ASSESSMENT OF PROTEIN PERMEABILITY IN NORMAL HUMAN SYSTEMIC CIRCULATION

Vascular permeability to oncotic agents is an important determinant of transvascular fluid flux (J) over dot and systemic fluid balance. In this study, a technique was developed to measure protein reflection co efficients (sigma) for albumin (Alb), immunoglobulin (Ig) G, and IgM i n the intact human systemic circulation to evaluate the role of vascul ar protein permeability in health and disease. A mathematical model wa s developed to calculate a in the forearm circulation from changes in venous hematocrit and protein concentration that occur during edema fo rmation. Assumptions required for the model were Validated in an initi al set of experiments in normal subjects when edema was induced by inf lating a pneumatic cuff on the upper arm. A second series of experimen ts assessed a for Alb, IgG, and IgM in men (n = 7) and in women in the follicular (n = 5) and luteal (n = 4) phases of the menstrual cycle. There was an increasing trend in a with molecular size in aggregated s ubjects [sigma(Alb) = 0.81 +/- 0.12 (SE), sigma(IgG) = 0.88 +/- 0.12, sigma(IgM) = 0.92 +/- 0.18; P = 0.088]. These values were consistent w ith those obtained with in vitro preparations. a values were lower in women in the luteal than in the follicular phase (P = 0.047). We concl ude that the assumptions required for this model can be achieved in th e intact forearm circulation and that there are menstrual phase-relate d differences in vascular protein permeability in normal women.