The Quantification of Renin Liberated in Vitro from Rat Kidney Slices 1

Summary

A bioassay system for the determination of renin liberated in vitro from surviving rat kidney slices incubated in Warburg vessels is described. The system is based on zero-order enzyme kinetics obtained by incubating rat renin with concentrated dog renin substrate to obtain a K ₀ for the heterologous enzyme-substrate reaction. The method is accurate over a 1000-fold range of renin concentration from 0.03 to 0.00003 GU/ml which encompasses renin concentrations in incubation media and in rat kidney slices. Preliminary results indicate the liberation of renin in vitro is metabolically dependent and amounts to about 5% of the renin content of the slice during a 2-hr incubation period. The rate of liberation of renin from slices of rat kidneys obtained from rats on a sodium free diet was several times the rate found for slices taken from controls on a normal diet.