THE NORMAL ANTIDIURETIC MECHANISM IN MAN AND DOG; ITS REGULATION BY EXTRACELLULAR FLUID TONICITY 12

Abstract

In normal man and dog, water deprivation causes a slight rise in serum total solute concn. associated with maximal concn. of the urine. Following water admn. there occurs a slight but measurable dilution of the serum. With this the urine becomes progressively more dilute reaching levels distinctly hypotonic to the extracellular fluid. When the admd. water load is excreted,serum and urine total solute concns. again rise. Total solute concn. of serum and urine was measured by use of a thermistor to measure freezing point depression. Furthermore, in the dog, the presence of antidiuretic activity in the serum was demonstrated at the end of the period of water deprivation, while no activity was demonstrable during the diuresis that followed water admn. Serum antidiuretic assays were done on 4 post-hypophysectomized rats using the change in solute concn. of the rats urine following injn. of test serum as the index of antidiuretic activity. The role of the posterior pituitary in this mechanism is indicated by persistence of dilute urine during dehydration in spite of very marked hypertonicity of the serum in a patient with posterior pituitary insufficiency.