The measurement of inactive renin in human plasma: a consideration of methods

Does angiotensin regulate systemic conversion of prorenin to renin?

Within 12 hours of binephrectomy in rats, plasma prorenin rises about 250% above the pre-operative baseline and remains above-normal for at least 48 hours, indicating an extrarenal source of prorenin. Concurrently, active renin disappears, implying the loss of a renal "convertase" mechanism for prorenin activation. Such "convertase" activity was detected in incubates of renal cortical slices. To test the effect of angiotensin (Ang) on prorenin/"convertase" regulation, we infused Ang I (100 ng/kg/min) intraperitoneally for 24 hours and obtained evidence of "convertase" inhibition, as happened also following Ang II (2uM) addition to incubated cortical slices. Thus, the release and/or activity of "convertase" appears to be regulated by Ang in-vivo and in-vitro, suggesting that Ang controls not only direct renal renin release but also the secretion and/or activity of a renal "convertase" capable of producing additional renin from circulating prorenin pools.

A highly sensitive and reproducible immunoradiometric assay for total human renin using monoclonal antibodies, iodogen labelling and polystyrene star tubes

A two-site immunoradiometric assay for total renin concentration in human plasma is described. A new type of polystyrene tubes with a special bottom geometry, so-called Star Tubes were used. The lower limit of detection was 2 microIU per ml and the working range from 2 to 2000 microIU per ml. The variation for duplicate determinations on standards and plasma samples was 2.7% and the day to day variation was 4.8%. No significant interferences or cross reactivities were identified. EDTA-plasma was analyzed after dilution with a phosphate buffer. Plasma samples from different patient categories were analyzed. The results were compared with those obtained by our substrate enrichment method after acid activation of the samples had taken place. A linear correlation (r = 0.990) between the results obtained with the two methods was found.