Estimates of the volume of fluid and the concentration of cations in the uterus were made by flushing the uterine cavity of mice mated to vasectomized males and measuring the concentrations of sodium and potassium cations in the recovered fluid. On day 1 following mating, large volumes of fluid (greater than 90 microL) were found in the uterus but, from days 2 to 5, only 2-5 microL of fluid were present. The ratio of sodium to potassium fell from 4.5:1 on day 1 to 1.8:1 on days 2 to 5 of pseudopregnancy, indicating that uterine fluid in the mouse has a high K+ content ranging from 35 mEq L-1 on day 1 to 75 mEq L-1 on day 5. Glucose, lactate and pyruvate in uterine flushings were also assayed and their concentration in uterine fluid calculated using the volumes found above. The level of all substrates was low on day 1 after mating. From day 2 onwards approximately 1 mM glucose was present in the fluids. The concentration of lactate was more variable, and peaked at 4 mM on day 2 of pseudopregnancy. In general, the concentration of pyruvate was 10% of the lactate value.

The incorporation and turnover of glucose carbon by mouse embryos during short periods of in vitro culture were studied using [U-14C]glucose lis marker. Particular attention was given to the synthesis and degradation of the acid-soluble and acid-insoluble glycogen pools.During a 5-h culture period, incorporation into all fractions isolated increased during development from the I-cell to the early blastocyst stage. During maturation of the blastocyst, incorporation into acid-insoluble glycogen fell whilst that into acid-soluble glycogen continued to rise linearly over this 24 h period. At the late blastocyst stage over 80% of total glucose carbon accumulated was in this latter fraction. The decrease in acid-insoluble glycogen observed above was found to occur as a sudden change between 96 and 104 h post-hCG.The turnover of glucose carbon incorporated into the glycogen pools was studied using pulse-chase culture techniques. The results indicate that the considerable amounts of glycogen accumulated at the later stages of preimplantation development cannot act as a major energy source in vitro except in the absence of energy substrates. Under these conditions of energy starvation, however, the breakdown of acid-insoluble glycogen is inhibited.The findings show that the late preimplantation embryo accumulates large amounts of acid-soluble glycogen in vitro due to increased rate of synthesis and low rate of degradation. It is suggested that the falling levels of glycogen reported in the uterine embryo are most likely a result of environment factors other than the availability of energy substrates.Extra keywords: mouse embryo metabolism.

The metabolism of glucose by late pre implantation mouse embryos was studied in a variety of media whose composition had been changed to reflect the environmental conditions in the uterus more closely than do standard culture media. The effects of combinations of energy substrates, the presence or absence of amino acids and the level of potassium in the medium were investigated.The use of energy substrates for in vitro culture at levels present in the uterine environment resulted in rates of synthesis and degradation of glycogen pools similar to those obtained using standard in vitro culture conditions but elevated incorporation into non-glycogen macromolecules. Amino acids influenced the metabolism of glucose by limiting the entry of glucose carbon into the non-glycogen macromolecular pool and directing more glucose into the synthesis of acid-soluble glycogen.Increasing the K + concentration to 60 mM in the culture medium caused a small but significant increase in the number of eight-cell embryos degenerating during culture for 24 h but the metabolism of glucose was unaffected over this time. At the time of morula transformation to the blastocyst this level of potassium ions suppressed glycogen synthesis by 50% over 5 h but did not affect its turnover during chase culture.It is concluded that factors other than those studied here contribute to the maintenance of the low glycogen levels found in uterine embryos. IntrodnctionEarlier work (Ozias and Stern 1973;Ozias and Weitlauf 1971;Snyder et al. 1971;Edirisinghe et al. 1984aEdirisinghe et al. , 1984b indicates that the uterine environment influences the metabolism of late preimplantation mouse embryos and in particular the utilization of glycogen stores. This environment is more complex than, and differs in the range and concentration of components from, the standard chemically defined media normally used for in vitro culture (Hamner 1971;Wales 1973;Beier 1974; Edirisinghe and Wales 1985). Changes in the environment may well be important in modifying the metabolism of glucose by embryos and be responsible for the differences in the turnover of glycogen in vivo as compared to its utilization in vitro.The possible control of glycogen metabolism by the level of exogenous energy substrate has been studied using different concentrations of the major energy substrates, glucose, lactate and pyruvate (Pike and Wales 1982). It is clear from this study that embryos, especially at the late preimplantation stages, have the ability to synthesize large amounts of glycogen and that the presence of the alternative energy substrates, lactate and pyruvate during culture influences the synthesis of glycogen, particularly when the medium contains a low concentration of glucose. Recently, the levels of lactate, pyruvate and glucose in the uterine fluid of mice have been measured and found 0004-9417/85/040411 $02.00

Neither insulin nor epinephrine influenced the incorporation of glucose into the acid-soluble or acid-insoluble glycogen pool of mouse embryos at the morula-early blastocyst stage during 5 h culture in the presence of radiolabelled glucose. During a 5 h chase culture of pulse-labelled embryos at this stage of development, acid-soluble glycogen labelled during the pulse was not utilized by the embryo but acid-insoluble glycogen was reduced. Addition of glucagon, insulin, epinephrine, cAMP, theophylline or caffeine during chase culture had no effect on the turnover of label in the glycogen pools of the embryo. These results indicate that the turnover of embryonic glycogen observed in vivo is not due to the direct effect of the hormones that regulate glycogen metabolism in the mother. Insulin was found to stimulate incorporation of glucose into non-glycogen macromolecules during both pulse and chase culture. Thus, whilst an effect of insulin on glycogen metabolism was absent, the anabolic effects of this hormone appear to have been expressed in the embryo at this stage of development.

No abstract

No abstract