The preparation of rabbit renin-substrate for the assay of minute amounts of renin

Immunocytochemical localization of angiotensinogen in rat liver and kidney

The renin substrate, angiotensinogen, was localized by immunocytochemistry in liver and kidney of normal rats by the use of an antiserum directed against pure rat angiotensinogen. This substrate was also examined in rats after bilateral nephrectomy, which is known to increase plasma angiotensinogen, and in rats treated with colchicine, which inhibits serum protein secretion. In normal rat liver, light microscopy showed the presence of immunoreactive material in a very few cells. The number of stained hepatocytes rose in rats treated with colchicine or after bilateral nephrectomy. Immuno-staining increased further when rats were both nephrectomized and colchicine treated. In the kidney, angiotensinogen was specifically located as granular formations in nephrocytes of the proximal tubule but never in the granular cells of the juxtaglomerular apparatus. The localization of these granular formations under the brush border suggests that angiotensinogen is reabsorbed from the glomerular ultrafiltrate rather than synthesized in the kidney.

Purification and partial characterization of human angiotensinogen

Renin substrate was initially extracted from human plasma by (NH4)2SO4 followed by chromatography on Sephadex G-150, DEAE cellulose, calcium phosphate gel, isoelectric focusing and preparative polyacrylamide gel electrophoresis. On the basis of one mol of angiotensin per mol of substrate, the purity of the preparation is in excess of 95%. On analytical polyacrylamide gel electrophoresis in the presence of 1% sodium dodecyl sulfate or 8 M urea, the protein appears homogenous. In addition, the purified protein shows only one preciptin line against anti-normal human serum on either Ouchterlony immunodiffision or immunoelectrophoresis. The biological activity appears similar to "native" renin substrate since the Km is the same as that reported for the renin reaction in whole plasma. The molecular weight was determined as 110 000 by gel filtration and polyacrylamide gel electrophoresis; amino acid analysis of the human substrate differs from that reported for hog, especially in the Asp, Glu and Gly composition.

A rapid simple method for the assay of renin in rabbit plasma

1. EDTA (10mm), 2,3-dimercaptopropan-1-ol (10mm) and chlorhexidine gluconate (0.005%, w/v) cause complete inactivation of plasma enzymes that degrade angiotensin I, but have no effect on the reaction of renin with its substrate. The reagents were termed the selective inhibitors. 2. Thus it is possible to measure renin in plasma by its ability to catalyse the release of angiotensin I. 3. Sterile plasma, treated with the selective inhibitors, is incubated with renin substrate (500-1000ng. of angiotensin content/ml.) at pH6 at 42 degrees for 6hr. 4. Under these conditions the reaction obeys first-order kinetics. Renin activity is calculated in terms of the percentage release of the angiotensin content/hr. 5. As described, the assay is sufficiently sensitive to measure renin in the plasma of all normal rabbits. By extending the length of the incubation, much lower activities can be measured.

Properties of renin substrate in rabbit plasma with a note on its assay

1. Rabbit plasma enzymes that degrade angiotensin I are inhibited completely by the combination of 2,3-dimercaptopropan-1-ol (10mm), EDTA (10mm) and chlorhexidine gluconate (0.005%, w/v). These compounds do not modify the reaction of renin with renin substrate and are termed the selective inhibitors. 2. The renin substrate concentration of plasma can be measured as angiotensin I content by incubating plasma plus the selective inhibitors with renin for a time sufficient to allow complete utilization of renin substrate. 3. This reaction obeys first-order kinetics to substrate concentrations of at least 1000ng. of angiotensin I content/ml. In general, the renin substrate concentrations of normal rabbit plasmas are less than 1000ng. of angiotensin I content/ml. Thus the time required for the complete release of angiotensin I from normal plasma is inversely related to renin activity and is independent of renin substrate concentration. 4. A method for the assay of renin substrate, taking these reaction kinetics into account, is presented.

Cadmium, chromium, and cardiovascular disease

Observations made in the last 15 years by the author and others concerning the effect of trace metals, particularly cadmium and chromium, on animals and man are reviewed with special reference to hypertension and atherosclerosis. These trace metals come from the soil or sea. Among the topics covered are cadmium hypertension in rats, diabetes mellitus and chromium deficiency, deficiency sources, and possible losses of chromium, and the influence of drinking water on death rates from atherosclerosis. The conclusions are that one common form of hypertension is probably an example of accumulation of cadmium in the kidney and that deficiency of chromium may influence glucose and lipid metabolism and affect atherosclerosis. Other trace elements may contribute also.

Kinetic constants of the human renin and human angiotensinogen reaction

The rate of formation of angiotensin was investigated for the reaction of angiotensinase-free human renin, at various states of purity, with angiotensinogen, in pooled, angiotensinase-free human serum. The velocity constant of this reaction and the Michaelis constant of the renin-substrate complex were determined. The concentration of angiotensinogen and of endogenous renin in human serum was also determined and, on the basis of these results, a procedure was designed for the indirect assay of human renin. This was carried out under a wide range of experimental conditions, for periods of incubation ranging from 10 min to 18 hours, for various concentrations of substrate, and for renin concentrations varying from 0.000025 to 0.20 unit/ml. The absence of angiotensinase made possible the prolonged incubation (18 hours) of a minute quantity of renin with a large amount of the renin substrate. The resultant formation of large amounts of angiotensin permitted its accurate assay in the dog.

A sensitive method for assay of plasma renin activity

Renin activity is separated from rabbit plasma by globulin precipitation, dialysis, and DEAE cellulose column chromatography with a Tris chloride buffer system and acid elution, followed by ultrafiltration. The plasma renin extract contains no renin substrate and no angiotensinase activity can be detected after incubation with angiotensin for 200 hr. Incubation with a known concentration of rabbit renin substrate, similarly free of renin activity and angiotensinase, at pH 6.0 in 0.1 M phosphate buffer forms angiotensin-like activity at a constant rate for up to 200 hr. Recovery and reproducibility are satisfactory. Evidence is presented that the material in the plasma extract behaves similarly to renin and that the incubation product is indistinguishable from angiotensin.