Uterine peptidase activity in the rat and rabbit during pseudopregnancy.

Uterine peptidase levels in the rat and rabbit were determined during the estrous cycle and pseudopregnancy. During the estrous cycle higher peptidase activity was found in rat uterine homogenate and uterine fluid at the proestrous and estrous stages. Highest peptidase levels were found in rat uterine homogenate and in rabbit endometrium during pseudopregnancy, a peak being reached at the stage of implantation. The peptidase activity of rabbit fallopian tube homogenate was essentially constant during pseudopregnancy. These findings indicate that uterine peptidase activity changes in response to change in estrogen and progesterone levels. No such change is shown by the fallopian tube peptidases. Maximal activity at implantation may reflect preparative changes of the uterus for reception and implantation blastocysts.