Inhibition of RNA synthesis, a possible mode of the embryotoxic action of hydroxyurea.

14C-u-glucose and 32P-phosphate were given intravenously to pregnant rats, treated and untreated with hydroxyurea (HU). The incorporation of radioactivity into a variety of cell components of the embryo was measured. With this double-labelling technique it is possible to survey the effects of embryotoxic drugs on various pathways in mammalian embryos in vivo. Onset, extent and duration of the metabolic changes were measured after application of "non-teratogenic" and teratogenic doses of hydroxyurea (HU). 3 hrs after application of hydroxyurea only DNA synthesis is affected, whereas after 5 hrs RNA synthesis is also inhibited.