Abstract
In cattle, conceptus-maternal interactions are critical for the establishment and maintenance of pregnancy. A major component of this early interaction involves the transport of nutrients and secretion of key molecules by uterine epithelial cells to help support conceptus development during the peri-implantation period of pregnancy. Objectives were to: 1) analyze temporal changes in the amino acid (AA) content of uterine luminal fluid (ULF) during the bovine estrous cycle; 2) understand conceptus-induced alterations in AA content; 3) determine expression of AA transporters in the endometrium and conceptus; and 4) determine how these transporters are modulated by (Progesterone) P4. Concentrations of aspartic acid, arginine, glutamine, histidine, lysine, isoleucine, leucine, phenylalanine and tyrosine decreased on Day 16 of the estrous cycle but increased on Day 19 in pregnant heifers (P<0.05). Glutamic acid only increased in pregnant heifers on Day 19 (P<0.001). Asparagine concentrations were greater in ULF of cyclic compared to pregnant heifers on Day 7 (P<0.05) while valine concentrations were higher in pregnant heifers on Day 16 (P<0.05). Temporal changes in expression of the cationic AA transporters SLC7A1 SLC7A4 and SLC7A6 occurred in the endometrium during the estrous cycle/early pregnancy coordinate with changes in conceptus expression of SLC7A4, SLC7A2 and SLC7A1 (P<0.05). Only one acidic AA transporter (SLC1A5) increased in the endometrium while conceptus expression of SLC1A4 increased (P<0.05). The neutral AA transporters SLC38A2 and SLC7A5 increased in the endometrium in a temporal manner while conceptus expression of SLC38A7, SLC43A2, SLC38A11 and SLC7A8 also increased (P<0.05). P4 modified the expression of SLC1A1, -1A4, -1A5, -38A2, -38A4, -38A7, -43A2, -6A14, -7A1, -7A5 and -7A7 in the endometrium. Results demonstrate that temporal changes in AA in the ULF reflect changes in transporter expression in the endometrium and conceptus during early pregnancy in cattle, some of which are modified by P4.
Highlights
A major cause of infertility in cattle is embryo mortality due to conceptus and/or uterine dysfunction during the pre-implantation period of pregnancy
The basic amino acids arginine, histidine and lysine, displayed similar changes in abundance as the concentration of all these amino acids decreased on Day 16 of the estrous cycle compared to other days of the estrous cycle
This decrease did not occur in pregnant heifers; the concentrations of all three basic amino acids in uterine luminal fluid (ULF) was greater on Day 19 compared to Day 16 (P,0.05)
Summary
A major cause of infertility in cattle is embryo mortality due to conceptus and/or uterine dysfunction during the pre-implantation period of pregnancy. Conceptus-maternal interactions are critical to the establishment and maintenance of pregnancy Major components of this early conceptus-maternal interaction involve transporters for nutrients and secretions of key molecules by uterine epithelial cells that support conceptus development during the peri-implantation period of pregnancy [4,5,6,7]. These secretions and transported molecules make up histotroph that represents maternal contributions to uterine luminal fluid (ULF). The expression of cationic [16], acidic and neutral amino acid transporters is altered in a spatial and temporal manner in both the endometrium and conceptus of sheep during early pregnancy [13] and is modulated by ovarian progesterone (P4) and/or conceptus interferon tau (IFNT), prostaglandins and cortisol in vivo [17,18,19]
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