The nature of the embryo-protective interaction of propyl gallate with hydroxyurea

Abstract

Hydroxyurea (HU) is a swiftly acting cytotoxic teratogen and an inhibitor of DNA synthesis. Within 2 h of material treatment, HU causes necrosis in proliferating tissues of rabbit embryos on gestational day 12. Co-administration of the antioxidant propyl gallate (PG) delays the onset of necrosis until 6 h and ameliorates the teratogenic effects seen at term. Since HU also causes a rapid, profound decrease in uterine blood flow in pregnant rabbits, it is necessary to determine whether HU and PG interact within the pregnant female or within the embryo. In order to establish that the site of HU-PG interaction is embryonic, HU, PG, HU-PG, or vehicle was injected directly into implantation sites. When embryos were examined microscopically at 4 h, necrosis was observed only in the HU-treated embryos. indicating that the palliative interaction between HU and PG takes place within the embryo. To resolve whether the alleviation of HU-induced embryotoxicity was due to decreased HU levels within HU-PG embryos, HU concentrations were measured in embryos from HU- and HU-PG-treated maternal rabbits at 15 min to 8 h post injection. The HU levels of the two groups differed significantly only at 4 h. The rates of uptake during the linear phase (times from 15 min to 3 h) did not differ. When HU concentration was plotted versus time, measurements of the areas under the curve also did not differ. To determine whether PG alters the HU-induced inhibition of DNA synthesis, 3H-thymidine incorporation into embryonic DNA was assayed at 2 h after HU, HU-PG, or vehicle injections. Both HU and HU-PG treatments produced a 10-fold decrease in 3H-thymidine incorporation relative to controls. These data suggest that the amelioration of HU-induced embryotoxicity as reflected in the delayed onset of necrosis is due to an interaction between HU and PG within the embryo and that the interaction affects neither embryonic HU uptake nor the HU-induced inhibition of DNA synthesis. The results are consistent with the notion that the antioxidant properties of PG may be responsible for the decrease in HU-induced developmental toxicity.