Glucose transporter expression in rat embryo and uterus during decidualization, implantation, and early postimplantation

Efficient transfer of glucose from the mother to the embryonic compartment is crucial to sustain the survival and normal development of the embryo in utero, because the embryo's production of this primary substrate for oxidat ive metabolism is minimal. In the present study, the temporal sequence of e xpression of the sodium-independent facilitative glucose transporter isofor ms GLUTs 1, 3, 4, and 5 was investigated in the developing rat uteroembryon ic unit between conception and Gestational Day 8 using immunohistochemistry . The GLUTs 1, 3, and 4 were expressed in the embryonic tissues after the s tart of implantation, being colocalized in the parietal endoderm, visceral endoderm, primary ectoderm, extraembryonic ectoderm, and the ectoplacental cone. In the uterus, a faint GLUT1 labeling emerged, but not until Gestatio nal Day 3, in the luminal epithelium, endometrial stroma, and decidual cell s. The intensity of GLUT1 staining increased in the latter population with progressing decidualization. Endometrial glands and myometrial smooth muscl e cells stained neither for GLUT1 nor for GLUT3 until postimplantation. Dur ing all developmental stages examined, GLUT4 was visualized throughout the pregnant rat uterus, as was GLUT3 (with the above-mentioned exceptions). Th e density of GLUT5 was generally less than the sensitivity of the immunohis tochemical detection method in all tissues investigated. In conclusion, the data point to a significant expression of the high-affinity glucose transp orters GLUTs 1, 3, and 4 in the rat uteroembryonic unit, providing supporti ve evidence for an important role of facilitative glucose diffusion during peri-implantation development.