STRUCTURAL AND FUNCTIONAL COMPARISON OF HDL FROM HOMOLOGOUS HUMAN PLASMA AND FOLLICULAR-FLUID - A MODEL FOR EXTRAVASCULAR FLUID

In the preovulatory period, follicular fluid contains only HDL. Bioche mical characterization of such lipoproteins showed that follicular flu id HDLs were cholesterol-poor particles compared with serum HDLs, wher eas the amount of phospholipids, expressed as percent weight, was sign ificantly higher in follicular fluid HDLs (28.5%) than in serum HDLs ( 25.0%, P<.05). The amount of apolipoprotein (apo) A-IV per apo A-I was significantly higher in follicular fluid than in serum (0.77 versus 0 .58 mg/g apo A-I, P<.02). To explore the role of HDLs as cholesterol a ccepters in physiological media, we compared the ability of either who le human follicular fluids or homologous sera to promote cellular chol esterol efflux using Fu5AH rat hepatoma cells. At equivalent concentra tions of HDL cholesterol in follicular fluid and in serum, t(1/2) valu es for cholesterol efflux were in the same range. In addition, estimat ed maximal efflux values were not significantly different in follicula r fluid and serum (45.9% and 49.6%, respectively), as were K-m values (0.064 and 0.071 mmol/L HDL cholesterol, respectively). In addition, i solated HDLs displayed the same capacity to promote cellular cholester ol efflux in both media. Thus, the kinetics and dose-response data bet ween these two physiological media showed that HDLs play the major rol e in cellular cholesterol efflux. The rate of cholesterol esterificati on, as measured in the presence of cells, was significantly higher in follicular fluid than in serum at constant HDL cholesterol concentrati ons, whereas the rate of esterified cholesterol transfer toward added LDL was lower. In contrast, in a cell-free system, lecithin:cholestero l acyltransferase activity represented only 26% of that in serum HDL, whereas cholesterol ester transfer protein activities were comparable. In summary, in this particular model, we confirmed the essential role of HDLs as physiological accepters in the removal of cellular cholest erol.