Action of three ectopeptidases on corticotropin-releasing factor: metabolism and functional aspects

Using purified enzyme preparations, we investigated the actions of angiotensin-converting enzyme, aminopeptidase N, and endopeptidase 24.11 on corticotropin-releasing factor (CRF). The effects of inhibition of these enzymes on CRF action in rat anterior pituitary cultures were also determined. Finally, specific inhibitors were used to evaluate ectopeptidase action on the regional brain metabolism of CRF. K(m) values for CRF were 165, 90, and 42 microM for angiotensin-converting enzyme, aminopeptidase N, and endopeptidase 24.11, respectively. A CRF metabolite profile for each enzyme was determined. In pituitary cultures, inhibition of endopeptidase 24.11 and aminopeptidase N potentiated CRF-stimulated release of adrenocorticotropic hormone (ACTH). In rat pituitary and hypothalamus membrane preparations, specific inhibitor experiments indicated that CRF hydrolysis involved members of the neutral endopeptidase and aminopeptidase enzyme families. In cortex membranes, similar peptidase inhibition was without effect. These data support the hypothesis that ectopeptidases play a major role in CRF metabolism and biological function.