FOLLICULAR-FLUID LIPOPROTEINS IN THE MARE - EVALUATION OF HDL TRANSFER FROM PLASMA TO FOLLICULAR-FLUID

Using a density gradient ultracentrifugal procedure, we have separated equine plasma and follicular fluid high-density lipoproteins (HDL). T he density distribution of the follicular fluid HDL was clearly displa ced towards the highest densities in comparison with that of plasma HD L. Similarly, an analysis of size distributions showed a decrease in f ollicular fluid HDL diameters (4.2 to 9.2 nm) compared to plasma HDL ( 5.5 to 9.5 nm). HDL were isolated into three subfractions on the basis of the disposition of the Sudan Black stained bands in the centrifuge tubes. Concentrations of each subfraction were clearly lower in the f ollicular fluid, and the relative percentages with regard to the plasm a equivalents were inversely proportional to the molecular weights (23 .8% for HDL-1, 49.9% for HDL-2 and 63.7% for HDL-3). The cholesterol/p hospholipid molar ratio and the esterified/free cholesterol molar rati o were clearly increased in the follicular HDL-2 and HDL-3 subfraction s. The apolipoprotein distribution in follicular fluid HDL was very cl ose to that in plasma HDL. LCAT activity measured in human as well as equine samples was weaker in follicular fluid compared to plasma in bo th species (4.0 nmol of free cholesterol esterified per h per ml vs. 2 4 nmol per h per ml). Theoretical concentrations of follicular fluid H DL were calculated assuming that the HDL particles would be merely a f iltration product undergoing no detectable metabolic modifications. Bi ochemical measurements showed that the lightest particules (HDL-1) wer e less numerous than suggested by the theoretical calculation. Thus, a lthough follicular fluid HDL appear to be a filtration product of plas ma HDL, they undergo metabolic transformations that we suggest may be linked to hormonal synthesis and reverse cholesterol transport.