Species dependent relaxation of intrapulmonary arteries (IPA) of rabbits, dogs and humans by prostacyclin

Abstract Helically cut strips of successive IPA segments of rabbits, dogs and human patients were set up for isometric recording in vitro . High tone was produced by norepinephrine (NE, 3 μM). This tone was markedly reduced by prostacyclin (PGI2) in the secondary, tertiary and quaternary branches of human and canine pulmonary trunk. The IC50 values for PGI2 ranged from 22 to 503 nM, the human vessels being more sensitive to prostacyclin than canine IPA. Under these conditions, the primary and secondary branches of the rabbit pulmonary trunk were not relaxed by PGI2. The contractile potency of NE was determined in each pulmonary vessel studied. The secondary segments of rabbit IPA were about ten times as sensitive to NE (EC50 for NE: 38±7 nM) as compared to the secondary IPA from dogs and humans (EC50 values: 370±84 and 440±50, respectively). When high tone was induced by equieffective contractile concentrations of NE (3 μM for canine and human IPA and 0.3 μM for rabbit vessels), PGI2 was still less effective (P