A working model of the perfect osmometer hypothesis in anuria.

This communication contains a model describing osmotic phenomena that result from an osmotic disturbance (gain or loss of non-isotonic solutions from the extracellular compartment), if cells function as perfect osmometers. This model (a) predicts the changes in extracellular water and in solute concentration, if the magnitude of the disturbance is known; (b) computes the amount of a solution of a given osmolality necessary to create a desired change in extracellular water; (c) estimates, by osmometric calculations, initial extracellular and total body water; (d) estimates the 'new' solute that is created by anuria and by dilution of extracellular solute controlled by hormonal feedback. Anuria and extracellular expansion are experimental conditions usually accompanying the osmotic disturbance. The model is, therefore, suitable for precise in vivo studies of osmotic disturbances.