Stabilisation of plasma substrate concentrations: A model for conducting metabolic studies.

Metabolic studies involving changes in plasma substrate concentrations are frequently carried out after an overnight fast. This condition, however, is a transition between the post-prandial period and the beginning of starvation, and thus is associated with rapid changes in the plasma concentration of many substrates. Such alterations might interfere with the interpretation of modifications in plasma concentrations resulting from experimental manipulations. Infusion of glucose at a rate of 250 mg kg(-1) h(-1) for 1h and subsequently at 162 mg kg(-1) h(-1) together with amino-acids at 50 mg kg(-1) h(-1) is used to stabilise the plasma concentration of most substrates within 3 h, a condition which is maintained for the subsequent 5 h or more. This study offers a model which is more suitable for many metabolic investigations than overnight fasting and which takes little time or expense to prepare.