Mouse ascites golgi (MAG) mucin expression and regulation by progesterone in the rat uterus

Objective: To study the regulation of the blood group A-related high-molecu lar weight mucin glycoprotein epitope (mouse ascites golgi, MAG)-a menstrua l cycle-dependent marker of endometrial receptivity-in a non-human endometr ium model. Methods: Immature Sprague-Dawley rates were injected with 1 mug of estradio l, 100 mug of testosterone, 100 mug of dexamethasone, 2.5 mg of progesteron e (P), 0.325 mg of RU486, P and RU486, 100 mug of tamoxifen, or vehicle for 3 days, sacrificed, and the uteri were stained for MAG. Immunohistochemist ry and blood analysis were the measurements used to compare the specimens f rom the exogenous hormonal and endogenous hormonal groups. Electron microsc opy was used to locate the MAG epitope in one pseudopregnant adult Sprague- Dawley rat. Results: The MAG epitope was present in endometrial glands of Sprague-Dawle y rats, with maximal expression during proestrus and diestrus. Electron mic roscopy confirmed the Golgi location of this MAG epitope. In the untreated group. less than 0.5% of endometrial glands stained for MAG. The MAG was se en only in the glands of the P-treated rats and RU486 blunted this stimulat ory effect by more than 95 5. As little as 0.1 mg of P promoted MAG express ion, with maximal response at 2.5 mg. Staining was seen 24 hours after P tr eatment, peaked at 72 hours, then declined. Induction of endogenous P by su perovulation with pregnant mare serum gonadotropin (PMSG) and hCG (pseudopr egnancy) also resulted in strong MAG glandular staining. Conclusion: Our results suggest that the MAG epitope is cyclically expresse d and induced by P in rat endometrial glands. (J Soc Gynecol Investig 2001; 8:216-33) Copyright (C) 2001 by the Society of Gynecologic Investigation.