Glucose turnover and oxidation rates in lactating sheep

Abstract

Labeled glucose was infused intravenously into sheep at various stages of lactation and also following lactation. Mean glucose pool sizes (142-165 mg/kg) and their volumes of distribution (25-27% of body wt) were comparable regardless of milk production or of glucose turnover. Glucose turnover rates were nearly 3 times greater during the peak of lactation (0.6 g/hr. per kg3/4) than during nonlactation (0.23 g/hr. per kg3/4). The rate of lactose production during maximal lactation (0.36 g/hr. per kg3/4), if all was synthesized from plasma glucose, could account for the fate of about 60% of the total glucose utilization and for about 80% of the nonoxidized glucose. Part of the increase in glucose turnover during lactation was due to a roughly twofold increase in the grams of glucose oxidized to CO2 and this was accompanied by a similar twofold increase in the total metabolic rate. In all groups of animals, therefore, a roughly similar porportion (8-9%) of the exhaled CO2 was derived from glucose. Comparisons of these results with data previously obtained on pregnant sheep indicate that more glucose must be furnished by the ewe during lactation than during pregnancy.