title: Species variation in pulmonary endothelial aminopeptidase P activity.
abstract: Pulmonary endothelial aminopeptidase P (AmP) may be an important contributor to the inactivation of circulating bradykinin in certain species. To examine this possibility, we measured AMP activity in vivo and in vitro using Arg-Pro-Pro-[3H]benzylamide (3H-APPB) as substrate under conditions of first order enzyme kinetics. Utilizing multiple indicator dilution techniques, metabolism of 3H-APPB to Arg and Pro-Pro-[3H]benzylamide by AmP was not detectable during a single transpulmonary passage in anesthetized rabbits (n = 4), cats (n = 3) and pigs (n = 4). However, percent metabolism of 3H-APPB ranged from 54 to 63% in anesthetized rats (n = 6). In all experiments, the substrate remained within the vascular space and was thus accessible to endothelial and blood AmP only. At the same time, single-pass transpulmonary percent metabolism of [14C]benzoyl-Ala-Gly-Pro by endothelial-bound angiotensin converting enzyme was remarkably similar among rabbits, cats, rats and pigs (60-65%). In culture, Vmax/Km of AmP was 3 to 10 x 10(-4) min-1 for human basal arterial and rabbit and bovine pulmonary arterial endothelial cell monolayers (2 x 10(5) cells). AmP activity in the supernatant of lung and kidney tissue (homogenized in saline containing 1-o-n-octyl-beta-glucopyranoside) from rabbit, cat, pig and rat expressed as Vmax/Km(min-1) per (g wet tissue/ml) was 0.74, 2.25, 3.91 and 185.8 (lung), and 1.0, 3.7, 8.4 and 438.3 (kidney), respectively. Similarly, Vmax/Km values of AmP in plasmas of cat, dog, rabbit, pig, calf (serum), human and rat were 0, 0.016, 0.025, 0.068, 0.191, 0.237 and 3.53 min-1. These results suggest that 1) there are large interspecies variations in AmP activities of plasma, lung and kidney; 2) of the species studied, the rat contains the largest activities of AmP; and 3) AmP appears to be located on the luminal surface of the rat pulmonary endothelium.
authors.affiliation: Department of Pharmacology and Toxicology, Medical College of Georgia, Augusta.
authors.forename: X
authors.initials: X
authors.lastname: Chen
authors.forename: S E
authors.initials: SE
authors.lastname: Orfanos
authors.forename: J W
authors.initials: JW
authors.lastname: Ryan
authors.forename: A Y
authors.initials: AY
authors.lastname: Chung
authors.forename: D C
authors.initials: DC
authors.lastname: Hess
authors.forename: J D
authors.initials: JD
authors.lastname: Catravas
mesh_terms: D000626:Aminopeptidases / Q000097:blood / Q000378:metabolism*; D000818:Animals; D002415:Cats; D002417:Cattle; D002478:Cells, Cultured; D004730:Endothelium, Vascular / Q000166:cytology / Q000201:enzymology*; D005260:Female; D014644:Genetic Variation / Q000502:physiology*; D006801:Humans; D007668:Kidney / Q000201:enzymology; D007700:Kinetics; D008168:Lung / Q000098:blood supply / Q000201:enzymology*; D008297:Male; D011651:Pulmonary Artery / Q000502:physiology; D011817:Rabbits; D051381:Rats; D011919:Rats, Inbred Strains; D013045:Species Specificity; D013552:Swine; D013556:Swine, Miniature
chemical_list: D000626:Aminopeptidases; C022750:X-Pro aminopeptidase