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

Seven types of procedures have been used for determining volume of distribution (space) as an estimate of extracellular fluid (ECF). These are: (a) infusion-recovery, with infusion continu-ing until equilibration (as indicated by constant plasma level and by failure of further infusion to change space) is achieved (1); (b) calibrated in-fusion continuing until constant space is achieved (2); (c) injection-extrapolation, i.e., extrapola-tion of falling plasma curve to zero time following a single injection in intact (3) or nephrectomized (4) subjects; (d) simple dilution spaces following a single injection as recovered minus excreted/ plasma level (5), or as injected minus excreted/ plasma level (6, 7); (e) renal clearance/slope, i.e., following a single injection of substances which are completely recovered in the urine (re-nal clearance equals total clearance) and whose falling plasma curve is a straight semilog line, as renal clearance in a period/change in natural logarithm of plasma level in that period (8); (f) total clearance/slope, i.e., following a calibrated infusion permitting calculation of total clearance, as total clearance/change in the natural logarithm of plasma level (9); (g) differential clearance, as amount excreted in a period/change in plasma level in that period, following a single injection (10). With procedure (a), using a substance previ-ously shown to be completely recovered, the space is calculated as amount recovered following ter-mination of infusion/concentration in plasma wa-ter (ECF) shortly before termination. Equili-bration is hastened by a priming injection. With procedure (b) a completely recoverable substance is infused without priming. Amount present in subject at time t is taken as amount infused minus amount excreted up to time t. This is divided by concentration in plasma water (ECF) to ge