Hypoxia causes contraction in pulmonary artery, whereas it causes relaxation in systemic artery. The purpose of this study is to test whether pulmonary artery would respond to metabolic inhibition and acidosis differently from ear artery. Rabbit pulmonary artery and ear artery were precontracted with phenylephrine or KCI, and then exposed to metabolic blockers (dlnttrophenof Hrlvl'), Na-cyanide (NaCN)) and acidosis. Contractile forces of ear artery induced by 30mM KCI and 1O-6M phenylephrine were 2-3times(n =7) and 5-9 times (n = 7) larger than that of the pulmonary artery, respectively, DNP and NaCN produced a dose-dependent relaxation in the pulmonary and ear artery, and the relaxation was more profound in the ear artery than in pulmonary artery. This effect was independent of the presence of the endothelium. Extracellular acidosis reduced the tone of the KCI-induced contraction, more in the ear artery than in pulmonary artery. These results indicate that pulmonary artery is more resistant to both of the inhibition of metabolism and acidosis than ear artery.