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.

The induction of deciduomata in the pseudo-pregnant rat by systemic administration of histamine and histamine releasers

Intravascular or intraperitoneal injection of histamine or of the histamine releaser, '48/80', into the pseudopregnant rat produced a decidual cell reaction (DCR) in rat uteri with which there was no physical or surgical contact. The data add evidence to the role of histamine in the induction of the DCR.

The histamine-releasing activity of an antihistamine (pyrathiazine) was also used to induce the DCR systemically.

Body weight changes in the mouse during the oestrous cycle and pseudopregnancy

Apart from a tendency to a slight increase in weight at oestrus, no marked cyclic alterations in body weight are evident in the mouse during the oestrous cycle. In pseudopregnancy, however, a definite weight increase (on average 7%) occurs; this weight gain is rapidly lost after removal of the ovaries, but may be maintained after spaying by the administration of progesterone, thus indicating a close similarity to the weight change of pregnancy.