Blood-to-tissue clearance vs. lymph analysis in determining capillary transport characteristics for albumin in skin.

The blood-to-tissue clearance of radioactive albumin and a lymphatic flux analysis were used to evaluate the transport properties of albumin in the canine hindpaw. A prenodal lymphatic was cannulated, and lymph was collected for a 2-h control period. Thereafter venous pressure was elevated between 7 and 31 mmHg. After 2 h of increased venous pressure, the radioactive tracer was given intravenously. During the next 2 h lymph was sampled, and at the end of this time tissue and blood samples were obtained. The experiments showed that, of the tracer filtered in excess of control at increased venous pressure, an estimated 21% was cleared via the lymphatics and 79% was retained in the tissue. As a percentage of total tracer flux at increased venous pressure, 9% (measured) was drained by lymph and 91% was retained in the tissue. Of the fluid filtered in excess of control at increased capillary pressure, 70% (measured) was drained via the lymphatics and 30% was retained in the tissue in the same period. Twice the amount of endogenous albumin filtered across the capillary wall was drained via the lymphatics during the experimental period. The lymphatic washout of endogenous albumin from the interstitium will cause an underestimation of the capillary reflection coefficient and overestimation of the permeability-surface area product. Because of the loss of tracer from the tissue, the opposite occurs when the blood-to-tissue clearance of radioactive albumin is used.