Fetal endocrinological responses to chronic hypoxemia are useful in elucidating the process of growth restriction at earlier stages of fetal development. The purpose of this study was to observe endocrinological responses to prolonged (24-h) non-acidemic hypoxemia in preterm goat fetuses. Fetal hormonal changes were examined in chronically instrumented goat fetuses at gestational day 96-102 (0.7 gestation) during continuous nitrogen infusion into the maternal trachea to create prolonged fetal hypoxemia. Plasma levels of arginine vasopressin (AVP), epinephrine, norepinephrine, adrenocorticotropic hormone (ACTH) and cortisol were measured, along with fetal heart rate (FHR) and fetal blood pressure (FBP). Fetal arterial pO(2) declined significantly from 25.0 +/- 1.0 mmHg at baseline to 15.3 +/- 1.0 mmHg after 2 h of hypoxemia, then remained at this level. FHR increased significantly throughout the experiment, but FBP remained unchanged. AVP and ACTH levels rose significantly after 2 h of hypoxemia, and declined to the control values after 12 h. There was no significant increase in the epinephrine level during 24-hr hypoxemia. In contrast, norepinephrine significantly increased after 2 h of hypoxemia and remained at the elevated levels throughout the remainder of the experiment. Thus, preterm fetuses could respond to acute hypoxic stress by increasing the plasma levels of AVP, norepinephrine and ACTH. However, despite the rapid increase in ACTH, the level of cortisol in the fetal plasma was significantly elevated only after 18 h of hypoxemia. The chemoreceptors of preterm fetuses, which regulate the release of cortisol or epinephrine, may be less sensitive to hypoxic insults.