Kinetics of renin-antirenin reaction: micromethods for the assay of renin and antirenin

Inhibition of rat renin by antibody elicited against pure mouse renin and the effect on blood pressure

Antibodies raised against mouse submaxillary renin showed affinity for rat renal renin. The affinity was characterized by enzyme kinetics in vitro. The antibodies and the purified Fab fragments showed total inhibition of rat renin, with a Ki of 6.5 +/- 0.7 x 10(-8)mol/l for the Fab fragments. The effect of enzymatic inhibition on blood pressure in anaesthetized rats was compared with converting enzyme inhibition. The antibodies showed a significant effect on blood pressure, with a depressor effect corresponding to that of the converting enzyme inhibitor [SQ 20 881]. The reduction of mean arterial pressure was from 116 +/- 3 to 108 +/- 3 mmHg for the antibodies and to 107 +/- 4 mmHg for the converting enzyme inhibitor. The pressor response of infused rat renal renin was totally blocked by the antibodies while pressor responses of angiotensin II were unchanged.

Micromethod for the assay of renin of seven species

Renin was extracted and purified from human, dog, hog, rat, beef, rabbit and sheep kidneys. The renin "concentration" of these preparations was determined and expressed in international (Goldblatt) units by measuring the pressor effect produced by intravascular injection into normal dogs of a permanent colony. The renin "activity" was determined by bioassay, in the rat, of the angiotensin produced by incubation in vitro with renin substrate prepared from the serum of nephrectomized dogs. The rate of angiotensin formation was proportional to the concentration of renin, independent of the substrate concentration, and rather similar for renin of all seven species (mean rate = 55 x 10(4) ng angiotensin/unit renin/16 hrs). Due to this uniformity, either of the two international reference preparations of renin (human or hog) from the World Health Organization can serve as an internal standard in the assay of reninof each of the seven species, to express their concentration in terms of the international unit. Renin substrate from hog plasma was suitable for the assay of human, dog and hog renin (mean rate = 55 x 10(4)). However, it reacted much more slowly with the renin of rat, beef, rabbit and sheep (mean rate = 9 x 10(4)) and was, therefore, less suitable for their assay.