Average Plasma Glucose Level Research Articles

Contrasting Patterns of Energy Substrates in Tundra and Meadow Voles

The effects of excitement, crowding, 5 C acclimation, and -40 C exposure on liver and muscle glycogen reserves and plasma glucose, urea, and FFA levels of the tundra vole and meadow vole are compared. These two closely related species were selected when the tundra vole failed to exhibit the usual hyperglycemic response when handled; while the meadow vole like the red-backed vole and collared lemming at least triple average plasma glucose levels within 5 min. Crowding of two or three voles, in a small cage, depleted glycogen reserves in the liver and muscle of both the meadow and tundra voles, with the former having a third less plasma glucose and a seventh more plasma urea nitrogen level than the latter. Cold acclimation provides a more striking contrast, for reserves of liver glycogen are nearly lost (95%) in the tundra vole and are retained in the meadow vole, while muscle glycogen of both remain at levels of unacclimated controls. Cold resistance at -40 C appeared similar in both species but related to the retention of liver glycogen levels of the meadow vole and not the tundra vole. Conversely, sensitivity to cold (Tb > 35 C) in the tundra vole resulted in a threefold increase in plasma FFA levels that did not appear in the cold-sensitive meadow vole. Possible explanation for these differences in utilization of reserves are sought in the larger amounts of brown fat found in the tundra vole than in the meadow vole, two sympatric and phylogenetically closely related species.