Renin synthesisin vivois feedback regulated by the plasma angiotensin II concentration, the intrarenal pressure, the salt loading of the organism and the macula densa mechanism. At the level of renal juxtaglomerular cells renin synthesis is regulated by cyclic AMP, by nitric oxide and by the cytosolic calcium concentration. Cyclic AMP and nitric oxide are stimulators, whereas calcium is an inhibitor of renin synthesis.