Relationship between blood gas values and hormonal response to acute hypoxemia in fetal sheep.

We examined the relationship of fetal plasma immunoreactive adrenocorticotropic hormone (IR-ACTH), arginine vasopressin (AVP) and cortisol to fetal arterial pO2 (PaO2), oxygen saturation (SaO2), change (delta) in PaO2 (delta PaO2) or SaO2 (delta SaO2) in fetal sheep at 125-139 days of gestational age. Fetal sheep were exposed to two levels of hypoxemia induced by altering the inspired percent oxygen to the mother for 1 h without fetal acidemia. Fetal carotid arterial IR-ACTH, AVP and cortisol concentrations during hypoxemia were correlated with fetal PaO2, SaO2, delta PaO2 and delta SaO2 by applying simple regression analysis. For IR-ACTH, a strong correlation was obtained with SaO2, delta SaO2 and delta PaO2 after log transformation to IR-ACTH. For AVP, strong correlation coefficients were obtained with delta SaO2, SaO2, delta PaO2 and PaO2 after reciprocal transformation to AVP, but for cortisol a strong correlation was obtained only with delta PaO2 after log transformation to cortisol. We conclude that during fetal hypoxemia without acidemia, there is a strong correlation between IR-ACTH and SaO2, delta SaO2, delta PaO2 but not PaO2, between AVP and delta SaO2, SaO2, delta PaO2, or PaO2, and between cortisol and delta PaO2.