Akagi K, Berdusco E T, Challis J R
Department Obstetrics and Gynaecology, University of Western Ontario, Lawson Research Institute, St. Joseph's Health Centre, London, Canada.
J Dev Physiol. 1990 Dec;14(6):319-24.
During acute hypoxemia in fetal sheep the elevation in ACTH concentration in the fetal circulation at days 125-129 is greater than that at term, but similar rises in AVP occur at both times. To examine whether the diminished ACTH response is due to elevated endogenous cortisol, and if there is differential control of ACTH and AVP release in hypoxemia, we infused either vehicle or cortisol (5 micrograms/min) into fetal sheep at days 123-128 for 5 h before and then during a 2-h period of acute hypoxemia (mean PaO2 decrease 8.2 mmHg) without acidemia. During cortisol infusion, plasma cortisol rose to 40-50 ng/ml, similar to values in term fetuses. In vehicle-infused fetuses, cortisol rose from 2.1 to 7.0 ng/ml at +1 to +2 h of hypoxemia. ACTH rose significantly during hypoxemia in the vehicle-infused fetuses, and this response was attenuated by cortisol infusion. In contrast, fetal AVP rose significantly during hypoxemia both in the presence and absence of cortisol infusion. Fetal breathing movements, and electroocular activity decreased during hypoxemia, and these responses were not altered by cortisol. We conclude that cortisol exerts differential negative feedback on ACTH but not on AVP release during hypoxemia. The maintained AVP response may facilitate cardiovascular adjustments of the fetus to hypoxemia even when endogenous cortisol is elevated, such as near term.
在胎羊急性低氧血症期间，妊娠125 - 129天时胎循环中促肾上腺皮质激素（ACTH）浓度的升高幅度大于足月时，但抗利尿激素（AVP）在这两个时期的升高幅度相似。为了研究ACTH反应减弱是否归因于内源性皮质醇升高，以及在低氧血症时ACTH和AVP释放是否存在差异调控，我们在妊娠123 - 128天时，于急性低氧血症（平均动脉血氧分压下降8.2 mmHg）且无酸血症的2小时期间之前及期间，向胎羊输注溶媒或皮质醇（5微克/分钟），持续5小时。在输注皮质醇期间，血浆皮质醇升至40 - 50纳克/毫升，与足月胎儿的值相似。在输注溶媒的胎羊中，低氧血症1至2小时时皮质醇从2.1纳克/毫升升至7.0纳克/毫升。在输注溶媒的胎羊中，低氧血症期间ACTH显著升高，而这种反应因输注皮质醇而减弱。相反，无论是否输注皮质醇，低氧血症期间胎羊AVP均显著升高。低氧血症期间胎羊呼吸运动和眼球电活动减少，且这些反应不受皮质醇影响。我们得出结论，在低氧血症期间，皮质醇对ACTH释放发挥差异性负反馈作用，但对AVP释放无此作用。即使内源性皮质醇升高，如接近足月时，AVP反应的维持可能有助于胎儿对低氧血症进行心血管调节。
