Properties of angiotensin-converting enzyme in intact cerebral microvessels.
Angiotensin-converting enzyme (ACE) was studied in preparations of microvessels isolated from rabbit cerebral cortex. Activity was determined by measuring the degradation of hippuryl-histidyl-leucine (Hip-His-Leu) by the intact microvessels in a physiological salt solution at pH 7.4. ACE activity was dependent on both substrate and chloride ion concentration and was inhibited by captopril in a manner similar to that observed previously with tissue homogenates. Angiotensin I was rapidly degraded by the intact microvessels, even in the presence of 10(-6)M captopril. An advantage of the methodology employed was the ability to pretreat the microvessels and then assess the effect of pretreatment by transfer to a postincubation assay system. Pretreatment with a hyperosmolar urea solution did not change ACE activity or cause release of ACE from the microvessels, although lactic dehydrogenase and lysosomal enzymes were released. Pretreatment with captopril caused a lag in the subsequent degradation of Hip-His-Leu, presumably reflecting dissociation of inhibitor from the cell-associated enzyme. ACE activity was unaffected by hypoxic or anoxic incubation conditions. The ability to measure ACE activity of the microvessels in vitro provides a unique opportunity to study the properties of the enzyme in intact cerebrovascular endothelial cells.
D000818:Animals; D001681:Biological Assay; D001808:Blood Vessels / Q000187:drug effects / Q000201:enzymology*; D001921:Brain / Q000098:blood supply / Q000187:drug effects; D002216:Captopril / Q000494:pharmacology; D002540:Cerebral Cortex / Q000201:enzymology*; D003470:Culture Media; D005615:Freezing; D006626:Hippurates / Q000502:physiology; D000860:Hypoxia / Q000503:physiopathology; D007700:Kinetics; D008297:Male; D009842:Oligopeptides / Q000502:physiology; D009994:Osmolar Concentration; D007703:Peptidyl-Dipeptidase A / Q000378:metabolism / Q000502:physiology*; D011817:Rabbits
D003470:Culture Media; D006626:Hippurates; D009842:Oligopeptides; C010980:hippuryl-histidyl-leucine; D002216:Captopril; D007703:Peptidyl-Dipeptidase A