BIOLOGY OF REPRODUCTION 36,1289-1295 (1987) Activation of Plasminogen by the Early Bovine Embryo’

Activation of the plasma zymogen plasminogen to the enzyme plasmin by the early bovine embryo was evaluated. Skteen-cell embryos to early morulae were collected at death f rom handmated synchronized and superovulated crossbred beef cows. Embryos were cultured in Ham’s F-12 medium supplemented with 15 mg/ml bovine serum albumin containing 0, 15, 30, 60 or 120 pg/ml plasminogen in a humidified atmosphere of 5 % COz in air at 37OC. Cultures were observed every day, and stage o f development was recorded. Medium was collected at 2 4 4 intervals, starting at initiation and continuing thro’ugh 288 h of culture. Plasminogen ac-tivator and plasmin levels in the culture media were determined, using a caseinolytic assay. The percentages of embryos developing to the initiating hatching blastocyst, hatched blastocyst, attached blastocyst, and attached blastocyst with trophoblastic outgrowth stages were not significantly different between the five levels of plas-minogen. Initiation and completion of hatching, however, accelerated as plasminogen concentration increased in the culture media. Plasminogen activator production, expressed as milliunits*ml- ‘- h- ’.viable embryo-’, was low for the first 48 h of culture, increased between 48-120 h, and tended to plateau thereafter. Plasminogen activation, measured indirectly as the plasmin concentration in a microdrop o f medium and expressed as pg plasmin-ml- ’.h- ’.viable embryo-’, followed plasminogen activator production, and was consistently low fo