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Glucose Redistribution in Lactating Cows Given Dexamethasone¹

Section of Nutrition, Department of Clinical Studies, School of Veterinary Medicine, University of Pennsylvania, Kennett Square 19348

ABSTRACT

Tracer doses of glucose uniformly labeled carbon 14 were given to three lactating cows before and after dexamethasone administration. A series of blood samples was collected for 6 h for radiochemical assay of glucose. Plasma glucose concentration rose from a mean of 61 mg/l00ml to 107 mg/l00ml. The tracer data were analyzed in terms of a three-compartment model. Compartments 1 and 2 represent the glucose pool while compartment 3 acts to partition the total glucose transport through the pool into net glucose transport (irreversible disposal) and recycling. Mean total glucose transport rates were .90 and .91 g/min before and after dexamethasone. Corresponding recycling flows were .13 and .21 g/min. There were significant changes in rate constants representing flows between compartments 1 and 2; rate from 2 to 1 was decreased, while rate from 1 to 2 was increased. These were associated with an increase in the mean mass of compartment 1 from 31 to 61 g. The plasma equivalent space of compartment 1 averaged 13 and 14% before and after dexamethasone; this suggests that compartment 1 represents plasma glucose together with approximately the same amount of extravascular glucose. Thus, changes in rates between 1 and 2 suggest that dexamethasone influences glucose transport across some cell membranes and, perhaps, capillary walls. These kinetic studies indicate that the hyperglycemic effect of dexamethasone in lactating cows is attributable to redistribution of glucose rather than an altered overall production or utilization.

¹ These studies were supported in part by the USPHS (NIH grant AM04927).