Metabolic adaptation to experimentally increased glucose demand in ruminants

Four Dorset wethers were studied in a Latin square design with 72-h periods to determine the metabolic adaptations that occur in support of increased glucose demand in ruminants. Wethers injected at 8-h intervals with excipie nt or a total of .5, 1.0, or 2.0 g/d of phlorizin excreted an average of 0, 72.7, 97.9, and 98.5 g/d of glucose into the urine, respectively. Both acu te (2 to 24 h after the first injection) and chronic (8-h intervals from 8 to 72 h after the first injection) adaptations of plasma variables to phlor izin treatment were assessed. Concentrations of plasma glucose decreased li nearly with increasing phlorizin dose during the Ist 24 h of treatment and tended to decrease linearly with phlorizin dose during 8 to 72 h of treatme nt. Urea N tended to increase linearly during 2 to 24 h and increased linea rly during 8 to 72 h. Nonesterified fatty acids increased linearly with phl orizin injection during the entire treatment period. P-Hydroxybutyrate incr eased quadratically with phlorizin injection during 2 to 24 h and tended to increase quadratically during 8 to 72 h. The ratio of insulin to glucagon tended to decrease linearly with phlorizin injection during the Ist 24 h bu t was unaffected from 8 to 72 h. Triiodothyronine, but not thyroxine, tende d to decrease linearly with phlorizin injection during 8 to 72 h. Cortisol was not affected by treatment. Digestibilities of energy and N were not aff ected by treatment. Urinary energy excretion increased with phlorizin injec tion in proportion to the amounts of glucose excreted into the urine. These data indicate that phlorizin-treated wethers largely adapted to phlorizin treatment by 24 h after the first injection and are a suitable model for fu rther investigations of hepatic adaptation to increased glucose demand in r uminants.