Vascular and tubular renin in the kidneys of mice

Monospecific antisera and the immunocytochemical PAP-method have been used to localize renin in the kidneys of mice. With this procedure, reaction product was not only observed in the epitheloid cells of kidney vessels but also in kidney tubules: in the apical portion of proximal tubule cells and in some cells of the connecting and the cortical collecting tubule. To answer the question, whether the occurrence of renin in kidney tubule cells is the consequence of tubular synthesis or that of glomerular filtration of plasma renin followed by its uptake from the tubular lumen, tracer experiments with radioiodinated renin and with horseradish peroxidase were undertaken. The results of these studies as well as other arguments suggest reabsorptive pinocytosis of the filtered hormone as the source of tubular renin.