The interactions between prostacyclin (PGI2) and adrenergic, opiate, purinergic receptor agonists and antagonists were studied in isolated segments of guinea-pig ileum by recording the changes in isometric tension. The contractile response of these preparations to PGI2 was rapid and qualitatively similar to the effect of acetylcholine. Noradrenaline (30-300 nM) reduced the effect of PGI2 (20 nM) in a concentration-dependent manner. The inhibitory action of noradrenaline on PGI2-induced contractions was prevented by the alpha-blocker phentolamine and unaffected by the beta-blocker D(--)INPEA. Morphine (10,50 nM) antagonized the response of the ileum to PGI2 and naloxone prevented this inhibition. Also N6-phenylisopropyladenosine (PIA) (10,50 nM) inhibited the effect of PGI2, which was restored when theophylline was added before PIA. The present results indicate that presynaptic alpha-adrenergic, opiate and purinergic receptor stimulation operates a negative control on the effect of PGI2 in guinea-pig ileum.
Animals Epoprostenol