Converting enzyme activity of free airway cells.

The pulmonary circulation was previously shown to inactivate and even activate a number of autacoids. Further studies showed that these enzymatic activities were localized in vascular endothelial cells. The present results shows that guinea pig free airway cells (FACs) convert angiotensin I to angiotensin II and inactivate bradykinin, whereas they do not inactivate serotonin, prostaglandin E2, histamine, and noradrenaline. In the presence of a converting enzyme inhibitor (SQ14225), the angiotensin I was not converted into angiotensin II, but bradykinin was still inactivated, although the speed of inactivation was decreased. Furthermore, when FACs were separated as adherent and nonadherent cells, the cleavage of angiotensin I by adherent cells was similar to that of the total cell suspension. The inactivation of bradykinin was more pronounced in incubation with nonadherent than with the adherent cells. Using selected enzyme inhibitors, we also showed that the conversion of angiotensin by FAC is the result of specific kinase II activity most likely located in macrophages, whereas the bradykinin inactivation is the result of the cooperation of many enzymes including kinase I and II produced by various cell types.