Renin assay

The activities of renin in plasma and serum are measured in the diagnosis of hypertension. The natural substrate for renin is angiotensin. Several synthetic peptides have been used in renin assays. Recently, Nakamura-lmajo et al. (1992) used N-(2-pyridyl)glycine (pg) as a fluorescent tag on a nonapeptide. 

Positron-emission tomography Renin assay plasma renal vein Tilt-table testing... 

Prostate sonogram Prostate-specific antigen PSA velocity Protein, urine Renal angiography Renal biopsy Renal scanning Renin assay plasma renal vein... 

Rabies-neutralizing antibody test Red blood cell count Red blood cell indices Renin assay plasma renal vein Reticulocyte count Rheumatoid factor Rubella antibody test Sexually transmitted diseases Sickle cell test... 

Renin assays can be useful in distinguishing between primary and secondary aldosteronism. It can be measured by its enzymic action on angiotensinogen, the product, angiotensin I, being measured by radioimmunoassay. 

Samples (1.0 ml each) of a pool of pregnancy plasma were shaken at 37 C in polythene test-tubes with 0.1 ml of a suspension of Enzite-trypsin, an insoluble trypsin coupled to agarose (Miles Laboratories Ltd.). At various intervals the Enzite-trypsin was removed by centrifugation, 0.5 ml of the supernatant plasma was removed, dialysed against pH 7.0 assay-buffer and assayed renin. Figure 3 shows that pretreatment with trypsin resulted in an increase in renin concentration. If pH 7.4 phosphate buffer was incubated with Enzite-trypsin, the trypsin-free supernate assayed, no renin activity was present. This indicates that the increase in renin concentration after treatment with trypsin was not due to an effect of residual trypsin on the renin assay system. The pH of plasma after 24 hr incubation with trypsin was 7.6. Loss of renin activity occurred in the plasma incubated at 37°C without trypsin. 

The great interest devoted to angiotensin was due to its supposed rdle in hypertension genesis. As the action of renin generates angiotensin, several workers have proposed methods of renin assay based on the determination of angiotensin... 

This same approach was used for assaying other protease activities such as chy-motrypsin and renin [49], Chymotrypsin and renin cleave only at specific sites of... 

Figure 1. Amino acid sequences of renin inhibitors based on the amino acid sequence of angiotensinogen. Details of the synthesis and assay are given in references 11, 13, and 14.

GT Wang, CC Chung, TF Holzman, GA Krafft. A continuous fluorescence assay of renin activity. Anal Biochem 201 351-359, 1993. 

Despite tremendous progress in the field, drugs that cure Alzheimer s disease are still years away. Advances in /i-secretase assay technology, combined with the availability of structural information, will profit from previous lessons learned on renin and HIV-protease. /i-Secretase inhibitors are, therefore, likely candidates for... 

Interpretation Responses must be defined for the assay technique used. Patients with renin-dependent forms of hypertension (e.g., renovascular hypertension) show values that are approximately five times normal. Stimulated responses are also seen in patients with high-renin essential hypertension, pheochromocytoma, and Barttei s syndrome. Patients with hypertension firom mineralocorticoid excess (e.g., primary aldosteronism) usually have PRA below the concentration of assay sensitivity. Patients with hyporeninemic hypoaldosteronism usually have low concentrations of plasma renin and low aldosterone concentrations. Figure 51-17 shows typical responses. 

Most clinical laboratories measure PR A using an enzyme Idnetic assay m which angiotensin I is formed by the action of renin on its substrate, angiotensinogen. - Angiotensin... 

To obtain the maximum rate of renin activity, saturating amounts of the renin substrate, angiotensinogen, should be present in the reaction system. In most procedures, however, the only substrate provided is that present in the test plasma, and its concentration can be quite variable. According to some investigators, PRA is best estimated when the plasma specimen is incubated with an excess of exogenous renin substrate prepared from nephrectomized human subjects, oxen, or sheep. This type of assay is usually known as a plasma renin concentration assay rather than PRA assay. Unfortunately the measured renin depends on the source and concentration of the renin substrate. Synthetic peptides that resemble the M-terminal portion of angiotensinogen have also been used as renin substrates, but these substances can be hydrolyzed by nonspecific plasma proteases. 

A number of commercial kits are available for determining PRA " the basic elements of these procedures are summarized in the following sections. With continued improvements and availability of the immunometric assay methods for determining renin mass, renin activity assays will likely be replaced by the direct mass assays for the routine assessment of plasma renin. 

The incubated and nonincubated aliquots are then assayed for angiotensin I. Incubated plasma represents the endpoint of renin activity, whereas the 4 plasma represents renin activity at baseline. 

Plasma specimens must be buffered. Otherwise, the pH will increase during enzymatic incubation at 37 C, in which case the rate of angiotensin I generation wiU decrease owing to a shift in the kinetics and to the destruction of renin above pH 8. Thus assays use a buffer near the pH optimum of renin (5.7 to 6.3). 

Sealey J, Campbell G, Preibisz J. Hormone assays Renin, aldosterone, peripheral vein, and urinary assays. In Laragh J, Brenner B, eds. Hypertension pathophysiology, diagnosis, and management. New York Raven Press, 1990 1443-60,... 

Sealey J. Plasma renin activity and plasma prorenin assays. Clin Chem 1991 37 1811-9. 

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