Acute hypoxia increases S100beta protein in association with blood flow redistribution away from peripheral circulations in fetal sheep.

We investigated in fetal sheep during late gestation the effects of acute hypoxemia on fetal plasma S100beta protein concentrations and how these relate to fetal redistribution of blood flow and acid-base status. Under general anesthesia, five Welsh Mountain sheep fetuses were instrumented with vascular catheters, and transit-time flow transducers were implanted around a femoral artery and an umbilical artery. At least 5 d after surgery, fetuses were subjected to 1 h of normoxia, 0.5 h of hypoxemia, and 1 h of recovery. Hypoxemia induced significant falls in fetal pH(a), arterial oxygen pressure, acid-base excess, and [HCO(3)(-)], without alteration to arterial partial pressure of carbon dioxide. An increase in arterial blood pressure, a fall in heart rate, an increase in femoral vascular resistance, and a decrease in umbilical vascular resistance occurred in all fetuses. During hypoxemia, plasma S100beta increased significantly and remained elevated until the end of the protocol. Within individual fetuses, plasma S100beta correlated with femoral vascular resistance and pH. In contrast, no relationship was found between S100beta and umbilical vascular resistance. This study reports for the first time that a controlled period of fetal hypoxemia with associated acidemia leads to persistent elevations in plasma S100beta concentrations that strongly correlate with hemodynamic changes that are known to occur during fetal blood flow redistribution. These findings open up a new role for changes in fetal S100beta concentrations as a possible early marker of fetal hypoxia with associated acidemia in perinatal medicine.