COMPARISON OF VARIOUS PROCEDURES FOR DETERMINING SUCROSE AND INULIN SPACE IN THE DOG1

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Abstract
In comparisons of the various procedures the calibrated infusion, constant infusion to equilibration, and postnephrectomy values agree and are considered to be the most reliable. No single injection method in intact subjects is considered to be acceptable without reservation, even though values agreeing with the above methods are often obtained. The progressive rise in simple dilution space following a single injection, or cessation of constant infusion, of a substance not completely recoverable is ascribed to progressive rather than to immediate destruction or trapping. Expressions are given for calculating such destruction. Added evidence that diffusion equilibrium is achieved within two hours of constant infusion preceded by a priming injection is afforded by the finding that infusion-recovery spaces so obtained agree with those obtained following cessation of a two-hour infusion not preceded by priming, even though in the latter situation the plasma level is still rising slowly at two hours. Since recoveries following injection of known amounts were never complete with either sucrose or inulin, the amount recovered in 5 hours/average per cent recovery in 5 hours is taken as the value to be divided by the plasma water level at equilibrium to give the infusion-recovery space. This is believed to be the most practical valid method now available for use in intact subjects. The major part of the destruction of sucrose following intravenous injection in the dog is made possible through inversion in the kidneys.