[Cellular and intrarenal aspects of renin secretion]

Renin is synthesized, stored and excreted from cells (JG cells) localized in the afferent glomerular arteriole. Preprorenin is formed first by biosynthesis. After splitting off of the pre-fraction, glycosylering and passage through the Golgi apparatus, prorenin, which is biologically inactive, may be excreted immediately or be stored in secretory granules where activation occurs by splitting off of the pro-fraction. Excretion of the secretory granules is regulated and takes place by exocytosis. Important intracellular signal molecules include, inter alii, calcium which is inhibitory and cyclic AMP which stimulates release. In addition, osmotic water movements also play an important role. The physiological regulatory mechanisms include 1) a baroreceptor: lowered perfusion pressure to the kidney stimulates release of renin, 2) a tubular signal: decrease in Cl(-)-concentration at the macula densa stimulates release of renin, 3) the nerve supply of the kidney which stimulates directly via beta-receptors on the JG cells and also indirectly via alpha-adrenergic influence on haemodynamic and tubular resorption and 4) local and circulating hormones, particularly angiotensin II and prostaglandins.