Submitted to: Journal of Clinical Endocrinology and Metabolism
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/2/2003
Publication Date: 2/1/2003
Citation: Sunehag AL, Tigas S, Haymond MW, Contribution of Plsama Galactose and Glucose to Milk Lactose Synthesis during Galactose Ingestion. J Clin Endocrinol Metab 88:225-229, 2003. Interpretive Summary: Using an iv infusion of galactose labeled with stable isotopes and oral administration of unlabeled galactose, the present study demonstrated that ingestion of galactose results in direct uptake of galactose by lactating mammary tissue with conversion to both glucose and galactose in lactose. Despite the galactose ingested, the glucose production in this and our previous fasting studies were essentially the same, i.e. the oral galactose did not increase maternal glucose appearance rates. This study combined with previous studies demonstrate that although plasma glucose is the primary source of milk lactose, plasma galactose is a potential substrate for milk lactose during ingestion of galactose.
Technical Abstract: We have previously demonstrated that plasma glucose contributed 80% in the fed and 60% in the fasted state to lactose synthesis in humans, and de novo synthesis in the breast contributing to both the glucose and galactose moieties accounted for the remaining 20% and 40%, respectively, of lactose. The present study was conducted to determine, in lactating women, whether oral galactose is directly incorporated from plasma galactose into glucose and galactose in milk lactose or via conversion of galactose to glucose in the liver. Six healthy exclusively breast-feeding women (30 ± 2 yr) (mean ± SE) ingested galactose at 22 µmol·kg-1·min-1 for 9 h after an overnight fast during infusion of [6,6-2H2]glucose and [1-13C]galactose. We observed that 69 ± 6% of glucose and 54 ± 4% of galactose in lactose were derived directly from plasma glucose, whereas 7 ± 2% and 12 ± 2% of glucose and galactose in lactose, respectively, were derived directly from plasma galactose. De novo synthesis of glucose and galactose via hexoneogenesis accounted for 25 ± 8% and 35 ± 6%, respectively. We conclude that during ingestion of galactose the contribution from plasma glucose to glucose and galactose in lactose was similar to that of a short-term fasting, but part of the de novo synthesis of glucose and galactose in the breast was replaced by direct uptake of galactose.