The interstitial space of adipose tissue as determined by single injection and equilibration techniques

The interstitial 14C-sucrose space was determined in the subsutaneous adipose tissue of the dog using both a single injection-indicator dilution technique and an equilibration-tissue sampling method. 131I-albumin and 51Cr-labelled erythrocytes served as intravascular indicators. The conventional extrapolation method for single injection curves yielded space values several times lower than those measured by the equilibration technique, although sampling was continued until the venous outflow samples contained less than 1% of the peak 14C-sucrose activity. This discrepancy may be due to long transit times, for which the conventional extrapolation procedure does not account. An extrapolation procedure is proposed based on the assumption that the area under the normalized extra- and intravascular curves should be equal. By this procedure as well as by the equilibration technique the interstitial 14C-sucrose space in adipose tissue measures approximately 10 mlX100 g-1. The single injection technique does not appear applicable for space determinations in adipose tissue during sympathetic nerve stimulation (3-7 Hz), possibly due to "trapping" of the tracers within the tissue.