[A compartment analysis of the significance of extracellular fluid volume for body fluid dynamics]

The curve of a reduction in plasma concentration of the indicator substance creatinine for a period of 120 to 240 min was investigated after single intravenous administration of creatinine in a dose of 150 mg/kg on dogs. A model for two compartment distribution of the indicator substance was used as the first compartment was intravasal, but the second--interstitial space of body fluids. The following parameters were estimated: renal clearance, volume of distribution, glomerular filtration, intercompartment clearance and velocity constants of transport between the two compartments. An increase of the volume of extracellular fluid (ECF) was induced by intravenous infusion of 2% of sodium chloride solution in the amount of 30 ml/kg. A reduction in the volume of ECF was caused by peritoneal dialysis with isotonic solution of glucose in the amount of 5% of the body mass. After an increase of the volume of ECF there was an increase in the volume of distribution, elevation of glomerular filtration and a reduction in the velocity constant of transport from the intravasal to interstitial fluid. There was a reduction in the volume of distribution, limitation of glomerular filtration and increment of velocity constant of the transport. The established changes in the velocity constants of the transport showed changes in the dynamics of body fluids, which could be due to vasoconstriction or vasodilation as a mechanism of myogenic autoregulation during changes in the volume of ECF.