Conversion of angiotensin I in isolated perfused guinea-pig and rat lung

Increasing concentrations of angiotensin I and different perfusion rates were used to study the conversion of angiotensin I in guinea-pig and rat lungs. Even the highest concentration used (32.0 muM), which is a thousand times higher than that which occurs in vivo, was unable to saturate the converting system indicating the enormous capacity of this system. SQ 20881 proved to be a reversible inhibitor of the converting system. Its effect on the angiotensin I conversion was greater in guinea-pig lungs than in rat lungs (ID50 was 40.0 nM in guinea-pig lung and above 360.0 nM in rat lungs at a substrate concentration of 38.6 nM).