Glucose and Glucose Transporters in Pig Uteri and Conceptuses.

Abstract

Glucose, the main energy source for mammalian embryos during the peri-implantation period, may promote growth and development of conceptuses via the FRAP1 nutrient sensing cell signaling pathway. Therefore, mechanisms for glucose transport into the uterine lumen and uptake by conceptuses are essential. We reported significant increases in glucose in the uterine lumen during early pregnancy in sheep associated with increases in expression of both facilitative and sodium-dependent glucose transporters in the uterine endometrium that were regulated by pregnancy, progesterone (P4) and interferon tau (IFNT). However, little information is available on glucose transporters in uteri and conceptuses in other domestic animals including pigs. Experiment 1 determined effects of day of the estrous cycle and pregnancy on total recoverable glucose in uterine flushings from gilts on Days 5, 9, 12 and 15 of the estrous cycle (Cy) and Days 9, 10, 12, 13, 14 and 15 of pregnancy (Px) (n=4). Total recoverable glucose increased (P<0.05) with day of the Cy and Px. Experiment 2 determined recoverable glucose in uterine flushings of gilts ovariectomized on Day 12 and treated daily with either corn oil (OVX-CO; n=4) or 200 mg progesterone (OVX-P4; n=5) to Day 39 and hysterectomized on Day 40. Recoverable glucose in uterine flushings (mean + SEM; nmol) was greater for OVX-P4 than OVX-CO gilts (4,955+2534 vs 726+133), but this difference was not significant due to variability and the small number of gilts. Experiment 3 determined amounts of glucose in uterine flushings of gilts on Day 90 of pseudopregnancy (PP) that was induced by treatment with 5 mg/day estradiol benzoate on Days 11 to 15 after onset of estrus. The flushings (109+24 ml) contained significant amounts (nmol) of glucose (14,007+3,946). Uterine and conceptus tissues collected from experiments 1-3 were examined by in situ hybridization for expression of Facilitated Glucose Transporters SLC2A1, SLC2A2, SLC2A3 and SLC2A4. Results indicated that: 1) SLC2A3 mRNA was not detectable or very weak in conceptuses and endometria, respectively; 2) SLC2A1 mRNA was expressed by all cell types in conceptuses and was abundant in uterine luminal epithelia (LE) of Cy, Px, PP and OVX-P4 gilts; 3) SLC2A4 mRNA was moderately abundant in LE of Px, but not Cy gilts, only between Days 13 and 25 of Px and LE and GE of OVX-P4 gilts, and not detected in LE or GE of PP gilts; 4) SLC2A2 mRNA was abundant in conceptuses from Days 12 to 40 of pregnancy, decreased to Day 50 and then increased and was maintained specifically in placental areolae and basal crypts of the chorioallantois to Day 80 of gestation. SL2CA2 was also expressed in uterine LE of Px and PP gilts and LE and GE of OVX-P4 gilts. Results of these studies indicate that: 1) the availability of glucose increased in the uterine lumen of Cy and Px gilts between Days 9 to 15; 2) glucose was abundant in uterine flushings from PP and OVX-P4 gilts; 3) temporal and cell specific changes in abundance of mRNAs for specific glucose transporters in uterine LE and GE, as well as chorioallantois likely affect abundance of glucose in the uterus and conceptus; and 4) SLC2A1 expression in uterine endometrium was stimulated by P4. Thus, facilitative glucose transporters responsible for transport of glucose into the uterine lumen of pigs occurs primarily when the uterus is under the influence of progesterone and are available for transport of glucose to the conceptus. (poster)