EVIDENCE IN MAN THAT URINARY ELECTROLYTE LOSS INDUCED BY PITRESSIN IS A FUNCTION OF WATER RETENTION 1

Abstract

The effects of a long-acting posterior pituitary extract on electrolyte and water excretion were studied in man. Observations were made during twenty 2- to 4-day periods of Pitressin (1 unit/12 hrs.) in 9 subjects maintained on constant diets and fluid intakes. Pitressin produced in normally hydrated subjects prompt water retention and resulting weight gain, serum dilution and increased urinary Na and chloride on the 2d and 3d day of Pitressin admn. Cessation of hormone reversed these changes, and fluid restriction during Pitressin admn. prevents the effect. The renal loss of Na and chloride resulting from obligatory retention of water is interpreted as a homeostatic response to over-expansion of fluid volume.