Pressure-dependent factors in edema formation in canine forelimbs

Acetycholine (10 mug/min) infused intra-arterially for 30 minutes into naturally perfused forelimbs increased forelimb weight 23 g. largely due to edema formation. The weight gain was associated with markedly elevated skin and skeletal muscle blood flows and small vein pressures, suggesting that the edema was attributable, in part, to a rise in microvascular pressures. Mechanically increasing venous pressure and blood flow to similar levels for 30 minutes in pump-perfused forelimbs produced a weight gain of 27 g. The rate of weight gain for the acetylcholine and mechanical alterations was nearly identical. Acetylcholine and mechanical alterations both increased forelimb lymph flow rate but failed to increase lymph total protein concentration significantly. These studies indicate that in the dog forelimb elevated microvascular pressures result in edema formation by increasing the transcapillary hydrostatic pressure gradient without producing an important decrease in the transcapillary colloid osmotic pressure gradient. Increased pressure is not associated with a large increase in microvascular permeability to plasma proteins as is seen with the administration of high doses of histamine and bradykinin.