Glucose and pyruvate metabolism in preimplantation blastocysts from normal and diabetic rats.
Glucose metabolism was analysed in day-5 rat blastocysts incubated in the presence of [5-3H]-, [6-14C]- or [U-14C]glucose. Glycolysis, quantified by 3H2O recovery rate, was the main pathway of glucose utilization by fresh (11.5 +/- 0.36 pmol per embryo h-1) or cultured (24 h) blastocysts (20.4 +/- 0.6 pmol per embryo h-1). Glucose consumption rate was almost saturated at a medium glucose concentration of 0.28 mmol l-1 (Km: 0.17 mmol l-1; Vmax: 23 pmol per embryo h-1). A further 10% increase in glucose utilization was obtained with a tenfold higher glucose concentration (3 mmol l-1). Phloretin completely abolished the rapid component of glucose utilization kinetics, suggesting the existence of a Na(+)-independent glucose transport system. Less than 1% of [6-14C]glucose consumed by cultured blastocysts was oxidized through the Krebs cycle. [1-14C]pyruvate, however, was oxidized at a rate of 2 pmol per embryo h-1 by fresh blastocysts. The pentose-phosphate pathway accounted for about 2% of glucose utilization. One to two per cent of the total glucose metabolized in 24 h was retained in macromolecules. Insulin had no effect on glucose uptake, utilization, incorporation and turnover, or on pyruvate oxidation. Blastocysts from diabetic mothers utilized glucose at a rate similar to that of normal blastocysts. These results show that glucose is actively taken up by rat blastocysts and utilized mainly through the Embden-Meyerhof pathway, which is rapidly saturated at low glucose concentrations. Retention of glucose-derived products in macromolecules, although relatively small, may modulate the effect of high glucose concentrations on embryo growth.(ABSTRACT TRUNCATED AT 250 WORDS)
Dufrasnes
E
E
Physiology of Human Reproduction Research Unit, University of Louvain, School of Medicine, Brussels, Belgium.
Vanderheyden
I
I
Robin
D
D
Delcourt
J
J
Pampfer
S
S
De Hertogh
R
R
D000818:Animals; D001755:Blastocyst / Q000378:metabolism*; D002478:Cells, Cultured; D003921:Diabetes Mellitus, Experimental / Q000378:metabolism*; D005947:Glucose / Q000378:metabolism*; D007328:Insulin / Q000378:metabolism; D011773:Pyruvates / Q000378:metabolism*; D051381:Rats; D017208:Rats, Wistar
D007328:Insulin; D011773:Pyruvates; D005947:Glucose