Estrogen-induced changes in high-energy phosphate metabolism in rat uterus: 31P NMR studies

Changes in the concentrations of high-energy phosphate metabolites were measured by 31P NMR spectroscopy of surviving rat uteri from 0-48 h following estrogen administration. Concentrations (millimoles per kilogram wet weight) of these metabolites in the untreated immature uterus, measured at 4 degrees C, were found to be the following: creatine phosphate (CP), 2.1 +/- 0.2; nucleoside triphosphates, mainly adenosine 5'-triphosphate (ATP), 4.6 +/- 0.4; phospho monoesters, primarily sugar phosphates (SP), 5.4 +/- 0.7; and inorganic phosphate (Pi), 0.8 +/- 0.4. Adenosine 5'-diphosphate (ADP) concentration was estimated to be approximately 40 mumol/kg wet weight from the assumed equilibrium of the creatine kinase reaction. The concentration of CP, and to lesser extent ATP and SP, declined within the first 1.5-3 h after injection of 17 beta-estradiol, returned to control values between 6 and 12 h, and then increased, reaching maximal concentrations at 24 h. From the fractions of the total soluble ATP in free and Mg2+-bound forms, [free Mg2+] in the untreated uterus was estimated to be 0.2-0.4 mmol/kg wet weight. An increase in [free Mg2+] in the uterus was detected 1.5 h after estrogen injection. A subsequent parallel increase in the ratio of ATP to CP concentrations suggests that estrogen can also affect the apparent creatine kinase equilibrium by modulating [free Mg2+].