An exploration of the role of hydroxyurea injection time in fetal growth and teratogenesis in rats.

Pregnant Wistar rats were injected with hydroxyurea (HU) intraperitoneally (IP) t one of several 6-hour intervals on days 9-10.75 to study the role of circadian growth variations in the teratologic response of the fetuses. Two stocks of rats were studied and the results in each compared. The fetal response to HU, as observed at day 21, was not detectably modified by circadian fetal growth variation. No correlations between hour of HU administration and fetal weight, placental weight, resorption, or total malformation rates were found. Cyclic variations in the incidence of hydronephrosis and left umbilical artery was observed, but it was not clear that these were related to maternal light:dark cycles. Difference of response between two stocks of rats included marked variation in the incidence and type of malformations and variations in the timing of peak incidence for some but not all malformations.