Maternal nutrition and stage of early pregnancy in beef heifers: Impacts on expression of glucose, fructose, and cationic amino acid transporters in utero-placental tissues 1

We hypothesized that maternal nutrition and day of gestation would impact utero-placental mRNA expression of the nutrient transporters GLUT1, GLUT5, CAT-1, CAT-2, and CAT-3 in beef heifers. Crossbred Angus heifers (n = 49) were estrous synchronized, bred via AI, assigned to nutritional treatment (CON = 100% of NRC requirements for 0.45 kg/d gain and RES = 60% of CON) and ovariohysterectomized on d 16, 34, or 50 of gestation (n = 6 to 9/d); Non-bred, non-pregnant (NB-NP) controls were fed the CON diet, not bred, and were ovariohysterectomized on d 16 of the synchronized estrous cycle (n = 6). The resulting arrangement of treatments was a 2 × 3 factorial + 1 (CON vs. RES × d 16, 34, or 50 + NB-NP controls). Caruncle (CAR), intercaruncular endometrium (ICAR), and fetal membranes (FM [chorioallantois]), were obtained from the pregnant uterine horn (the uterine horn containing the conceptus) immediately after ovariohysterectomy. On d 50 cotyledons (COT), intercotyledonary placenta (ICOT) and amnion (AMN) were also collected. Relative expression of nutrient transporters was determined for each tissue utilizing NB-NP-CAR and NB-NP-ICAR tissues as the baseline. For FM, NB-NP endometrium served as the baseline. There was no interaction of day × treatment (P ≥ 0.20) for any genes in CAR. However, CAR expression of GLUT1 was greater (P < 0.01) on d 16 compared with d 34 and 50, and GLUT5, CAT-1, and CAT-2 were greater (P ≤ 0.05) on d 34 compared with d 16 and 50. In ICAR, CAT-2 was the only gene to be influenced by the day × treatment interaction (P = 0.01), being greater in d 50 CON compared with d 34 CON and d 16 and 50 RES. In ICAR, expression of GLUT1 was greater (P < 0.01) on d 16 compared with d 34, and expression of CAT-1 was greater (P < 0.01) on d 34 and 50 compared with d 16. In FM, expression of GLUT5 was greater (P = 0.04) on d 16 compared with d 50 of gestation, and expression of CAT-1 was greater (P < 0.01) on d 34 and 50 compared with d 16. On d 50, expression of GLUT1, CAT-1, and CAT-3 expression were all greater (P < 0.05) in AMN compared with COT and ICOT, and expression of GLUT5 was greater (P < 0.01) in ICOT compared with COT and AMN. These data indicate that day was a more influential factor for mRNA expression of utero-placental glucose and cationic AA transporters than maternal nutritional status in heifers during early pregnancy.