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The effect of different chemical reagents on renin has been investigated. After treatment of hog renin with acetic anhydride, 1-fluoro-2,4-dinitrobenzene, diazobenzene sulfonic acid and phenyl isocyanate, the enzymic activity assayed both biologically and chemically was depressed, whereas no effect occurred after treatment with diisopropyl fluorophosphate, p-chloromercuribenzoate and after dialysis against EDTA. Human renin, too, is inactivated by acetylation, diazo coupling and dinitrobenzoylation. The results indicate that one or several amino groups of the renin molecule are essential for enzymic activity.

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Summary1. Intravenous injection of five Goldblatt units (Gbl.U) of renin, or intravenous infusion of 2-5 ug of angiotensin into nephrectomized rats decreased plasma volume by 22+2% (calculated from the increase of the haematocrit) or by 14+2% (calculated from the increase in protein concentration) within 2 minutes. Fifteen minutes and 60 min after injection or infusion, the plasma volume (calculated from both parameters) was still 10% lower than initially. 2. The initial discrepancy between haematocrit values and plasma protein concentration was. neither due to mobilization of red blood cells (r.b.c.) from the spleen, nor to an increase in r.b.c. volume. 3. The observed decrease in plasma volume was large enough to explain the drinking response to renin and angiotensin. Renin may thus induce or aggravate hypovolaemia rather than signalling its occurrence to hypothalamic receptors.

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