Hypoxemia represents a major stress for the fetus, and is associated with alterations and adaptations in cardiovascular, metabolic and endocrine responses, which in turn may affect tissue growth and differentiation. To determine the effects of hypoxemia on fetal adrenal activity and growth, we subjected sheep fetuses at days 126-130 and 134-136 (term 145 days) to reduced PaO 2 by reducing the maternal fraction of oxygen for 48 h (mean reduction of 6·8 mmHg), without change in arterial pH or PaCO 2 . This stimulus resulted in similar increases in the plasma immunoreactive ACTH response at both ages. Among adrenal steroids, plasma cortisol (C21 4 ) rose in both groups of animals, but plasma androstenedione (C19 4 ) declined marginally, resulting in a pronounced increase in the cortisol:androstenedione ratio in the plasma that was greater and more sustained in the older fetuses. In the younger fetuses, after 48 h of hypoxemia, there were no significant changes in mRNAs encoding steroidogenic enzymes in the fetal adrenal gland. However, in the older fetuses, hypoxemia resulted in significantly increased levels of mRNAs encoding P450 scc , P450 C21 and 3 -hydroxysteroid dehydrogenase, but not for P450 C17 , in the fetal adrenal gland. Levels of IGF-II mRNA in the fetal adrenal gland fell in both groups of fetuses, and this response was greater at the later gestational age. We conclude that sustained hypoxemia is a potent stimulus which activates adrenal steroidogenesis in the late gestation fetal sheep. The resultant increase in cortisol synthesis is associated with decreased expression of adrenal IGF-II mRNA. We speculate that this relationship might influence patterns of fetal organ growth and differentiative function in response to fetal stress such as hypoxemia.

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Catheters were implanted into 16 ewes and their foetuses between days 110 and 124 of gestation. Hypophysectomy was attempted in eight of these foetuses. Continuous infusion of synthetic ACTH (10 microgram/h) or dexamethasone (1mg/24 h) into the foetus, starting between days 124 and 129, induced premature parturition. The concentration of progesterone in the maternal peripheral plasma decreased before parturition in all animals while the level of oestradiol increased in ewes with intact foetuses or in those in which hypophysectomy was incomplete. When hypophysectomy was complete, no increase in the maternal level of oestradiol occurred before delivery. The concentration of 13,14-dihydro-15-oxo-prostaglandin F2alpha increased in the peripheral plasma of ewes with intact or hypophysectomized foetuses infused with ACTH. It is suggested that an intact foetal pituitary gland is required for the rise in the level of oestrogen prepartum, but that this rise is not essential for increased prostaglandin production of parturition.

In the late-gestation sheep, increased fetal plasma cortisol concentration and placental oestradiol (E 2 ) output contribute to fetal organ maturation, in addition to the onset of parturition. Both cortisol and E 2 are believed to regulate the enzyme 11 -hydroxysteroid dehydrogenase type 1 (11 -HSD1), which interconverts bioactive 11-hydroxy glucocorticoids and their inactive 11-keto metabolites. 11 -HSD1, abundantly expressed in fetal liver, operates primarily as a reductase enzyme to produce bioactive cortisol and thus regulates local hepatic glucocorticoid concentrations. Cortisol acts through the glucocorticoid receptor (GR) present in the liver. In this study, we examined the effects of cortisol and E 2 on hepatic 11 -HSD1 and GR in the liver of chronically catheterized sheep fetuses treated with saline (n=5), cortisol (1·35 mg/ h; n=5), saline+4-hydroxyandrostendione, a P450 aromatase inhibitor (4-OHA; 1·44 mg/h; n=5), or cortisol+4-OHA (n=5). Cortisol infusion resulted in increased plasma concentrations of fetal cortisol and E 2 ; concurrent administration of 4-OHA attenuated the increase in plasma E 2 concentrations. Using immunohistochemistry, we showed that fetal hepatocytes expressed both 11 -HSD1 and GR proteins. Cortisol treatment increased GR in both cytosol and nuclei of hepatocytes; concurrent administration of 4-OHA was associated with distinct nuclear GR staining. Western blot revealed that cortisol, in the absence of increased E 2 concentrations, significantly increased concentrations of 11 -HSD1 (34 kDa) and GR (95 kDa) proteins. 11 -HSD1 enzyme activity was measured in the liver microsomal fraction in the presence of [ + (dehydrogenase activity) respectively. 11 -HSD1 reductase activity was significantly greater in the presence of cortisol. In summary, we found that, in sheep during late gestation, cortisol increased both 11 -HSD1 and GR in the fetal liver, and these effects were accentuated in the absence of increased E 2 .

Extracts of human term amniotic, placental, and chorion/ decidua tissue contained, respectively, 4·36 2·79 (pmol/g wet wt; mean ...; n=5), 2·78 0·5 (n=5) and 0·68 0·68 (n=5) peptide YY (PYY)-like immunoreactivity. Using a specific PYY antiserum, gel filtration chromatography and reverse-phase high performance liquid chromatography (HLPC), amniotic, placental and fetal intestinal tissue extracts were demonstrated to contain PYY-like immunoreactivity consisting of equal amounts of PYY 1-36 and PYY . The presence of pancreatic polypeptide was not detected in any of the extracts.Positive immunohistochemical staining for PYY was seen in extravillous trophoblasts in the decidual septa and fetal membranes, the syncytiotrophoblast and cytotrophoblasts, amniotic epithelial cells and in maternal decidual stromal cells. Positive staining for PYY was found at the earliest date examined (9·5 weeks) and remained present throughout pregnancy to term. PYY and PYY 3-36 may play important roles in human pregnancy, acting via endocrine or paracrine mechanisms.

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