The incorporation of fixed carbon from carbon dioxide into mouse embryos was greatest in eight-cell embryos which developed into blastocysts during a 24-hr culture period and was four to five times greater than the incorporation into two-cell embryos cultured for a similar period. The net accumulation of labelled products in the culture medium was greatest during the culture of the morula stage to the blastocyst over 24 hr.

The chemical composition of uterine fluid collected from ewes cannulated by three different procedures was studied.Sodium and chloride were the major inorganic ions present. Smaller amounts of potassium, magnesium, calcium, ammonium, bicarbonate, and phosphate ions were also found. Orcinol-reactive carbohydrate was present in high concentration but only 1--4 % could be accounted for as the reducing sugar, glucose. Approximately 5 mM lactate was present in the uterine secretions.Protein concentration varied from 1 to 3 g/loo ml and some differences existed between uterine fluid and blood serum both in electrophoretic mobility and relative concentration of the various protein components. Uterine fluid also differed in amino acid composition from blood serum and the results suggest that uterine fluid is, at least in part, a true secretion and not merely a blood transudate.Differences in chemical composition between stages of the oestrous cycle were small and only minor differences were found between fluid collected from the uterine horn and that collected from the body of the uterus. By contrast the composition of fluid collected from ewes with a cannula inserted through the cervical canal differed considerably from that of fluid collected by the other two methods of cannulation and the former method may give a less reliable estimate of the true uterine environment.

SummaryThe effects of potassium, magnesium, calcium, phosphate, and sulphate ions on the development of two-cell mouse embryos to blastocysts were investigated.Both potassium and calcium ions are necessary for development and no blastocysts were formed in the absence of either of these ions. Normal development can occur in the presence of a wide range of concentration of potassium or calcium ions but at least 0·8 mM potassium and 0·4 mM calcium in the medium were necessary to obtain a large proportion of blastocysts. Lower concentrations of potassium suppressed cleavage. Oulture in calcium-deficient media led to a decrease in the rate of cleavage and an apparent breakdown of intercellular binding.Magnesium and phosphate ions were less important and even in the complete absence of these ions development into blastocysts could occur although the percentage of embryos forming blastocysts was decreased. Absence of sulphate ions did not affect the number of blastocysts developing.

SummaryA method is described by which sufficient spermatozoa can be separated rapidly from their incubation medium to assay individual metabolites accumulating from [U· 14 C]fructose. Acetate and lactate made up 60-80% of the substrate carbon accumulated within the cell. Acetate was the main intracellular metabolite and its concentration in the cell was 10-20 times its extracellular level. The intracellular accumulation of lactate varied with the period of incubation but its concentration in the cell was always below that in the medium. The remaining substrate carbon in the cell was made up of fructose and at least three other unidentified compounds. No accumulation of substrate carbon was detected in citric acid cycle intermediates.The intracellular accumulation of metabolites was unaffected by the presence or absence of metabolic carbon dioxide during incubation. While lactate production was decreased by a restriction in the availability of substrate to the cell, acetate accumulation was unaffected. It is suggested that acetate acts as an intracellular substrate pool for entry into the citric acid cycle.

No abstract