Night-time metabolic changes in normal subjects in the absence of the dawn phenomenon.

Metabolic changes have been followed overnight in 10 normal subjects. Blood glucose and serum C-peptide concentrations were constant from 0100 to 0800 h, as was serum insulin. Plasma NEFA, and blood glycerol and 3-hydroxybutyrate concentrations fell steadily after 0200 h however, suggesting a decreasing rate of lipolysis, fatty acid oxidation, and ketogenesis. The changes in NEFA concentrations were consistent with small rises in blood pyruvate and alanine concentrations. While it is unclear how glucose homeostasis is maintained when major changes are occurring in turnover of other metabolic intermediates, the results suggest potential mechanisms for an overnight disturbance of glucose metabolism in stressed or insulin deficient man.