Uterine media proteins in the rat during gestation.

Uterine proteins secreted in response to estrogen and modulated by progesterone have previously been demonstrated in the immature rat. An in vitro radiolabeling technique with 35S-methionine was used to culture uteri from animals in estrus, pregnancy and the post partum period. Proteins released into the media (media proteins) were analyzed by sodium dodecyl sulphate-polyacrylamide gel electrophoresis. On Days 1 and 2 of pregnancy, a 115,000 M.W.--protein similar in molecular weight to one previously described by this laboratory--is prominent. Its disappearance by Day 3 coincides with increased progesterone secretion. The appearance of a 43,000 M.W. protein is the most marked change at the time of blastocyst invasion of the uterine epithelium. A new 160,000 M.W. protein begins to emerge on Day 5 and is prominent in later gestation. The latter protein is thought to be a product of the uterine decidua. Its production in ovariectomized animals is increased in the presence of progesterone and a nonspecific decidual stimulus. In the immediate post partum period, a 115,000 M.W. protein reemerges, and the 160,000 M.W. protein disappears. It is believed that these proteins are influenced by the hormonal events of pregnancy and may represent an expression of the genetic control of gestation.