Effects of progesterone on glucose metabolism in isolated acini from mammary glands of lactating rats

Abstract

Isolated acini from lactating rat mammary gland were incubated with glucose (5 m m) and progesterone. The steroid (0.1 m m) decreased glucose utilization and pyruvate accumulation, but increased the formation of lactate. The production of 14CO 2 and 14C-labeled lipid from [1- 14C]glucose, and the incorporation of 3H 2O into lipid were also inhibited by progesterone. At lower concentrations of progesterone (0.01–0.025 m m) the only effects were an increased [lactate], a decreased [pyruvate], and a consequent rise in the lactate/pyruvate ratio. Addition of dichloroacetate, an activator of pyruvate dehydrogenase, did not reverse these effects and assays of active pyruvate dehydrogenase showed no inactivation by progesterone. The steroid did not affect pyruvate utilization but markedly inhibited the removal of lactate, suggesting that progesterone causes a decreased reoxidation of cytosolic NADH and thus alters the cytosolic redox state. The findings are discussed in relation to the physiological role of progesterone during pregnancy and lactation.