Impaired control of renal hemodynamics and renin release during hyperkalemia in rabbits

We analyzed the changes in control of renal hemodynamics and renin release resulting from hyperkalemia in the rabbit. Plasma potassium activity was maintained at a controlled elevated level by intravenous infusion of KCl. The potassium activity of the control group (n = 23) averaged 3.20 +/- 0.06 meq/l and that of the hyperkalemic group (n = 13) averaged 5.80 +/- 0.13 meq/l. Renal blood flow (RBF), glomerular filtration rate (GFR), and renin release were measured over a range of renal perfusion pressures achieved by constriction of the suprarenal aorta. The control group's RBF and GFR exhibited excellent autoregulatory capability from 100 to 80 mmHg. However, significant impairment of autoregulation was apparent in the hyperkalemic group. At 100 mmHg, RBF and GFR in the hyperkalemic group averaged 33 and 34% greater, respectively, than those of the control group (P less than 0.005); both variables in the hyperkalemic group were greater than the values of the control group over the autoregulatory range (100-80 mmHg). The renin release values for the two groups were not different at the 100-mmHg pressure level, although renin release of the hyperkalemic group increased to higher levels than those of the control group as perfusion pressure was reduced. At the 70- and 60-mmHg levels renin release from the hyperkalemic group averaged approximately 300% greater than that of the control group (P less than 0.05). However, when expressed as percentage change, the stimulatory effect of hyperkalemia was not apparent.(ABSTRACT TRUNCATED AT 250 WORDS)