Alterations in uterine and serum esterases in pregnant mammals

Uterine flushings, endometrial extracts, and serum from estrous and pregnant rabbits were analyzed by acrylamide gel electrophoresis for esterase activity. Two bands of enzyme activity in uterine findings were detectable on days 4 through 7 after coitus. No activity was detectable in washings from nonpregnant animals or on days 1 to 3 of pregnancy. Esterase activity was detectable in endometrial extracts of all rabbits. The intensity and complexity of the esterase activity markedly increased on day 3 and persisted through day 7 after coitus, during which time nine to ten electrophoretic bands were apparent, compared with four bands in extracts from estrous animals. Serum from pregnant rabbits showed two basic patterns. High esterase activity, concentrated in four major bands, was seen in some sera, while other serum samples showed little esterase activity. No consistent correlation was apparent, however, between the stage of gestation and the serum esterase pattern. In contrast, analysis of mouse serum prior to and after mating showed consistent, reproducible changes in esterase profiles, noticeable about 7 days after coitus and becoming increasingly pronounced until parturition. Changes in mouse serum included both marked enhancement of some esterase activities and concomitant diminution in others with increasing gestation time.