Relationships between Glucose and Mannose during Late Gestation in Normal Pregnancy and Pregnancy Complicated by Diabetes Mellitus: Concurrent Concentrations in Maternal Plasma and Amniotic Fluid†

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Abstract
Enzymatic assays were modified to permit sensitive and highly reproducible simultaneous measurements of Dmannose and D-glucose in biological fluids during weeks 34–40 of human pregnancy. Plasma mannose and glucose averaged 9.8 ± 0.4 (±SEM) and 790 ± 16 ¼g/ml, respectively, after an overnight fast in pregnant women (n = 22) with normal carbohydrate metabolism. Significantly higherplasma mannose levels were found, despite only minor increases in plasma glucose,in pregnant women with relatively well controlled diabetes mellitus after an overnight fast (16.9 ± 0.6 ¼g/ml mannose; 883 ± 29 ¼gl ml glucose; n = 31) or 3-4 h after breakfast (15.7 ± 1.2 ¼g/val mannose; 1159 ± 101 ¼g/ml glucose; n = 19). Plasma mannose correlated significantly withplasma glucose in the women with diabetes mellitus, particularly after an overnight fast. Samples of amniotic fluid were also obtained from the gravida with diabetes mellitus to provide some index of simultaneous relationships in utero. Amniotic fluid mannose and glucose averaged 5.9 ± 0.4 and 302 ± 24 ¼g/ml, respectively, after an overnight fast and 6.7 ± 1.3 and 459 ± 84 ¼g/ml 3-4 h after breakfast. In amniotic fluid, as in plasma, the concurrent levels of mannose and glucose conformed to relatively fixed relationships. Thus, othfetus and mother appear to be exposed to readily demonstrable amounts of mannose during late gestation and the absolute as well as relative abundance of mannose may be increased coincident with faulty maternal glucoregulation. However, since mannose did not exceed 3% of the concurrent concentration of glucose in any instance, it does not seem likely that endogenous levels of circulating mannose can modify glucose utilization appreciably by competing with glucose for phosphorylatio via hexokinase and subsequent intracellular processing.