Tissue distribution of 14C- and 35S-captopril in rats after intravenous and oral administration

35S-Captopril (50 mg/kg) administered i.v. to rats resulted in radioactivity being widely distributed into highly vascular tissues and into excretory organs. After oral administration of 14C-captopril (50 mg/kg), radioactivity in most tissues declined at a rate similar to that in blood. Concn. greater than those in blood were found only in kidney, liver and lung. The high concn. of 14C in kidney and liver were due to the excretory role of these organs. The high concn. of 14C in lung may be due to the high binding affinity of captopril to angiotensin-converting enzyme, present in large quantity in lung.