CHARACTERIZATION AND HORMONAL MODULATION OF ANTICOAGULANT HEPARAN-SULFATE PROTEOGLYCANS SYNTHESIZED BY RAT OVARIAN GRANULOSA-CELLS

Anticoagulant heparan sulfate proteoglycans endow the vascular endothe lium with antithrombotic properties, but their role outside the vascul ar bed is unknown. Granulosa cells form an avascular compartment in th e ovarian follicle, in which a heparin-like activity has been describe d. At ovulation extravascular coagulation occurs around ovulatory foll icles, and after expulsion of the oocyte, a fibrin clot forms in the a ntral cavity. Granulosa cells synthesize two major heparan sulfate pro teoglycans, whose anticoagulant nature has not been investigated. The purpose of this study was to characterize anticoagulant heparan sulfat e proteoglycans synthesized by rat ovarian granulosa cells. Affinity p urified S-35-labeled anticoagulant heparan sulfate glycosaminoglycans represent 6.5% of the total heparan sulfate synthesized, and they cont ain 13% 3-O-sulfated disaccharides that are markers of the antithrombi n-binding site of heparin. The biological activity of granulosa cell h eparan sulfate proteoglycans was demonstrated by their ability to bind antithrombin and to accelerate the formation of thrombin-antithrombin complexes. The impact of hormonal stimulation on granulosa cell antic oagulant heparan sulfate proteoglycans was studied using I-125-antithr ombin binding assays. Follicle-stimulating hormone induced a redistrib ution of anticoagulant heparan sulfate proteoglycans from the granulos a cell layer to the culture medium, indicating that their distribution could be modulated according to the stage of follicular development. These results suggest that anticoagulant heparan sulfate might be crit ically located in the follicle to maintain fluidity around the oocyte until its expulsion at ovulation.