Presence of an Inhibitor of Plasminogen Activator in Uterine Fluid of the Western Spotted Skunk During Delayed Implantation

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Abstract
The hypothesis that protease inhibitors would be present in uterine fluids of the western spotted skunk during the period of delayed implantation but would decline or disappear during implantation was tested. Blood plasma, uterine flushings and medium from endometrial cultures were collected 40-70 days preimplantation (Stage 1), 20-25 days preimplantation (Stage 2), 1-3 days preimplantation (Stage 3) and 1-5 days postimplantation (Stage 4). Protein content of the flushings was low in Stage 1 (12.9 .+-. 3.0 .mu.g), increased slightly (21.8 .+-. 6.4 .mu.g) during Stage 2 and increased markedly in Stages 3 (99 .+-. 44.8 .mu.g) and 4 (256 .+-. 150 .mu.g). No protease activity was detected in any fluid at any stage. Uterine flushings, however, contained an inhibitor of plasminogen activator (PA) of apparent MW .apprx. 70,000. The total amount of inhibitor increased as pregnancy progressed, but specific inhibitory activity was highest during Stages 1 and 2 (1.7 and 3.2 units/.mu.g protein, respectively) and declined in Stages 3 and 4 (1.2 and 0.6 units/.mu.g protein, respectively). The inhibitor was present in medium from uterine cultures but was low in plasma. All of the fluids could inhibit trypsin, but not plasmin. The antitrypsin activity in uterine fluids is attributed to plasma transudate. An inhibitor of PA in skunk uterine fluids is demonstrated, but no temporal relationship between its presence and the period of obligate delay of implantation was observed.