LOCALIZATION AND QUANTITATION OF ACTIVE RENIN IN MONKEY KIDNEY BY RADIOINHIBITOR BINDING AND IN-VITRO AUTORADIOGRAPHY

We developed an in vitro autoradiographic method to localize and quant ify active renin in primate tissues. Active renin in monkey kidney sec tions was labeled with the primate specific renin inhibitor, H-3-CGP29 287, and quantitated with autoradiography and computerized densitometr y. Microscopic emulsion autoradiography was carried out to clarify the detailed localization of the binding. Nonspecific binding to aspartyl proteases other than renin was blocked using 1 mu mol/L of N-acetyl-p epstatin. To assess the usefulness of this procedure, binding of H-3-C GP29287 was examined both by film and emulsion autoradiography in the kidneys of monkeys (Macaca fuscata) that were given chronically either an angiotensin converting enzyme inhibitor (trandolapril), an angiote nsin II receptor antagonist (E4177), or vehicle. H-3-CGP29287 was foun d to bind very selectively to the juxtaglomerular apparatus (JGA) unde r control conditions. In monkeys treated with trandolapril or E4177, H -3-CGP29287 binding was increased in proportion to the increase in ren al renin concentration determined enzymatically; in these kidneys, emu lsion autoradiography revealed radioinhibitor binding extending far fr om the JGA. The potency of a series of unlabeled renin inhibitor in co mpeting for H-3-CGP29287 binding in the autoradiographic system closel y paralleled their potencies, as determined in inhibiting renin by an enzymatic assay. This technique permits specific labeling of the catal ytic site of renin in the monkey kidney sections.