Select nutrients and glucose transporters in pig uteri and conceptuses.

Abstract

Glucose present in the intrauterine environment can be metabolized, activate cell signaling pathways or be converted to a "storage" form. Total recoverable glucose in uterine fluid of pregnant, but not cyclic pigs increases from Day 12 after onset of estrus in concert with conceptus elongation (Bazer et al. 1991). Transport of glucose into the ovine uterus and its uptake by conceptuses involves sodium-dependent and facilitative glucose transporters (Gao et al. 2009). Glucose can activate FRAP1/mTOR "nutrient sensing" pathway in which protein kinases activate p70S6 through phosphorylation to increase translation of 5'TOP mRNAs (terminal oligopyrimidine tract) (Wen et a/. 2005). Activated FRAP1 also regulates differentiation of trophectoderm (Tr) via Ras transformation by phosphorylating eukaryotic initiation factor 4E binding protein 1 (eIF4EBP1), a translational repressor of CAP-dependent translation (De Benedetti & Rhoads 1990). Select nutrients that stimulate FRAP1 activity in Tr include glucose, arginine (Arg), leucine (Leu) and glutamine (Gln) which may increase expression of IGF2, ODC and NOS mRNAs (Nielsen et al. 1995; Kimball et al. 1999; Martin & Sutherland 2001) which are required for conceptus development, differentiation and implantation through effects on production of NO (Kaliman et al. 1999) and polyamines (Van Winkle & Campione 1983). FRAP1 null mice die shortly after implantation due to impaired cell proliferation and hypertrophy in both the embryonic disc and Tr (Murakami et al. 2004). There are 14 isoforms of facilitative glucose transporters and 6 sodium-dependent glucose transporters. Of these, SLC2A I, SLCSA1 and SLCSA1 I mRNAs are most abundant in endometria and SLC2A3 is uniquely expressed by ovine conceptus Tr and endoderm (Gao et al. 2009). The objective of this study with sexually mature giks was to identify effects of pregnancy, long-term treatment of ovariectomized gilts with progesterone (P4) and estradiol-induced pseudopregnancy (PP) on changes in amounts of select nutrients (glucose, Arg, Leu and Gln) in uterine fluid and expression of glucose transporters in endometria and conceptuses. Experiment 1 determined effects of day of the estrous cycle and pregnancy on total recoverable glucose, Arg, Leu and Gln 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). Total recoverable glucose, Arg, Leu and Gln increased (P< 0.05) with day in Cy and Px gilts, but only Arg increased more in Px than Cy ewes (day x pregnancy status; P<0.05) between Days 12 and 15. Experiment 2 determined recoverable amounts of selected nutrients 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. Values (mean +SEM; nmol) were greater for OVX-P4 than OVX-CO gilts for glucose (4,955+2,534 vs 726+ 133), Arg (207,112 + 160,979 vs 7,409+ 2,877) and Leu (248,255 + 178,599 vs 13,983+ 5,225), but differences were not significant due to high variability and small sample size. Experiment 3 determined amounts of selected nutrients in uterine flushings of gilts on Day 90 of pseudopregnancy (PP) induced by treatment with 5 mg/day estradiol benzoate on Days