TISSUE DNA-SYNTHESIS IN THE PRETERM OVINE FETUS FOLLOWING 8 HOURS OF SUSTAINED HYPOXEMIA

OBJECTIVE: Protein synthesis is significantly decreased in the near-te rm ovine fetus in response to induced hypoxemia of several hours' dura tion. We therefore sought to determine the extent to which DNA synthes is rates as an index of tissue mitotic activity are also affected by s imilarly induced compromises in fetal oxygenation. METHODS: Fetal shee p were studied at 0.75 of gestation during a normoxic control period a nd an 8-hour experimental period of either sustained hypoxemia induced by lowering maternal inspired oxygen concentration of 11-8% (hypoxia group, n = 7) or continued exposure to room air (control group, n = 5) . To estimate DNA synthesis rate, [H-3]-thymidine (1 Mci/kg) was injec ted intravenously into each fetus at the beginning of the experimental period. RESULTS: Sustained hypoxemia with a reduction in fetal arteri al O-2 content from (mean +/- standard error of the mean) 4.3 +/- 0.1 to 1.5 +/- 0.1 mmol/L by the end of study resulted in a variable degre e of fetal acidemia, 7.26 +/- 0.03 (range from 7.41 to 7.10), which wa s entirely metabolic in nature. CONCLUSION: The DNA synthesis rates of most tissues were not significantly changed by the 8 hours of sustain ed hypoxemia, suggesting that restrictions in protein synthesis in res ponse to fetal hypoxia are initially due to a differential effect on n onmitotic synthetic processes at this stage of development. However, s elective decreases in the DNA synthesis rates of the hippocampus (appr oximately 50%, P < .01), adrenals (approximately 48%, P < .05), and le ft and right myocardial ventricles (approximately 42% and 27%, respect ively, P = .08) were evident which may reflect altered mitotic activit y in response to tissue related changes in energy expenditure. Copyrig ht (C) 1997 by the Society for Gynecologic Investigation.