Evidence from epidemiologic, clinical, and experimental studies has shown that a suboptimal intrauterine environment during early pregnancy can alter fetal growth and gestation length and is associated with an increased prevalence of adult hypertension and cardiovascular disease. It has been postulated that maternal nutrient restriction may act to reprogram the development of the pituitary-adrenal axis, resulting in excess glucocorticoid exposure and adverse health outcomes in later life. It is unknown, however, whether maternal nutrient restriction during the periconceptional period alters the development of the fetal pituitary-adrenal axis or whether the effects of periconceptional undernutrition can be reversed by the provision of an adequate level of maternal nutrition throughout the remainder of pregnancy. We have investigated the effect of restricted periconceptional nutrition (70% of control feed allowance) from 60 days before until 7 days after mating and the effect of restricted gestational nutrition from Day 8 to 147 of gestation on the development of the fetal hypothalamo-pituitary adrenal (HPA) axis in the sheep. In these studies, we have also investigated the effects of fetal number and sex on the pituitary-adrenal responses to periconceptional and gestational undernutrition. In ewes maintained on a control diet throughout the periconceptional and gestational periods, fetal plasma ACTH concentrations were higher and the prepartum surge in cortisol occurred earlier in singletons compared with twins. Plasma ACTH concentrations were also significantly higher in male compared with female singletons, and in twin fetuses, the prepartum surge in cortisol concentrations occurred earlier in males than in females. Periconceptional undernutrition resulted in higher fetal plasma concentrations of ACTH between 110 and 145 days of gestation and a significantly greater cortisol response to a bolus dose of corticotropin-releasing hormone in twin, but not singleton, fetuses in late gestation. We have therefore demonstrated that fetal number and sex each has an impact on the timing of the prepartum activation of the HPA axis in the sheep. Restriction of the level of maternal nutrition before and in the first week of a twin pregnancy results in stimulation of the fetal pituitary-adrenal axis in late gestation, and this effect is not reversed by the provision of a maintenance control diet from the second week of pregnancy.
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