The effects of maternal nutrient restriction and day of early pregnancy on the location and abundance of neutral amino acid transporters in beef heifer utero-placental tissues.

We hypothesized that maternal nutrition and day of gestation would influence the abundance of the neutral amino acid transporters SLC1A1, SLC1A5, SLC7A5, SLC38A2, and SLC38A7 in heifer utero-placental tissues. Angus-cross heifers (n = 43) were estrus synchronized and bred via AI. At breeding, heifers were assigned to one of two dietary intake groups (CON = 100% of requirements to achieve 0.45 kg/d gain or RES = 60% of CON intake) and ovariohysterectomized on d 16, 34, or 50 of gestation (n = 6 to 9/d). Thus, the experimental design was a completely randomized design with a 2 × 3 factorial arrangement of treatments. Uterine cross sections were taken from the horn ipsilateral to the CL, fixed in 10% NBF, sectioned at 5 µm, and stained for transporters. For each image, the areas of fetal membrane (FM; chorioallantois), endometrium (ENDO), superficial glands (SG), deep glands (DG), and myometrium (MYO) were analyzed separately for relative intensity of fluorescence as an indicator of transporter abundance. Analysis of FM was only conducted on d 34 and 50. In ENDO, SLC7A5 was greater (P < 0.01) in CON compared with RES heifers. In SG, SLC1A1 was greater (P = 0.02) in d 16 RES compared with d 16 CON and d 34 and 50 RES. In DG, SLC1A1 was greater (P = 0.02) on d 16 compared with 50 of gestation. In MYO, SLC1A1 was greater (P = 0.02) in d 50 CON compared with d 16 CON and d 50 RES. Additionally, in MYO SLC38A2 was greater (P = 0.02) in d 16 RES compared with d 16 CON and d 34 RES. In FM, SLC7A5 tended (P = 0.08) to be greater in CON vs. RES. Analysis of all uterine tissues on d 16 determined that expression of SLC1A1, SLC1A5, SL38A2, and SL38A7 differed across uterine tissue type (P < 0.01); however, only SLC7A5 tended (P = 0.10) to differ and be greater in CON compared with RES heifers. Analysis of all utero-placental tissues on d 34 and 50 determined that SLC1A1, SLC7A5, SLC38A2, and SLC38A7 were greater (P ≤ 0.03) in CON compared with RES heifers. Furthermore, abundance of all transporters investigated on days 34 and 50 differed across utero-placental tissue types (P < 0.01). These data support our hypothesis that maternal nutrition and day of gestation influence the abundance of neutral amino acid transporters in utero-placental tissues from days 16 to 50 of gestation. Additionally, these data combined with previously published works help to further elucidate nutrient supply and demands of the maternal and fetal system during early gestation in beef heifers.

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