Changes in hypoxanthine and lactate during and after hypoxia in the fetal sheep with chronically-implanted vascular catheters.

The effect of intra-uterine hypoxia on the hypoxanthine and lactate concentration in fetal sheep with catheters chronically implanted was investigated. Experiments were conducted on five fetuses. Sixty-four blood samples from nine hypoxic and recovery periods were analysed. A significant increase of hypoxanthine and lactate occurred in parallel with the fall of arterial oxygen saturation (SaO2) and arterial oxygen pressure (PaO2) during the first 20 min of hypoxia. The elevations in plasma hypoxanthine and lactate were significantly greater during more severe hypoxia than mild hypoxia, as judged from the amount of low oxygen gas mixture given to the ewe (7 or 9%). There were no difference in PaO2 and only minor difference in SaO2 between the two groups. The increase in lactate over 20 min was the same throughout the one-hour period of hypoxia, while the increase of hypoxanthine was less pronounced at the end of the period. This might be due to the fact that hypoxanthine was cleared from fetal plasma at a fairly rapid rate, half of the excess concentration being eliminated after 25 +/- 21 min compared to 85 +/- 47 min for lactate in six experiments post hypoxia. Linear regression analysis revealed a highly significant correlation between hypoxanthine and SaO2, pH and lactate (P less than 0.001). These three variables explained 77% of the variance of hypoxanthine, when calculated by multiple regression analysis.