Creatine metabolism at the uterine-conceptus interface during early gestation in sheep

Ruminant conceptuses that elongate and attach to the uterine luminal epithelium (LE) to establish pregnancy require a large amount of adenosine triphosphate (ATP). The creatine (Cr)-creatine kinase (CK)-phosphocreatine (PCr) system re-generates ATP in dividing and migrating cells such as the conceptus trophectoderm cells. However, little is known about metabolism of Cr within uterine and conceptus tissues in livestock species during early gestation. In this study, Suffolk ewes were ovariohysterectomized on Days 9, 12, 15, 16, 17, 18, 20, or 21 of pregnancy (n = 2-5 animals/per day) to investigate metabolites, mRNAs, and proteins of the Cr-CK-PCr system at uterine-conceptus interface. Amounts of Cr and guanidinoacetate (GA) in uterine flushings increased between Days 12 and 17 of pregnancy. Endometrial expression of mRNAs for GA formation (AGAT), Cr synthesis (GAMT), and Cr/PCr utilization (CKB) was greater on Days 17 and 21 than on Days 9 and 12 of pregnancy. Immunoreactive AGAT was detected in uteri only on Day 21 but not in uteri or conceptuses at earlier days of pregnancy. GAMT, SLC6A8, and CKs were expressed in uterine luminal and glandular epithelia. Immunoreactive CKs (CKB, CKM, and CKMT1) appeared greater on Day 9 than Day 17 of pregnancy. Immunoreactive GAMT and CKs appeared greater in trophectoderm of conceptuses on Day 20 than on Day 15 of pregnancy, whereas the opposite was observed for that of SLC6A8. This study provides insights into cell-, tissue-, and time-specific metabolism of Cr at the uterine-conceptus interface suggesting a role for the Cr-CK-PCr system in ovine conceptus development and implantation.