Renin measurement in blood collected from the efferent arteriole of the kidney of the rat.

Plasma renin could be detected in 16 nl of rat plasma by incubating at 50 degrees C, pH 6.2 with 20 mul of a rat renin substrate. In 60 nl samples it could be estimated and differences in concentration of 20% could be detected. Plasma renin concentration was measured in blood from the superficial efferent arterioles of a rat's kidney. The concentration of renin in different efferent arterioles of the same rat were similar. The renin concentration of efferent arteriolar blood was 361 plus or (-1)89 (S.D.) ng Al ml minus 1 (blood) hour (-1) which was not different from the renin concentration of simultaneously taken femoral artery blood (340 +/- 217). Plasma concentration can be measured in efferent arteriolar blood and will allow the control of renin secretion to be studied.