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More on Renin

Dept. Internal Med. I, Univ. Hosp. Dykzigt, Dr Molewaterplein 40, 3015 GD Rotterdam, The Netherlands
^a Author for correspondence.

To the Editor:

In an editorial comment (1) on our paper (2), Sealey and Laragh erroneously conclude that the IRMA is a step backward from the traditional enzyme-kinetic plasma renin activity (PRA) assay, and that the new IRMA is not suitable for measuring renin because it comeasures 1–2% of prorenin.

They regard the traditional PRA assay as an accurate measure of the in vivo production of angiotensin (Ang) II, the physiologically relevant end product of the renin–angiotensin cascade. In fact, the PRA assay measures the concentration of Ang I that is generated in plasma in vitro after a long incubation period (up to 18 h) under artificial conditions. The PRA assay is an indirect assay of renin and is complicated by the fact that Ang I is usually converted to Ang II and degraded into smaller inactive peptides. Ang I-to-II conversion and Ang I degradation are prevented by lowering the pH of plasma and by adding peptidase inhibitors before the incubation step. Whether this is 100% successful, particularly with such long incubation times, has not been formally tested. These difficulties are not encountered in the direct assay of renin by IRMA.

The prorenin concentration in plasma is higher than the renin concentration, and comeasurement of even a small percentage of prorenin may therefore lead to a sizable overestimation of renin. The important question is: What is the true magnitude of this problem? Our study was designed to address precisely this question, and the answer is simple: The problem is not important enough to render the IRMA unsuitable for clinical use. In contrast to what is stated in the editorial comment, our study demonstrates that the the new assay can readily distinguish low-, normal-, and high-renin hypertension. There was good agreement with the enzyme-kinetic assay not only in the . . . [Full Text of this Article]

Footnotes

References

Jean E. Sealey, Daniel Catanzaro and John H. Laragh

Cardiovascular Center, New York Hosp.–Cornell Univ. Med. College, 525 E. 68th St., New York, NY 10021
^a Author for correspondence.

Acknowledgments

References

The following articles in journals at HighWire Press have cited this article:

				R. A. de Bruin, A. Bouhuizen, S. Diederich, F. H. Perschel, F. Boomsma, and J. Deinum Validation of a New Automated Renin Assay Clin. Chem., November 1, 2004; 50(11): 2111 - 2116. [Abstract] [Full Text] [PDF]

				J. Deinum, F. H.M. Derkx, and M. A.D.H. Schalekamp Improved Immunoradiometric Assay for Plasma Renin Clin. Chem., June 1, 1999; 45(6): 847 - 854. [Abstract] [Full Text] [PDF]