A Comparison of the Relative Effectiveness of Hydropenia and of Pitressin® in Producing a Concentrated Urine12

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Abstract
Giving Pitressin (beta-hypophamine) in supramaximal amounts to hydrated man and dog resulted in urine osmolarities somewhat less than in hydropenic subjects at comparable rates of urine flow. The discrepancy was reduced when the lower plasma osmolarity of th ydrated subject was taken into account. When data obtained under conditions of solute diuresis were expressed in terms of the osmotic U/P ratio or the urine-plasma osmotic pressure difference, values for hydropenic and hydrated-Pitressin conditions were comparable. In the absence of solute diuresis, particularly in man, less consistent results were obtained. Urine-plasma osmotic differentials approached hydropenic values much more slowly than when Pitressin was given during solute diuresis and in several experiments in which Pitressin was present in circulating fluids for prolonged periods, maximal values were never attained. On the other hand, water ingestion by the hydropenic subject receiving Pitressin did not lower the osmotic differential. The reason for these inconsistencies is not known.

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