THE EFFECT OF VARIATIONS IN SOLUTE EXCRETION AND VASOPRESSIN DOSAGE ON THE EXCRETION ON WATER IN THE DOG

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Abstract
The administration of varying doses of purified vasopressin during combined water and solute diuresis in dogs results in a progressive decline in CH2O de- pendent on the dosage of hormone. The graded effect is such that at low rates of vasopressin administration a transition from hypertonic to hypotonic urine is noted as solute excretion rises. This transition may be reversed with maximally effective dosages of the hormone. The data have been interpreted in the light of the thesis that vasopressin affects tubule membrane permeability in a graded fashion throughout the distal segment, both in the area where free water is present and in the terminal concentrating site. Osmotic equilibration of tubule fluid with renal interstitial tissue is essential for the elaboration of hypertonic urine. Since solute excretion and vasopressin exert opposing effects on the movement of water out of the tubule lumen into the interstitial space, net movement of water and the final urinary solute concentration are dependent on the relative contribution of each of these factors to the overall process.