Disappearance of dextran 70,000 from plasma of hamadryas baboons

Evans Blue (EB), [131I]human albumin and [14C]dextran 70,000 were injected into three water repleted and water depleted hamadryas baboons, in order to evaluate the permeability of their capillary bed under these conditions. The rate of disappearance of dextran from the plasma is significantly higher than that of the other markers, despite its relatively high molecular weight. Half-life values of EB and albumin in water depleted baboons were significantly higher than values in water repleted animals. Inulin and dextran showed no significant difference before or after dehydration. Chromatography of urine and plasma samples on columns of Sephadex G-75 showed that dextran passed the glomerular capillaries and is excreted into the urine with its same original molecular size. The permeability of capillary beds to dextran 70,000 is negligible. The fact that the kidneys excrete dextran means that dextran 70,000 is not a useful marker for calculating the capillary permeability in hamadryas baboons.