effects of dopamine and dobutamine on hyperoxic and hypoxic pulmonary vascular tone in dogs the pulmonary vascular effects of dopamine and of dobutamine have been reported variably in the literature we investigated the effects of dopamine and of dobutamine at doses of 10 and 20 microgramskgmin on the relationships of overall mean pulmonary arterial pressure ppa to cardiac index cl in 14 dogs ventilated alternatively in hyperoxic fio2 04 and in hypoxic fio2 01 conditions fivepoint ppacl plots were constructed by opening an arteriovenous femoral fistula or by stepwise inflations of a balloon in the inferior vena cava these ppacl plots were rectilinear in all experimental conditions hypoxia was associated with an increase in ppa over the entire range of cl studied 2 to 5 lminm2 a deterioration in arterial oxygenation and an increase in o2 consumption constantly occurred after dopamine as well as after dobutamine administration at 10 microgramskgmin n 6 dogs neither drug affected ppa over the entire range of cl at both 04 and 01 fio2 at 20 microgramskgmin n 8 dogs dopamine and dobutamine increased ppa at the lowest cl 2 to 4 and 2 to 3 lminm2 respectively at 04 fio2 and attenuated hypoxiainduced increases in ppa over the entire range of cl two repetitions of alternated 04 and 01 fio2 exposures had no effect on ppacl plots in 6 additional dogs given no drug we concluded that at dosages as great as 20 microgramskgmin as generally given in clinical practice dopamine and dobutamine exerted similar effects upon the pulmonary circulation of intact dogs either no change or an increase in hyperoxic pulmonary vascular tone and either no change or an attenuation of hypoxic pulmonary vasoconstriction