ET B receptor antagonist, bosentan (10 mg kg −1 ) almost completely inhibited the pressor, haemoconcentration and permeability effects of both ET‐1 and IRL 1620. 3 ET‐1, but not IRL 1620 (0.1‐1 nmol kg −1 ), produced a dose‐dependent neutropenia with relative lymphocytosis and monocytosis, but did not induce influx of neutrophil granulocytes into pulmonary tissues or the bronchoalveolar space. ET‐1 (1 nmol kg −1 )‐induced neutropenia was prevented by pretreatment of the animals with FR 139317 (2.5 mg kg −1 ), bosentan (10 mg kg −1 ) or adrenaline (90 nmol kg −1 ), indicating that ET‐1 caused intravascular sequestration of neutrophil granulocytes. 4 ET‐1 or IRL 1620 (10 −1 ‐10 −6 m ) alone did not activate alveolar macrophages in vitro , whereas at a concentration of 10 −8 m , ET‐1, but not IRL 1620, markedly potentiated superoxide production in response to f‐Met‐Leu‐Phe (10 −9 ‐10 −7 m ) and platelet‐activating factor (PAF, 10 −9 ‐10 −7 m ), but not to phorbol 12‐myristate 13‐acetate (10 −9 m ). ET‐1 did not affect f‐Met‐Leu‐Phe‐ or PAF‐induced increases in intracellular free calcium concentration. This potentiating effect of ET‐1 was abolished by FR 139317 (1.5 × 10 −7 m ). 5 We conclude that, in addition to evoking airway contractions, ET‐1 exerts pro‐inflammatory actions via activation of the ET A and to a lesser extent the ET B receptors, and therefore, might contribute to the airway inflammation present in asthma. These findings also suggest the therapeutic potential of ET A /ET B receptor and perhaps ET A receptor‐selective antagonists in this disease.