CATECHOLESTROGENS AND PROLACTIN IN REGULATING UTERINE GLYCOGEN METABOLISM, MINK

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This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Uterine glycogen (GLY) reserves are a potential source of energy for embryo survival, development, and implantation. Synthesis of GLY is stimulated by estradiol-17¿ (E2) in a reproductive cycle-dependent pattern, being highest during the uterine secretory phase in human's and between proestrous and estrous in rodents. Mink, are seasonal breeder's, that exhibit obligate embryonic diapause resulting in delayed implantation where, depending on the date of breeding, blastocysts may be 60 days old at implantation. Uterine GLY accumulation and mobilization to glucose may be requisite to blastocyst survival, activation (ie: termination of diapause), and implantation in this species. Plasma E2 levels in mink peak on the day of mating-induced ovulation, and again near the time of implantation. In addition, the uterus metabolizes E2 to catecholestrogens (CE) such as 2-hydroxyestradiol (2-OHE2) and 4-hydroxyestradiol (4-OHE2). Previously, we have shown that E2 and CEs increase uterine GLY concentrations 6-fold in ovariectomized (OVX) mink. These hormones simultaneously reduced the expression of uterine Glycogen Synthase Kinase-3¿ (GSK-3¿), an enzyme that phosphorylates and inactivates Glycogen Synthase (GS). Because GS is rate limiting in GLY synthesis, the reduction in GSK-3¿ expression, should remove inhibition on GS resulting in increased GLY production. Both E2 and 4-OHE2 promote the phosphorylation and inactivation of GSK-3¿, further enhancing GLY synthesis. Also, 4-OHE2 and 2-OHE2 increased uterine GS expression while reducing expression of the GLY catabolizing enzyme GLY-Phosphorylase (GP), which also increases uterine GLY accumulation. Because of their very short half-live's, the effects of CE's are localized and not detectable in the blood. In addition to E2, prolactin (PRL) is essential to implantation in mink through its luteotropic actions increasing progesterone (P4) levels in the circulation. Moreover, PRL receptors have been identified in the mink uterus, suggesting that direct uterotropic actions by the hormone may also promote blastocyst implantation. We hypothesize that PRL increases GLY catabolism, providing glucose for blastocyst activation, implantation, and contribute to increased litter sizes. We will test this hypothesis in three specific aims designed to determine (1) the effects of E2, 4-OHE2, and 2-OHE2 on the phosphorylation of GS and GP; (2) if 4-OHE2 & 2-OHE2 act on the uterus through pathways independent from E2; and (3) if PRL has glycogenolytic actions in the mink uterus. Immunoblots will be used in specific aim 1. For Aim 2, mink will be treated with the estrogen receptor antagonist ICN -182,780, alone and in combination with E2, 4-OHE2, or 2-OHE2 and uterine GLY levels will be measured. For Aim 3, mink will be made hyperprolactinemic using the dopaminergic antagonisthaloperidol (HAL) and uterine GLY concentrations measured. Data from these studies will contribute to our understanding of efficient reproduction in mink.