Effects on Renal Water and Sodium Excretion of Infusions of either Iso‐Osmolar Saline or a Hypo‐Osmolar Solution of Non‐Electrolytes

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Abstract
The effects of iso‐osmolar and hypo‐osmolar volume expansion on renal water and sodium excretion were studied in dogs during light chloralose anesthesia. Saline or a hypo‐osmolar solution of glucose and urea was given i.v. (20 ml/kg b.wt. in 60 min). From the start of this infusion the combined weight of the hydration infusate and the dog was maintained constant by a servo system, which controlled the rate of infusion of a hypo‐osmolar solution. Consequently the degree of hydration increased linearly during the infusion period after which it remained constant throughout the experiment. No increase in free water clearance was seen after iso‐osmolar volume expansion. The rate of excretion of sodium increased considerably. Hypo‐osmolar volume expansion provoked a water diuresis during which the rate of excretion of sodium fell to less than 0.1 μmol/kg b.wt. min. It is concluded that under the present circumstances infusion of iso‐osmolar saline is not associated with a decrease in the rate of secretion of vasopressin.