Effects of cold on vascular permeability and edema formation in the isolated cat limb

We investigated the effects of cold temperatures on microvascular protein permeability in the isolated constant-flow perfused cat hindlimb. The perfusates were 20% cat plasma-80% albumin-electrolyte solution (low-viscosity perfusate, approximately 1 cP) or whole blood (high-viscosity perfusate, approximately 4 cP). The time at low temperature (less than 10 degrees C) was less than 3 h (short term) or greater than 5 h (long term). Decreases in the solvent drag reflection coefficient (sigma f) indicated increases in permeability. The sigma f's were determined with the integral-mass balance method from measurement of changes in protein concentration and hematocrit induced by fluid filtration into the tissues. Short-term cold exposure did not increase permeability with either a low- or a high-viscosity perfusate, whereas long-term exposure with limb temperatures of approximately 5 degrees C significantly increased permeability when the perfusate was whole blood. In addition, we verified our previous prediction that flow had to be reduced to 6-8 ml.min-1.100 g-1 to avoid the hydrostatic edema caused by short-term perfusion with whole blood at approximately 5 degrees C. Also, we found that at approximately 3 degrees C histamine's permeability-increasing effect was totally abolished, whereas at approximately 20 degrees C this effect was partially inhibited. Hence, constant-flow perfusion at low temperature with whole blood can cause edema by a pressure-dependent mechanism, whereas long-term perfusion with this perfusate at low temperatures can cause a permeability increase that further compounds edema formation. Histamine is not responsible for this permeability increase.