Renin immunocytochemistry of the differentiating juxtaglomerular apparatus.

The differentiation of the juxtaglomerular apparatus in fetuses and newborn mice was investigated by renin immunocytochemistry and electron microscopy. Three to four days before delivery and prior to other organs renin was found in the fetal kidney. At this early time immunoreactivity was preferentially located in cells of the media of interlobular arteries. In newborn mice the formation of new nephrons and maturation of their glomeruli was accompanied by a shift in renin localization from the interlobular arteries to the afferent arterioles. At the same time, kidney renin content and concentration increased rapidly. Synchronously with renin immunoreactivity, during the capillary loop stage of glomerular development, granulated epitheloid cells became visible in the afferent arteriole.