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To investigate the mechanism of tissue uptake of renin.Angiotensin peptide formation in tissues is dependent on kidney-derived renin, leading us to hypothesize that tissues possess a mechanism for uptake of renin from plasma.The binding of [125l]-labelled renin to membranes prepared from various rat tissues was examined. [125l]-labelled renins were cross-linked to membranes with disuccinimidyl suberate and analysed by sodium dodecyl sulphate-polyacrylamide gel electrophoresis followed by autoradiography.Mesenteric artery membranes bound both [125l]-labelled rat renin and [125l]-labelled mouse submandibular gland renin. Cross-linking experiments showed two bands, one of relative molecular mass approximately 105 000 and the other of approximately 75 000. After taking into account the molecular weight of renin, these bands represent renin-binding proteins of relative molecular mass approximately 70 000 and approximately 40 000, respectively. The highest level of these binding proteins was in the mesenteric artery; lower levels were found in the aorta, lung and renal medulla. Renin-binding proteins were also identified in membranes prepared from cultured rat aortic smooth muscle cells. No binding proteins were identified in the kidney cortex, heart, adrenal capsule, adrenal medulla, periaortic brown adipose tissue, uterus or pituitary. Binding of renin to mesenteric artery membranes was prevented by inhibitors of renin enzymatic activity (H-77 and SQ 30697); this effect of H-77 showed a dose-dependence parallel to the inhibition of renin activity by this compound, suggesting that the binding of H-77 to the active site of renin prevents its binding to the membranes.These studies provide evidence for a vascular renin-binding mechanism, which may play a role in the generation of angiotensin peptides in vasculature, and may thus be a determinant of blood pressure. Moreover, one of the actions of inhibitors of renin enzymatic activity in vivo may be to prevent the binding of renin to the vasculature.