We examined angiotensinogen gene expression in rat kidney by in situ hybridization histochemistry. Using a rat cRNA probe to angiotensinogen, we demonstrated angiotensinogen mRNA to be localized predominantly in the proximal renal tubule, with considerably lesser amounts in distal tubular segments and glomerular tufts. Previous studies have localized renin immunoreactivity to the juxtaglomerular cells, glomerular tufts, and proximal tubules. Such findings provide further evidence for a local tissue renin angiotensin system within the kidney which may influence regional function. Based on our data, we hypothesize that a major site of angiotensin production is the proximal tubule. We postulate that angiotensin synthesized in and/or around the proximal tubule may directly modulate tubular transport of sodium, bicarbonate, and water. In addition to the proximal tubule, the specific localization of the renin angiotensin components elsewhere in the kidney would also support the other proposed regional functions of the intrarenal system, including modulation of tubuloglomerular balance. (J. Clin. Invest. 1990. 85:417-423.) renin -angiotensinogen * kidney-in situ hybridization -RNA

Recent data demonstrate the existence of a vascular renin angiotensin system. In this study we examine the localization of angiotensinogen mRNA in the blood vessel wall of two rat strains, the Wistar and Wistar Kyoto (WKY), as well as the regulation of vascular angiotensinogen mRNA expression by dietary sodium. Northern blot analysis and in situ hybridization histochemistry demonstrate that in both strains angiotensinogen mRNA is detected in the aortic medial smooth muscle layer as well as the periaortic fat. In WKY rats fed a 1.6% sodium diet, angiotensinogen mRNA concentration is 2.6-fold higher in the periaortic fat than in the smooth muscle, as analyzed by quantitative slot blot hybridization. Angiotensinogen mRNA expression in the medial smooth muscle layer is sodium regulated. After 5 d of a low (0.02%) sodium diet, smooth muscle angiotensinogen mRNA levels increase 3.2-fold (P < 0.005) as compared with the 1.6% sodium diet. In contrast, angiotensinogen mRNA level in the periaortic fat is not influenced by sodium diet. In summary, our data demonstrate regional (smooth muscle vs. periaortic fat) differential regulation of angiotensinogen mRNA levels in the blood vessel wall by sodium. This regional differential regulation by sodium may have important physiological implications. (J. Clin. Invest. 1991Invest. . 87:1300

We have identified and characterized an anti-human renin monoclonal antibody Rl-20-5 that is selective for human active renin. Rl-20-5 binds active renin with a dissociation constant (K d ) of 2.5x10"' M/l and inhibits renin enzymatic activity with an inhibitory constant (IC 50 ) of 1.4xlO~8 M/l. Rl-20-5 competes with a synthetic renin inhibitor for binding with renin, demonstrating further that it is binding to or close to the active site. This antibody does not bind prorenin in human plasma or recombinant prorenin expressed by L-929 fibroblasts transfected with human renin gene. Furthermore, trypsin activation of prorenin resulted in immunoreactivity of the activated prorenin toward the antibody. In addition, an immunoaffinity column of Rl-20-5 coupled to Sepharose retained active renin but had a low affinity for prorenin. A sensitive and rapid solid phase radioimmunoassay for active renin was developed using a "sandwich" technique employing Rl-20-5 and a second non-active site-directed monoclonal antibody to human renin. Renin levels in human plasma samples were determined by the standard enzymatic assay, and by the direct radioimmunoassay for active renin, before and after trypsin activation. Trypsin treatment of plasma resulted in parallel increases in both the plasma renin enzymatic activity and in the plasma active renin concentration as measured by the direct radioimmunoassay. Overall, plasma immunoreactive active renin concentration correlated significantly with plasma renin enzymatic activity (r=0.96,p<0.001). In summary, the monoclonal antibody Rl-20-5 is selective for human active renin and should be a very useful tool for studies of the active enzyme in humans.

Multiple lines of evidence (physiologic, immunohistochemical, and molecular biologic) support the presence of a complete intrarenal renin-angiotensin system (RAS). Localization of angiotensinogen messenger ribonucleic acid (mRNA) within the proximal tubule, together with demonstration of renin and converting enzyme mRNAs within the kidney, provide the most persuasive evidence for local, independent synthesis. Data from a combination of in situ hybridization studies, Northern analysis, and physiologic manipulations lead us to propose that a major site for action of a local RAS is the proximal tubule. There, locally generated angiotensins may regulate sodium reabsorption and urine pH. A variety of factors appear to regulate renal angiotensinogen. For instance sodium depletion increases the expression of renal angiotensinogen (as well as renin mRNA), as does high potassium intake and androgen administration. In pathologic states, such as experimental heart failure, and certain models of hypertension, such as the spontaneously hypertensive rat, expression of renal angiotensinogen mRNA levels is altered. It is proposed that changes in the intrarenal RAS may play a role in the maintenance of homeostasis and in the pathophysiology of various disease states.