[Renin-angiotensin-aldosterone system in diabetes insipidus]

Plasma renin activity (PR) and plasma aldosterone level (PA) were investigated in 38 patients with central diabetes incipidus under conditions of standard sodium intake and after a three-day reduction of sodium in the diet with an additional furosemide load. Blood was recovered for examination in the morning under complete rest and after a two-hour slow walk. Apparently healthy volunteers (20) served as control. The PR and PA content was determined by the radioimmunological method. Not only the basic, but also the stimulated renin secretion was increased in patients with diabetes incipidus. The basic PA level was significantly diminished; after stimulation its level did not differ from that in healthy persons. At rest and with decreased sodium intake the patients displayed two types of PR activity: in some (n=18) there was no elevation, and in other (n=19) the rise was marked. It is supposed that in diabetes incipidus hyperreninemia was compensatory, directed to water retention in the organism; apparently it participated in the mechanism of hypovolemic thirst. An unusual combination of increased PR with diminished PA level is described for the first time.