1. By the use of a mechanical graded sieving technique a high yield of isolated glomeruli has been obtained from rat kidney.
2. Microscopy and renin assay have shown the presence of renin-containing juxtaglomerular cells attached to these glomeruli.
3. The viability of isolated glomeruli has been confirmed by the ability of the cells to survive and divide in tissue culture and by their exclusion of vital dyes.
4. In superfusion after washout of extracellular renin, the glomeruli actively release constant amounts of renin over 3 h in direct proportion to the number superfused.
5. Decreasing sodium concentration from 140 to 110 mol/l with constant osmolarity of 305 mosmol/l stimulated renin release by a direct effect on juxtaglomerular cells.
6. Catecholamines stimulated renin release in vitro in proportion to the potency of their action on β-adrenoreceptors.
7. The system of superfusion of isolated glomeruli provides a technique for studying the influence of mediators leading to renin release acting directly on juxtaglomerular cells, independent of pressure change, tubular sodium, the sympathetic nervous system and circulating hormones.