The effects of the preimplantation blastocyst in vivo and in vitro on protein synthesis and secretion by cultured epithelial cells from sheep endometrium.

Epithelial endometrial cells were isolated on day 13 from nonpregnant (NPr) and pregnant (Pr) ewes and cultured in the presence or absence of conditioned media from 15-day blastocysts (BM) under optimized conditions in the presence of [35S]methionine (S-met). The incorporation of S-met into secreted protein was analyzed, and individual proteins were identified by autoradiography of two-dimensional sodium dodecyl sulfate polyacrylamide gel electrophoresis. Incorporation of S-met into secreted protein was higher (P less than 0.05) for cells from Pr than NPr animals. Secretion by cells from NPr ewes was increased in three of four cases by addition of BM to the culture medium. Autoradiography of two-dimensional sodium dodecyl sulfate polyacrylamide gel electrophoresis showed five secreted proteins [mol wt range 74,000-120,000; isoelectric point (pI) less than 6.5] which were either absent from or present in only small amounts in secretions from cells from NPr animals. The proportion of these proteins was greatly increased in secretions from cells from Pr animals. The presence of BM in cultures from NPr ewes enhanced the secretion of these same proteins, this effect being maintained even after heat treatment of the BM. One of these proteins had previously been shown to be maximally induced by the presence of estrogen and progesterone. Three other similarly controlled proteins were also enhanced, though to a lesser extent, by the presence of a blastocyst in vivo but were not stimulated by BM in vitro. It is concluded that endometrial epithelial cells from Pr ewes are metabolically more active than those from ewes on day 13, and the blastocyst and its secretions induce the secretion of several specific proteins by epithelial cells, some of these proteins being the same as those controlled by the combination of estrogen and progesterone.