Detection of kallikrein gene expression and enzymatic activity in porcine endometrium during the estrous cycle and early pregnancy.

Porcine conceptuses rapidly elongate within the uterine horns prior to the period of placental attachment. During the time of elongation, secretion of estrogen by the developing conceptuses occurs for the establishment of pregnancy through maintenance of corpora lutea and facilitation of placental attachment. Factors associated with the uterine luminal epithelium accentuate embryo attachment by allowing close contact between the conceptus and the uterine epithelium. Kallikrein, a serine protease, may be involved with the timing of conceptus expansion and placental attachment to the uterine surface. The objective of this study was to evaluate kallikrein enzymatic activity, protein, and gene expression in the pig during the estrous cycle and early pregnancy. Enzymatic activity was first detected in uterine flushings (UTF) on Day 12 of the estrous cycle and pregnancy. Activity was enhanced on Day 12 of pregnancy compared to that in cyclic gilts, with a reversal of increased kallikrein activity in cyclic compared to pregnant flushings on Day 15. Western blot analysis with antiserum to human plasma kallikrein detected a 50-kDa product similar to human plasma kallikrein from Day 10 to Day 15 of the estrous cycle and pregnancy. Kallikrein enzymatic activity in UTF was associated with the presence of a 23-kDa reactive product. Gene expression of kallikrein as determined by reverse transcription-polymerase chain reaction indicated the presence of kallikrein mRNA in the porcine endometrium and conceptuses. Results indicate that an increase in uterine luminal kallikrein activity occurs during the estrous cycle at a period that corresponds to rapid conceptus elongation during pregnancy of the pig. The present information suggests that kallikrein may play a role in opening the window for establishment of pregnancy in the pig.