Effects of guinea-pig endometrial proteins on phospholipase A2 activity and prostaglandin synthesis.

The major protein secreted by Day-15 guinea-pig endometrium cultured for 24 h had a molecular weight of 68.3 kDa on SDS-PAGE. This protein had no effects on phospholipase (PL) A2 activity in vitro and prostaglandin (PG) production by Day-7 guinea-pig endometrium in culture. Following purification, proteins present in fractions F1, F2, F7, F7:2 and F7:3 (which comprised < 15% of the total amount protein secreted) increased PLA2 activity in vitro. The major proteins in F7:2 had molecular weights of 13.9 and 15.6 kDa on SDS-PAGE, but they had no effect on endometrial PG synthesis in the concentration used (20 mg/ml). Unpurified endometrial secreted proteins had no effect on PLA2 activity, but stimulated endometrial PG synthesis. This stimulation was lost following purification of the proteins, and may have been due to a large amount of contaminating serum albumin. The mechanism by which oestradiol acting on a progesterone-primed guinea-pig uterus stimulates endometrial PGF2 alpha synthesis by a process which is dependent upon increased endometrial protein synthesis still remains obscure.