Effect of dietary protein quality and quantity on glucose utilization in rat mammary glands during lactation

Abstract

The effects on glucose metabolism in the mammary gland of feeding diets deficient in protein quality or quantity from conception through day 4 of lactation were measured. Protein sources were 13% casein plus methionine (13CM), 13% wheat gluten (13WG) or 5% casein plus methionine (5CM). Dams were sacrificed on day 20 of gestation or day 4 of lactation. Mammary slices or isolated acini were incubated with 5 mM [U- 14C] glucose in the presence and absence of insulin and recovery of 14C in CO 2, lipid and lactose determined. In slices on day 4 of lactation, neither dietary protein quality or quantity significantly influenced incorporation of labeled glucose into CO 2, lipid or lactose. Insulin significantly increased incorporation into CO 2 and lipid 15% and 17%, respectively, and reduced incorporation into lactose 16%. In acini on day 4 of lactation, reduction in protein quality (13WG vs. 13CM) reduced lipogenesis and lactose synthesis per mg DNA, but no consistent effect of insulin was observed. In both slices and acini, incorporation rates were significantly higher on day 4 of lactation than on day 20 of gestation. The almost total failure of lactation previously observed in 13WG fed dams likely is related at least in part to a reduction in glucose utilization per secretory cell as well as to reductions in mammary gland size and content of DNA, RNA and protein previously observed.