Effect of gestational age and hypoxia on activity of ribonucleic acid polymerase in fetal guinea pig brain

OBJECTIVE: The aim of this study was to determine the effect of gestational age and hypoxia on the activity of ribonucleic acid polymerase in fetal gu inea pig brain. STUDY DESIGN: Fetal cerebral cortical neuronal nuclei were isolated at 40, 50, and 60 days (term) of gestation to determine the effect of gestational age on the activity of ribonucleic acid polymerase I, II, and III. Pregnant guinea pigs at 60 days' gestation were randomly assigned to a normoxic or hypoxic group to determine the effect of hypoxia on ribonucleic acid polyme rase activity. The fetal neuronal nuclei were pooled from 6 pregnant animal s in each group. In the normoxic group the pregnant guinea pigs were expose d to room air before delivery. In the hypoxic group delivery occurred after the pregnant guinea pig had been exposed to 7% oxygen for 60 minutes. The fetuses were delivered by cesarean, and the fetal cerebral cortical neurona l nuclei were isolated immediately. Ribonucleic acid polymerase activity wa s determined with nuclei suspended in a buffer containing adenosine triphos phate, guanosine triphosphate, cytidine triphosphate, and tritiated uridine triphosphate. Dactinomycin (actinomycin D) and polydeoxyadenylic-thymidyli c acid were used to determine the activity of bound and free ribonucleic ac id polymerase. a-Amanitin was used to determine the activity of ribonucleic acid polymerase II. RESULTS: The activity of total (bound and free) ribonucleic acid polymerase I and III increased from 85.4 +/- 9.4 fmol of tritiated uridine triphospha te incorporated per milligram of protein per hour at 40 days' gestation to 233.3 +/- 82.1 fmol at 50 days and to 343.4 +/- 231.6 fmol at 60 days (P = .02). Total ribonucleic acid polymerase II activity increased from 19.9 +/- 6.0 fmol of tritiated uridine triphosphate incorporated per milligram of p rotein per hour at 40 days to 123.8 +/- 53.0 fmol at 50 days and to 200.9 /- 77.8 fmol at 60 days (P < .01). In the term fetal guinea pig brain the a ctivity of bound ribonucleic acid polymerase I and III decreased from 116.8 <plus/minus> 107.2 fmol of tritiated uridine triphosphate incorporated per milligram of protein per hour under normoxic conditions to 92.8 +/- 76.0 f mol in hypoxic fetal brain, a decrease of 20.5%. Free ribonucleic acid poly merase I and III activity decreased from 199.2 +/- 115.2 fmol of tritiated uridine triphosphate incorporated per milligram of protein per hour in norm oxic fetal brain to 132.0 +/- 66.4 fmol in hypoxic fetal brain, a decrease of 33.8%. Free ribonucleic acid polymerase II activity decreased from 62.4 +/- 70.4 fmol of tritiated uridine triphosphate incorporated per milligram of protein per hour in normoxic fetuses to 13.6 +/- 9.6 fmol in hypoxic fet al brain, a decrease of 78.2%. In contrast, however, in term fetal guinea p ig brain, bound ribonucleic acid polymerase II activity increased from 8.0 +/- 10.4 fmol of tritiated uridine triphosphate incorporated per milligram of protein per hour under normoxic conditions to 35.2 +/- 8.8 fmol in hypox ic fetal brain, an increase of 340% (P < .01). CONCLUSION: The activity of ribonucleic acid polymerases I, II, and III inc reases throughout the latter half of gestation, from 40 to 60 days, in the fetal guinea pig brain. Hypoxia in utero is associated with a decrease in r ibonucleic acid polymerase I and III activity. Although hypoxia is associat ed with a decrease in free ribonucleic acid polymerase II activity, we obse rved a marked increase in bound ribonucleic acid polymerase II activity. wh ich may represent a hypoxia-induced alteration of gene expression.