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Summary.

Adult female rats injected subcutaneously with 100 mg aminoglutethimide phosphate (AGP)/kg/day for 4 weeks failed to become pregnant when placed in cohabitation with males during the last 2 weeks of the injection period. Lower doses depressed the fertility rate and reduced the litter size: the average litter size of three of eleven rats given 50 mg/kg/day was 4·7 young and of four of eleven rats given 25 mg was 7·0 young. Twenty-nine controls averaged 10·1/litter. Doses of 100 mg AGP/kg/day stopped vaginal cycling, prevented ovulation in adults, and delayed dissolution of the vaginal membrane in pubertal rats. Histological studies of the ovaries from rats with initial ages of 17 or 21 days which were injected with 25 to 100 mg AGP/kg/day for 2 weeks showed an increase in the number and size of vesicular follicles. Treatment of 27-day-old rats with 25 mg/kg/day for 2 weeks reduced the number of CL and three of four rats given 50 mg had ovaries lacking such bodies; all control ovaries in this group contained CL. These findings are taken as evidence that AGP inhibits ovulation but does not prevent follicular maturation.

The consumption of oxygen, uptake of pyruvate and glucose and production of lactate were determined for groups of bovine embryos produced in vitro from the one-cell to the blastocyst stage (day 0–6 of culture). Measurements were made in Hepes-buffered synthetic oviduct fluid medium supplemented with 1.0 mmol pyruvate l⁻¹, 10 mmol d,l-lactate l⁻¹ and 1.5 mmol glucose l⁻¹ and also 3 mg BSA ml⁻¹ and, from day 5 of development, 10% (v/v) fetal calf serum. The amount of ATP production was determined from oxygen consumption and the proportion of glucose taken up that could be accounted for by lactate production. The data revealed that oxygen consumption was relatively constant from days 0–4 of culture (0.24–0.27 nl per embryo h⁻¹), but increased with the initiation of compaction (0.39 nl per embryo h⁻¹) and continued to increase with the formation and expansion of the blastocoel (0.9 nl per embryo h⁻¹). Both pyruvate and glucose uptake followed similar patterns. Furthermore, when plotted against oxygen consumption, both pyruvate and glucose uptake increased significantly (P < 0.001) in a linear relationship (R ² = 0.61 and 0.49, respectively). Lactate production also increased with development and accounted for 40% of glucose uptake at day 0 of culture (putative zygotes), increasing to 70% by day 2 (eight-cell stage) and 100% of glucose uptake from day 4 of culture onwards. ATP production followed a similar pattern to that of oxygen consumption (60–85 pmol per embryo h⁻¹ from day 0 to day 4) increasing with compaction (124 pmol per embryo h⁻¹) and blastulation (221 pmol per embryo h⁻¹). For precompaction stages, 93–96% of ATP production was derived from oxidative phosphorylation, decreasing to 82% with compaction. ATP produced by oxidative phosphorylation could be accounted for by the uptake of pyruvate, suggesting that bovine embryos produced in vitro utilize little endogenous substrates when appropriate exogenous substrates are present in the culture medium. The data revealed that bovine embryos were dependent on oxidative phosphorylation for energy (ATP) production at all stages of pre-elongation development, with perhaps a shift in dependence towards glycolysis in conjunction with compaction. It follows that oxidizable substrates, such as pyruvate and certain amino acids, are preferred in embryo culture medium during development in vitro.

The cyclic nucleotides, cAMP and cGMP, are the key molecules controlling mammalian oocyte meiosis. Their roles in oocyte biology have been at the forefront of oocyte research for decades, and many of the long-standing controversies in relation to the regulation of oocyte meiotic maturation are now resolved. It is now clear that the follicle prevents meiotic resumption through the actions of natriuretic peptides and cGMP – inhibiting the hydrolysis of intra-oocyte cAMP – and that the pre-ovulatory gonadotrophin surge reverses these processes. The gonadotrophin surge also leads to a transient spike in cAMP in the somatic compartment of the follicle. Research over the past two decades has conclusively demonstrated that this surge in cAMP is important for the subsequent developmental capacity of the oocyte. This is important, as oocyte in vitro maturation (IVM) systems practised clinically do not recapitulate this cAMP surge in vitro, possibly accounting for the lower efficiency of IVM compared with clinical IVF. This review particularly focuses on this latter aspect – the role of cAMP/cGMP in the regulation of oocyte quality. We conclude that clinical practice of IVM should reflect this new understanding of the role of cyclic nucleotides, thereby creating a new generation of ART and fertility treatment options.

In adult ewes, we tested whether ovarian function, including the response to short-term supplementation, was affected by the nutrition of their mothers during the pre-/post-natal period. A 2×2 factorial design was used with nutrition in early life (low or high) and a 6-day supplement (with or without) as factors. All ewes received three prostaglandin (PG) injections 7 days apart, and the supplement (lupin grain) was fed for 6 days from 2 days after the second until the third PG injection. We measured reproductive and metabolic hormones, studied follicle dynamics (ultrasonography), and evaluated granulosa cell numbers, aromatase activity and oestradiol (E₂) concentrations in follicular fluid in healthy follicles at days 3 and 7 of supplementation. Ovulation rate was increased by 25% by exposure to high pre-/post-natal nutrition (1.5 vs 1.2; P<0.05), in association with a small decrease in FSH concentrations (P=0.06) and a small increase in insulin concentrations (P=0.07). The number of healthy antral follicles was not affected. Acute supplementation increased the number of granulosa cells (3.7±0.2 vs 3.0±0.2 million; P<0.05) in the largest follicle, and the circulating concentrations of E₂ (4.6±0.3 vs 3.9±0.3 pmol/l; P<0.05) and glucose (3.4±0.03 vs 3.3±0.03 mmol/l; P<0.01). Both early life nutrition and acute supplementation appear to affect ovulation rate through changes in glucose–insulin homoeostasis that alter follicular responsiveness to FSH and therefore E₂–FSH balance.