The clearance of carbon-14-fructose, carbon-14-glucose, and carbon-14-sorbitol by calves at birth and 7 days of age.

Prior to birth, the calf is solely dependent on maternal energy sources. Dramatic changes in blood concentrations of carbohydrates, hormones, and enzymes occur, enabling the neonate to achieve homeostasis. Many of these changes are not well understood. This study was to monitor the metabolism and disappearance of labeled carbohydrates in conjunction with endogenous fructose and glucose. Calves were infused intravenously with 100 muCi of [U-14C]D-fructose, -glucose, or -sorbitol within 12 min of birth and at 7 d of age. Close-interval blood and urine samples were collected until 720 min postinfusion. Radiolabel from the three carbohydrates was separated into parent compound fractions of HPLC. Concentrations of cortisol, insulin, glucose, and fructose were determined from blood. Serum cortisol concentration was 3 to 10 times higher in calves at birth than at 7 d of age. Serum insulin concentrations increased postfeeding in newborn and 7-d-old calves. Insulin concentrations were related to plasma glucose. Endogenous plasma fructose was 63 mg/dl (SE = 7) at birth and was undetectable after 14 h. Glucose was 60 mg/dl (SE = 1) and 92 mg/dl (SE = 8) at birth and at 7 d, respectively. Clearance of radiolabel from glucose at birth and for all the carbohydrates at d 7 was similar. Fructose and sorbitol were cleared more slowly at birth. Radiolabel from fructose at birth was converted very slowly to glucose, but this conversion was rapid at d 7. Sorbitol was converted to fructose at birth but changed quickly to glucose at d 7. The 24-h excretion of radiolabel in urine was less than 4% for fructose and glucose at birth and at d 7. The label from sorbitol appeared in urine at birth (32%) and at d 7 (10%). A source of fructose may provide a slowly utilizable energy source until blood glucose concentrations become stable in the newborn calf.