Subcellular localization of angiotensin II in kidney and adrenal

Objectives To investigate whether tissue angiotensin II generation occurs i ntra- or extracellularly, we studied the subcellular localization of angiot ensin 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 loca lization 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 homo genized tissue, were characterized using organelle-specific markers. Results I-125-angiotensin II and angiotensin Il were present in all organel les, with identical distribution profiles. In mitochondria-enriched fractio ns the relative specific activities [RSAs = (concentration per mg protein i n fraction)/(concentration per mg protein in homogenate)] of the two peptid es were similar to those in homogenate, whereas in cytosol-enriched fractio ns their RSAs were five-to 10-fold lower (P < 0.05 versus homogenate). In m icrosome- as well as in lysosome-enriched fractions the RSAs of I-125-angio tensin II and angiotensin II were two- to four-fold higher than in homogena te (P < 0.05), and their RSAs were also higher in renal nuclei-enriched fra ctions (P< 0.05). Eprosartan increased plasma angiotensin II to a larger de gree than tissue angiotensin II and greatly reduced tissue I-125-angiotensi n II. This led to similar decreases in the tissue/plasma concentration rati os 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 pre dominantly extracellularly, and is followed by rapid AT(1) receptor-mediate d endocytosis, thereby leading to high intracellular angiotensin II levels.