Acute Effects of the Administration of Vasopressin During Water Diuresis in the Dog*

It is generally accepted that the elaboration of a urine hypertonic to plasma by the mammalian kidney occurs by means of the abstraction of water from the collecting duct lumen into the medullary interstitium (1). The driving force for the movement of water is an osmotic gradient created by the active transport of sodium chloride from the ascending limb of the loop of Henle into the medullary interstitial space, as originally postulated by Wirz (2) and subsequently confirmed by the micropuncture studies of Gottschalk and Mylle (3). By necessity, micropuncture studies are conducted during essentially steady-state conditions. Similarly. urinary concentrating ability is customarily evaluated during the state of hydropenia or at graded levels of osmotic diuresis, but in either case, at maximally effective circulating levels of vasopressin. Few data exist on the precise changes in urinary composition during the achievement of the antidiuretic state. It was postulated that such data might provide further information concerning the role of vasopressin in the renal concentrating process. Consequently, in the present study observations have been made on the urinary changes during the