Fuel oxidation by insulin-dependent diabetics during late pregnancy in response to an oral glucose load.

1. To determine the oxidative response to a 50-g oral glucose challenge by diabetic women during late pregnancy under a more intensive therapeutic regimen than is conventionally employed, six normal pregnant women and ten insulin-dependent pregnant diabetic women were studied during the third trimester. Fuel (carbohydrate and lipid) oxidation rates were determined by indirect calorimetry, blood levels of substrates and C-peptide were measured directly, and glucose metabolism data (oxidation and nonoxidative metabolism) were estimated for both groups at the postabsorptive state and for the 2-h period following glucose ingestion. 2. The increases in the non-protein respiratory quotient (npRQ) and carbohydrate oxidation rates in response to glucose ingestion in the diabetic pregnant group were significantly smaller than in the normal pregnant individuals. The total amount of glucose oxidized by the diabetic pregnant group during the 2-h tests (6.1 +/- 0.6 g/m2) was significantly smaller than the oxidized by the normal pregnant group (8.3 +/- 0.4 g/m2), whereas there was more but not statistically significant lipid oxidation in the diabetic group (3.0 +/- 0.3 vs 2.6 +/- 0.1 g/m2). 3. The diabetic pregnant group not only oxidized less glucose (10.9 +/- 1.1 vs 14.1 +/- 0.8 g, P < 0.05) but more of this hexose remained in their glucose space (9.1 +/- 1.6 vs 3.2 +/- 1.1, P < 0.05) and they excreted 2.8 +/- 1.0 g into the urine. 4. The diabetic pregnant subjects had significantly lower blood levels of lactate, pyruvate and C-peptide than the normal pregnant subjects, but significantly higher blood levels of glucose, beta-hydroxybutyrate and acetoacetate. 5. The present data show that an intensive conventional therapeutic regimen during late pregnancy was not sufficient to completely normalize the glucose-processing capability of insulin-dependent diabetic patients.