ESTIMATION OF REFERENCE SPACES IN THE PERFUSED RAT HINDLIMB

The isolated perfused rat hindlimb offers a suitable preparation for the development of a physiological-based pharmacokinetic model of drug distribution in non-metabolising tissues. These tissues (skeletal muscle, skin bone and adipose) together represent 73% body weight in man. Standard markers (Cr-51-RBC, C-14-sucrose, H-3-water) were used to estimate the physiological reference spaces in the preparation using the indicator dilution technique; the distribution of I-125-albumin and C-14-urea was also investigated. The hindlimb of female rats (n=5-9) was perfused in a single pass mode at 25 degrees C using Krebs-Hensleit buffer with 2% BSA at 4 ml/min (Q). The markers were administered individually as a bolus (30 much greater than 1) in a random order via the aortic cannula with fractional venous collection. Mean transit times (MIT) were calculated using statistical moment analysis, corrected for the time spent in the catheters, and the volumes of distribution obtained (Q.MIT). The mean intravascular volume represented 4.1%, interstitial volume 23.6% and intracellular volume 22.4% wet weight of the hindlimb. The volume occupied by albumin was significantly greater than that of RBCs (P<0.025). It was, however, excluded from 59.1% of the interstitial space. Urea did not occupy the full aqueous volume.