Investigation of the fibrinolytic system during nonpregnant and pregnant oestrous cycles of bitches.

The fibrinolytic system was studied during the oestrous cycle of nonpregnant (n = 12) and pregnant (n = 12) bitches. Blood samples were taken during late pro-oestrus, at ovulation, at days 1, 5, 10, 15, 20, 25, 30, 40, 50, 60, 90 and 120 of metoestrus, and during anoestrus. The concentrations of fibrinogen and fibrin(ogen) degradation products, the euglobulin lysis time, the activities of plasminogen and alpha 2-plasmin inhibitor and the haematocrit were determined. Concentrations of oestradiol and progesterone were measured in additional blood samples in late pro-oestrus, at ovulation, at days 30, 60, 90 and 120 of metoestrus, and in anoestrus, for retrospective control of oestrous cycle stages. In the pregnant bitches, significantly higher values (P < 0.05) were found for the concentrations of fibrinogen and fibrin(ogen) degradation products from day 15 to day 60, for the euglobulin lysis time from day 20 to day 50, for the plasminogen activity from day 15 to day 40 and for the alpha 2-plasmin inhibitor activity from day 20 to day 30 of metoestrus compared with values for nonpregnant bitches. The significant increase in fibrinogen concentrations observed in the pregnant bitches is thought to be a local reaction of the coagulation system due to alterations of the uterine epithelium and endothelium induced by placentation. The slight increase in the concentration of fibrin(ogen) degradation product combined with the slight increase in the activities of plasminogen and alpha 2-plasmin inhibitor are indicative of a local rather than systemic hyperfibrinolysis during canine pregnancy. The prolonged euglobulin lysis time, which is indicative of decreased fibrinolytic activity in pregnancy, is thought to be a laboratory artefact caused by increased fibrinogen concentrations.