Plasma Glucose Kinetics Research Articles

Responses to postruminal infusions of glucose and casein in lactating goats.

1. A study was made in goats of the response in terms of milk production, nitrogen utilization, plasma amino acids and glucose kinetics to postruminal infusions of glucose and casein. Goats in mid-lactation, housed in metabolism cages, were fed on 2 kg basal ration (containing 112 g crude protein (N × 6.25)/kg)/d alone (control) and with daily infusions into the abomasum of 45 g casein or 45 g glucose.2. Milk production increased with casein infusion (P < 0.01), but not with glucose infusion, being 1.59, 1.86 and 1.62 kg/d with the control, casein and glucose infusions respectively. Milk composition was unaffected except for milk fat, which was decreased by the glucose infusion.3. The goats were in positive N balance on the basal ration. Milk N output increased with casein infusion, by an amount equivalent to 27% of the infused N.4. The concentration of dispensable amino acids in arterial plasma was decreased with casein infusion and increased with glucose infusion.5. Glucose kinetic measurements with control, casein and glucose infusions indicated that pool sizes were 247, 279 and 302 mg/kg live weight0.75, and irreversible losses were 5.5, 6.7 and 7.0 mg/kg live weight0.75 per min respectively. The differences between the results obtained from the glucose and casein infusions were not significant (P < 0.05).6. The results of the experiment indicate that the increased milk production obtained when casein was infused was not due to enhanced gluconeogenesis.

Effects of thyroid disease on glucose oxidative metabolism in man. A compartmental model analysis.

Glucose oxidation to CO(2) in man at the fasted, steady state has been investigated in normal, hypothyroid, patients by monitoring the specific activity of plasma glucose and expired CO(2) after intravenous injection of glucose-1-(14)C, glucose-6-(14)C, and sodium bicarbonate-(24)C in tracer amounts. Making certain stoichiometric assumptions about the oxidation of the C-1 and C-6 carbons of glucose to CO(2), the data are incorporated into a multicompartmental model describing the kinetics of plasma glucose, plasma bicarbonate, and the conversion of glucose to CO(2) by the hexose monophosphate pathway and all other series and parallel pathways which oxidize glucose carbon to CO(2) (EMP-TCA). This formulation separates the distribution kinetics of glucose and bicarbonate from the kinetics of glucose oxidation to CO(2). It allows the calculation of a minimal fraction (varphi(t)) of glucose irreversibly oxidized to CO(2) which is based entirely on the duration of the experimental data. This calculation is independent of the extrapolative implications of the model beyond the experimental interval and of the particular model chosen to fit the data. All modeling and data fitting were performed on a digital computer with the SAAM program. Based on a 300 min experiment the analysis suggests that in hypothyroidism there is a decrease in the rate of glucose metabolized irreversibly (rhoG). There is also a decrease in the minimal fraction (varphi(300)) which is completely oxidized to CO(2) by way of the EMP-TCA. rhoG and varphi(300) are 0.56 and 0.42 mmole/min respectively as compared to 0.89 and 0.50 mmole/min respectively in normals. However, the fraction of the C-1 of glucose metabolized irreversibly which undergoes oxidation to CO(2) by the hexose monophosphate pathway (Psi) is not different from normal (0.07 and 0.07 respectively). The hyperthyroid studies suggest that rhoG and varphi(300) are within the normal range (1.01 and 0.46 mmoles/min respectively as compared to 0.89 and 0.50 mmole/min respectively in normals). However, Psi is decreased to less than half the normal value (0.03 as compared to 0.07 in normals).