The effect of variations in solute excretion and vasopressin dosage on the excretion of water in the dog.

It has been known for some time that osmotic diuretics may modify the effect of vasopressin on urine concentration (1, 2). However, it has been generally assumed that urine will remain hypertonic to plasma if sufficient hormone is administered irrespective of the extent of the solute diuresis. This conclusion was based on the thesis that the major action of vasopressin is to promote the elaboration of a hypertonic urine presumably by a process involving active water reabsorption. Smith (3) and Wesson and Anslow (4), on the other hand, have suggested that vasopressin increases permeability of the tubule membrane to water in the distal segment, permitting osmotic equilibration in this area, and thereby diminishing the volume of isosmotic fluid delivered to a hypothetical concentrating site in the collecting duct. The experiments to be reported were designed to reexamine in a quantitative fashion the effect of solute excretion on the renal response to purified arginine vasopressin. The data have been interpreted in the light of present information concerning the probable mode and sites of action of the hormone.