The isolated lung model is a very useful model in investigation of hypoxic pulmonary vasoconstriction (HPV), and angiotensin II is extensively used in this model. But the exact role of angiotensin II in HPV is not clear in the isolated rabbit lung. Thus we were concerned about the role of angiotensin II in the blood-perfused rabbit lung.

New Zealand white rabbits (n = 28) lungs were isolated and perfused with a constant pulmonary perfusate flow; acid-base status and temperature were maintained at constant levels. Deoxyglucose (DOG group, n = 7), angiotension II and deoxyglucose (AG-DOG group, n = 7), calcium (CA group, n = 7), angiotensin II and calcium (AG-CA group, n = 7) were administered, and then hypoxic responses were measured. Three ratios were calculated and compared (P alpha: ratio of hypoxic response to pulmonary arterial pressure at normoxia, P beta: ratio of hypoxic response to baseline hypoxic response, P gamma: ratio of pulmonary arterial pressure at hypoxia to pulmonary arterial pressure at baseline).

Angiotensin II increased the pulmonary arterial pressure by 14%, and increased HPV. Baseline pulmonary pressure was increased in the AG-DOG group and in the AG-CA group (P<0.05). P gamma significantly increased in the AG-DOG and AG-CA groups (P<0.05). The first HPV increased but the second HPV decreased in the AG-DOG group (P alpha: P<0.05) and in the AG-CA group. P beta showed no difference between groups.

Angiotensin II resulted in an increase of pulmonary arterial pressure in the isolated rabbit lung. One may misinterpret this as an potentiation of HPV, but HPV was not changed by angiotensin II. Therefore we deny the necessity for angiotensin II in the isolated rabbit lung model.