The effect of vasopressin on solute and water excretion during and after surgical operations.

The relationship between the concentration of plasma arginine vasopressin (AVP), urine volume, and osmolality during and after an abdominal operation was studied in nine patients. In all patients the AVP level rose well above that necessary for maximal antidiuresis (5 fmol ml-1) and then returned to within the normal range (0.5-5.0 fmol ml-1) usually over the next 24 hours. During this period of raised AVP concentration the urine volume, which varied considerably, was closely related to osmolar excretion. With the fall of AVP to normal levels, all but one of the patients eventually exhibited positive free water clearance. However, in most patients the urine remained hypertonic for some hours and its volume continued to be determined mainly by osmolar load which was itself apparently related to glomerular filtration rate. At no time was there a significant relationship between changes in plasma AVP concentration and urinary volume.