Effects of 17β-Estradiol on High Energy Phosphate Concentrations and the Flux Catalyzed by Creatine Kinase in Immature Rat Uteri:31P Nuclear Magnetic Resonance Studies*

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Abstract
31P nuclear magnetic resonance (NMR) was used to study the effects of 17.beta.-estradiol on the content of phosphates and on the flux catalyzed by creatine kinase in immature rat uteri. Perifusion with oxygenated medium at 36 C maintained the uteri in a viable state for at least 10 h in vitro during 31P NMR measurements. In vitro administration of 17.beta.-estradiol to the perifused uteri induced changes in the concentration of the high energy phosphates similar to those found after in vivo stimulation: a rapid fall in the concentrations of ATP, phosphocreatinine, and the phosphomonoesters during the first 2 h, followed by a slower return to initial concentrations by approximately 6 h. Analysis of the time course of this modulation indicated that after estrogen stimulation, the energy utilization rate was about twice the production rate. The flux through the creatinine kinase (CK) reaction was measured independently using 31P magnetization transfer techniques; it was found to increase in uteri 24 h after estradiol injection by the same extent (65%) as the specific activity of CK measured by a spectrophotometric assay. The congruence between the results of these two techniques (in the absence of increased substrate concentrations) provides evidence that the early stimulation of brain-type CK synthesis by estrogen results in a net increase in the concentration of this enzyme.