Hexose transport in preimplantation rabbit blastocysts

Self Cite

Summary. The metabolism of glucose in the intact post coitum (p.c.) rabbit blastocyst and in the separated trophectoderm and inner cell mass (ICM) of the Day-7 p.c. embryo was investigated. At Day-6 p.c., glucose traversed the trophectoderm with a half-time of 39 \ m=+-\9\m=.\3 min, and was metabolized to CO2 at a rate of 25\m=.\5\m=+-\1\m=.\6 nmol \ m=. \ cm\ m=-\ 2\ m=. \ h\ m=-\ 1. Neither the Na+ ionophore, amphotericin B, nor cyclic AMP had an effect on glucose metabolism to CO2. Lactate production by the Day-6 blastocyst was largely independent of glucose. At Day-7 p.c. in the intact embryo, CO2 production from glucose significantly decreased to 7\m=.\76\ m=+-\ 2\m=.\8nmol\m=.\cm\m=-\2\m=.\h\m=-\1. Per unit surface area, the metabolism of glucose to CO2 was similar in the separated Day-7 p.c. trophectoderm and ICM. We conclude that the rabbit blastocyst is not highly dependent on glucose, and that the ICM does not utilize glucose as a metabolite to a greater extent than does the trophectoderm, at least in the Day-7 p.c. embryo.

Section: Methodsmentioning

confidence: 99%

“…Individual Day-6 and -7 p.c. embryos were measured as previously described (Robinson et al, 1990) 10pCi/ml. The experiment was terminated by adding 1 H2S04 at a volume twice that of the incubation solution through the diaphragm with a syringe, and then adding 0-5 ml 2-5 N-NaOH to the empty test tube.…”

Section: Methodsmentioning

confidence: 99%

Glucose metabolism in the trophectoderm and inner cell mass of the rabbit embryo

Robinson¹,

Benos²

1991

Self Cite

“…One of the first transporters to be characterized in preimplantation embryos was GLUT1. GLUT1 mRNA is expressed throughout preimplantation development, namely from the 1-cell through the blastocyst stage in the mouse (Hogan et al 1991, Aghayan et al 1992, Morita et al 1992, rabbit (Robinson et al 1990), cow (Lequarre et al 1997, Wrenzycki et al 1998, Navarrete Santos et al 2000, Augustin et al 2001) and human (Dan-Goor et al 1997). Interestingly, GLUT1 was shown by immunofluorescent confocal microscopy to be expressed in the pronuclei of oocytes and in the nucleus of cleavage stage embryos (Pantaleon et al 2001).…”

Section: Introductionmentioning

confidence: 99%

Glucose utilization and the PI3-K pathway: mechanisms for cell survival in preimplantation embryos

Riley¹,

Moley²

2006

The maintenance of optimal glucose utilization during the preimplantation period is critical for embryo survival. A decrease in glucose transport during preimplantation development has been linked to the early steps of programmed cell death in these embryos. Decreased glucose transport is not thought to be simply a consequence of cell death, rather it is thought to be a trigger that can initiate the apoptotic cascade. Extensive apoptosis during the preimplantation period may manifest later in pregnancy as a malformation -or miscarriage, if cell loss is excessive. Phosphatidylinositol 3-kinase (PI3-K) is a known regulator of a number of physiologic responses including cellular proliferation, growth, and survival as well as glucose metabolism. Studies performed in other cell systems have demonstrated that the PI3-K pathway plays a critical role in maintaining glucose transport and metabolism. This review will present the current evidence that suggests that PI3-K is vital for preimplantation embryo survival and development. In addition, data demonstrating that PI3-K activity is important for glucose metabolism during this early developmental period will be discussed.

“…This specific constellation and its physiological implications may have led to the more complex furnishing with glucose transporters in embryos than in differentiated muscle, fat or neuronal cells. Considering glucose uptake by preimplantation embryos, which is in a pmol per embryo per hour range (rabbit: Robinson et al 1990, rat: Brison & Leese 1994, mouse: Martin & Leese 1999, bovine: Donnay & Leese 1999, and assuming a Figure 5 Relative amounts of GLUT1, GLUT3, GLUT4 and GLUT8 mRNA in the trophoblast and embryoblast of rabbit blastocysts. (A) The relative amounts of GLUT1, 3, 4 and 8 transcripts were quantified by semiquantitative RT-PCR in isolated trophoblast (Tr) and embryoblast (Em) of 11 day-6 (d6) blastocysts (1-11) as described in Materials and Methods.…”

Section: Discussionmentioning

confidence: 99%

“…The expression pattern of glucose transporters in preimplantation embryos has been studied in the mouse (Hogan et al 1991, Aghayan et al 1992, Morita et al 1992, Chi et al 1993, Pantaleon et al 1997, rabbit (Robinson et al 1990), bovine (Lequarre et al 1997, Wrenzycki et al 1998, 2003, Navarrete Santos et al 2000, Augustin et al 2001 and human (Dan-Goor et al 1997). In mice, GLUT1 was found in all preimplantation stages.…”

Section: Introductionmentioning

confidence: 99%

Two insulin-responsive glucose transporter isoforms and the insulin receptor are developmentally expressed in rabbit preimplantation embryos

Santos¹,

Tonack²,

Kirstein³

et al. 2004

Glucose is the most important energy substrate for mammalian blastocysts. Its uptake is mediated by glucose transporters (GLUT). In muscle and adipocyte cells insulin stimulates glucose uptake by activation of the insulin receptor (IR) pathway and translocation of GLUT4. GLUT4 is expressed in bovine preimplantation embryos. A new insulin-responsive isoform, GLUT8, was recently described in mouse blastocysts. Thus, potentially, two insulin-responsive isoforms are expressed in early embryos. The mechanism of insulin action on embryonic cells, however, is still not clear. In the present study expression of IR, GLUT1, 2, 3, 4, 5 and 8 was studied in rabbit preimplantation embryos using RT-PCR, Western blotting and immunohistochemistry. The rabbit mRNA sequences for the complete coding region of IR, GLUT4 and a partial GLUT8 sequence were determined by RACE-PCR and sequencing. GLUT4 was expressed in 3-day-old morulae and in 4-and 6-day-old blastocysts. IR and GLUT8 transcripts were detectable only in blastocysts. Blastocysts also expressed GLUT1 and 3, but not GLUT2 and 5. Transcript numbers of GLUT4 and 8 were higher in trophoblast than in embryoblast cells. Translation of IR, GLUT4 and 8 proteins in blastocysts was confirmed by Western blotting. GLUT4 was localized mainly in the membrane and in the perinuclear region in trophoblast cells while in embryoblast cells its localization was predominantly in the perinuclear cytoplasm. The possible function(s) of two insulin-responsive isoforms, GLUT4 and GLUT8, in rabbit preimplantation embryos needs further investigation. It may not necessarily be linked to insulin-stimulated glucose transport.