| Summary: | Northern elephant seal (Mirounga angustirostris) pups maintain a paradoxical fasting hyperglycemia while fasting for 6–8 weeks after nursing ~30 days. The hyperglycemia results from low rates of glucose utilization (due to low insulin) and high rates of glucose carbon recycling. Fatty acids are the major energy substrate during this time, with high rates of palmitate turnover and low ketone levels, as well as nitrogen conservation and low urea turnover. First order rate constants for the model were taken from the literature and entered into a ten compartment matrix model of metabolite flux. Eigenvalues and eigenvectors of the matrix were determined. The initial conceptualization, where carbon atoms left the model, yielded nonzero negative eigenvalues, indicating an open, stable system. Inclusion of a sink which accumulated carbon atoms yielded the same set of negative eigenvalues, and a zero eigenvalue, indicating that this system was closed and stable. The trace (β) of the matrix was a negative real number in both cases, while the determinant () of the matrix was a negative real number in the first case (no sink), and zero in the second case (sink), indicating that the system lies near a stable saddle point in the dimensionless β- phase-plane. The predicted stability of the model system is difficult to reconcile with the biological reality of a fasting animal that cannot survive forever without nutrient inputs.
|
|---|