Lack of correlation between milk glucose concentrations and rates of milk production in the rat

Concentrations of lactose, alpha-lactalbumin (alpha-la), glucose and glucose-6-phosphate were measured in milk obtained from rats under conditions where the rates of milk production varied from 0 to 2.6 g/h. In the milk from rats fed a low protein diet where milk production was 0.9 g/h, the concentration of alpha-la was 1.5 mg/ml, being significantly lower than that in the milk of control rats at 2.9 mg/ml and where the rate of milk production was 2.6 g/h. No differences were detected in the glucose concentrations. When rats were fed restricted amounts of the control diet and where milk production varied from 0 to 1.7 g/h during the course of the day, no differences in the concentrations of either alpha-la or glucose were detected. These results suggest that considerable caution must be used in interpreting the significance of milk glucose in the rat.