An ultrasound-guided procedure to administer a label of DNA synthesis intofetal sheep

A novel technique was developed to deliver a bolus dose of a DNA label into the peritoneal cavity of fetal sheep at 85-130 days gestation. Use of mark ers to identify the site of injection in fetuses from litters up to quadrup lets, and immunohistochemistry to detect the DNA label, 5-bromo-2'-deoxyuri dine (BrJU), confirmed the procedure was successful in 85% of cases. Durati on of the procedure was (mean +/- SD) 44 +/- 16 min, and recovery from anae sthesia was rapid and uneventful in ail cases. Fetal weight was estimated w ith a high degree of accuracy (residual standard deviation (RSD) = 297 g an d r(2) = 0.93, P<0.001) and the dose of label administered (110 +/- 33 mg B rdU/kg fetal weight) was adequate in all cases. BrdU detected in fetal nucl ei following injection into amniotic fluid highlights the need for positive identification of the injection site in timed short-term studies, and sugg ests potential to further develop the technique to investigate cellular eve nts in fetal sheep younger than 85 days of gestation. The results demonstra te that the procedure can be used to determine in vivo whether or not nucle i have entered the S-phase of the cell cycle.