Does tributyl phosphate influence the radiation risk of a highly proliferating system--the early mouse embryo in...

Two-cell mouse embryos were exposed in vitro to tributyl phosphate, x rays, or a combination of both. In-vitro development of the embryos was followed microscopically (cleavage to four- and eight-cell embryos, formation of morulae and blastocysts, and hatching of blastocysts). Effects on proliferation were estimated by counting the number of cells per embryo early (48 h p.c. = 48 hours post conceptionem) and late (144 h p.c.) in the preimplantation period. Cytogenetic damage was studied using micronucleus formation as the end point. Tributyl phosphate did not reveal toxic effects up to a concentration of about 5 microM after an exposure time of 18 h. At a concentration of about 15 microM, 50% of late preimplantation embryos showed effects on morphological development and on cell proliferation, and at about 40 microM, 90% of the embryos were affected. Tributyl phosphate did not induce micronuclei. Small effects by x irradiation were observed between 0.25 Gy and 0.5 Gy, depending on the end point measured in the late preimplantation stage. Fifty percent of the embryos were affected by a dose slightly higher than 1 Gy, and 90% after about 4 Gy. No enhancement in risk was found after combined treatment of the embryos with tributyl phosphate and x rays.