Subcellular localization of angiotensin II in kidney and adrenal

Objectives To investigate whether tissue angiotensin II generation occurs intra- or extracellularly, we studied the subcellular localization of angiotensin II in kidney and adrenal, two organs with high endogenous angiotensin II concentrations. Design and methods Tissues were obtained, following a 1 h infusion of I-125-angiotensin I or I-125-angiotensin II to simultaneously determine the localization of plasma-derived angiotensin II, from five control pigs and four pigs that had been pretreated with the AT(1) receptor antagonist eprosartan, Subcellular organelles, prepared by differential centrifugation from homogenized tissue, were characterized using organelle-specific markers. Results I-125-angiotensin II and angiotensin Il were present in all organelles, with identical distribution profiles. In mitochondria-enriched fractions the relative specific activities [RSAs = (concentration per mg protein in fraction)/(concentration per mg protein in homogenate)] of the two peptides were similar to those in homogenate, whereas in cytosol-enriched fractions their RSAs were five-to 10-fold lower (P < 0.05 versus homogenate). In microsome- as well as in lysosome-enriched fractions the RSAs of I-125-angiotensin II and angiotensin II were two- to four-fold higher than in homogenate (P < 0.05), and their RSAs were also higher in renal nuclei-enriched fractions (P< 0.05). Eprosartan increased plasma angiotensin II to a larger degree than tissue angiotensin II and greatly reduced tissue I-125-angiotensin II. This led to similar decreases in the tissue/plasma concentration ratios of I-125-angiotensin II and angiotensin II. The subcellular distribution of both angiotensin Il peptides was not affected by eprosartan, Conclusions Local angiotensin II synthesis in adrenal and kidney occurs predominantly extracellularly, and is followed by rapid AT(1) receptor-mediated endocytosis, thereby leading to high intracellular angiotensin II levels.