Mechanisms for redistribution of plasma protein following acute protein depletion

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Abstract
Acute plasma protein depletion is followed by a rapid and substantial replenishment of the protein deficit. We studied the effects of plasmapheresis on flow and composition of peripheral lymph in 11 unanesthetized sheep. Whole blood was replaced with red blood cells and lactated Ringer solution to reduce plasma protein concentration ([P]) 26-54%. At 24 h after plasmapheresis, [P] had returned halfway to base line. Lymph flow (L) increased immediately after plasma protein reduction, was maximal 3 h later, and remained elevated for more than 3 days. The increase in L was coupled with a decrease more than 3 days. The increase in L was coupled with a decrease in lymph-to-plasma protein concentration ratio ([L/P]). The plasma-to-lymph oncotic gradient was reestablished by 24 h due to the reduction in lymph protein and the partial return of [P]. After 24 h, L remained elevated despite base-line levels for all measured vascular pressures and plasma-to-lymph oncotic gradients. Although lymph flow was increased, the permeability-surface area product for protein was decreased below base line. The data confirm that the partial return of [P] in the first day after plasmapheresis is due largely to a shift of extravascular protein mass into the vascular compartment and show that redistribution is initiated by increased lymphatic return and maintained by a sustained increase in L and a decrease in protein permeability of the plasma-lymph barrier.