PLASMA RENIN ACTIVITY OF RATS AND RABBITS IMMUNIZED AGAINST ANGIOTENSIN II

SUMMARY 1. Plasma renin activity (PRA) was studied in rats and rabbits actively immunized against angiotensin II (A II). 2. The mean PRA values (in ng angiotensin I/ml per h) were 3.5 (s.e.m. = 0.4) in ten control mock‐immunized rats, and 3.3 (s.e.m. = 0.5) in seven rats having demonstrable sustained immunity to A II. 3. In six unanaesthetized rabbits, the appearance of antibody directed against A II was associated with a 263% increase in PRA during the first week, whereas the PRA of five control mock‐immunized rabbits, tested at the same stage, exhibited no such change. 4. The PRA returned to control values by 3 months in the rabbits immunized against A II, although the antibody titres remained high. 5. The finding of significantly elevated PRA early in the course of production of antibody against A II is consistent with the properties of a negative feedback system, the renin hypersecretion being provoked by partial blockade of the normal inhibitory effect of A II on renin release. However, in chronically immune animals, the PRA is normal.