Location of the Estrogen Effect on Uterine Glucose Metabolism. ∗

Summary

Measurements of incorporation of ¹⁴C from differentially labelled glucose and pyruvate into uterine lipid and CO₂ were used to evaluate early metabolic changes produced by estradiol in immature rat uterus. Tissue was incubated with the isotopes in vitro after hormone treatment in vivo. With pyruvate-3-¹⁴C as substrate, substantially more ¹⁴CO₂ is produced than with glucose-1-¹⁴C or glu-cose-6-¹⁴C as substrates. Also, ¹⁴CO₂ output from glucose-1-¹⁴C is about double that from glucose-6-¹⁴C. Estradiol treatment causes a similar increase of ¹⁴C incorporation into lipid with either of the glucose substrates or with pyruvate. This suggests that the estradiol effect on lipid synthesis is beyond pyruvate. A differential effect on ¹⁴CO₂ production from glucose and pyruvate, however, locates an estradiol effect between these substrates. Furthermore, the estradiol acceleration of ¹⁴CO₂ production from glucose-1-¹⁴C and glucose-6-¹⁴C is equal. This suggests that the site of estrogen stimulation of uterine glucose metabolism is prior to the formation of glucose-6-phosphate and therefore implicates the transport step, the phosphorylation step, or both.