Iloprost (ZK 36374) modulates the responses to beta-adrenoceptor agonists in guinea-pig airways and pulmonary vasculature

Abstract

The effect of iloprost on airway smooth muscles and its influence on the actions of beta-agonists and histamine were studied in the isolated perfused lung and isolated tracheal strips from guinea-pigs. Bolus injection of iloprost into the pulmonary artery elicited a concentration-dependent decrease in pulmonary perfusion pressure and an increase in airway resistance. These effects are not mediated through cholinergic, serotoninergic and histaminergic receptors. A rapid tachyphylaxis affected the effect of iloprost in airway resistance but not in pulmonary perfusion pressure. Iloprost did not induce a response in the isolated tracheal strips and did not alter the effect of histamine in both tracheal strips and airway resistance. This compound, however, caused an inhibition in the airway resistance-reducing effect of adrenaline and isoprenaline in the isolated perfused lung and a potentiation in the perfusion pressure-increasing effect of adrenaline. Iloprost also inhibited the relaxing effect of adrenaline and isoprenaline in the isolated tracheal strips precontracted with histamine and potentiated the inhibitory effect of propranolol against adrenaline and isoprenaline. From these results it was concluded that: Iloprost, a stable analogue of prostacyclin, modulates the beta-adrenoceptor blocking effect of propranolol in both airway smooth muscles and pulmonary vasculature.