Consumption offibrinolytic proteins inmenstrual fluid fromwomen withnormalmenstrual bloodloss

complexes were present, but little fibrinolytically active plasmin remained. Nodifference was observed between days1and2 ofmenstruation. Thefluidity ofmenstrual discharge hasintrigued investigators formany years,'2andtheabsence of clottable fibrinogen hasbeenattributed tohigh fibrinolytic activity. Thepresenceofplasminogen activator inendometrial tissue3 andthepossibility that anincreased level ofthis enzyme isanaetiologicalfactor inmenorrhagia haveledtotheuse of synthetic antifibrinolytic agentstoreduce excessive menstrual bloodloss.4 Sincethese reports themolecular control ofthe fibrinolytic enzyme systemhasbeenexplored in detail.5 6 Plasmin, themajorfibrinolytic protease, is generated fromtheinactive proenzymeplasminogen bytheaction oftheenzyme plasminogen activator, present onlyintraceamountsinperipheral blood.' 8 Theaction ofplasmin on fibrin(ogen) isregulated by theinhibitors fastacting a2-antiplasmin andslow acting a2-macroglobulin.' '0Fibrin, theprimary substrate ofplasmin, also plays an important regulatory role: bothplasminogen activator andplasminogen bindtofibrin, bringing theproteins intocatalytic contact andcausing thegeneration ofplasmin activity. Inaddition, fibrin boundplasmin isprotected froma2-antiplasmin inhibition, localising theproteolytic action ofplasmin-to theimmediate vicinity ofthefibrin clot.5 6 Therecentexploration ofthefibrinolytic enzyme systemhasbeenfacilitated by methodological advances, notably thepreparation ofantibodies to fibrinolytic proteins andthedevelopment oftripeptidechromogenic substrates forfunctional assays. We haveusedthesetechniques to re-examine fibrinolytic proteins inmenstrual fluidcollected fromwomen withnormalmenstrual bloodloss (less