Renal adaptation and gut hormone release during sodium restriction in ileostomized man

1. The renal excretion of water, electrolytes, aldosterone and kallikrein was monitored in 12 ileostomized patients before and during sodium deprivation. Changes in plasma renin activity (PRA), plasma aldosterone and plasma arginine vasopressin (AVP) concentrations were measured, together with aldosterone in ileal fluid. The pattern of gut peptide release in response to a test meal was also examined to assess whether a circulating gut peptide might be involved in the renal adaptation to sodium restriction, and compared with healthy normal subjects who were under no dietary constraint. 2. In each patient renal sodium excretion fell within 8–12 h of sodium deprivation and was associated with a prompt and significant rise in PRA; much later increases in plasma aldosterone concentration and renal aldosterone excretion occurred, and were established by day 2 of sodium restriction. No consistent change in renal kallikrein excretion was found. 3. Ileal sodium loss was little changed by sodium deprivation, but ileal potassium concentration rose steadily and became significantly correlated with PRA, and to a lesser extent with renal aldosterone excretion. 4. Of the gut peptides measured in plasma, only the insulin profile was altered by sodium deprivation, with an increase in the test meal response; insulin has previously been shown to have a significant antinatriuretic action at physiological concentrations. Plasma levels of pancreatic polypeptide and motilin were increased in ileostomized patients when compared with normal subjects, but were unaffected by the change to a low sodium diet. 5. An early increase in urine flow and water diuresis occurred during sodium deprivation, following a cyclical pattern with peaks each evening. There were no corresponding changes in measured plasma AVP concentration or creatinine clearance. This observation remains unexplained.