Evaluation of various toxicants in rabbit whole-embryo culture using a new morphologically-based evaluation system

In an effort to advance the use of whole-embryo culture (WEC) techniques in the rabbit, we recently developed a gestational-age-based quantitative morphologic evaluation system for rabbit embryos. In the current study, we applied this new morphological scoring system to assess the development of rabbit gestational day (gd) 9 embryos exposed for 48 hr in WEC to the teratogens ethanol (EtOH, 154 mM), 6-aminonicotinamide (6AN, 0.15 mM), and methoxyacetic acid (MAA, 5.0 mM), and the nonteratogen penicillin G (PG, 2.0 mM). Each teratogen at the concentration tested markedly inhibited morphological development, as indicated by significantly lower morphologic scores (10.1+/-0.05, EtOH; 10.2+/-0.05, 6AN; and 9.8, MAA) relative to controls (10.6+/-0.04), and resulted in an increased percentage of malformed embryos (53%, EtOH; 57%, 6AN; 90%, MAA; and 3%, control). Embryonic growth, as measured by head length, somite number, and total embryonic protein, was significantly decreased by each teratogen. The abnormalities produced by teratogen exposure, which included brain, somite, and facial defects, were often similar to those produced following in vivo exposure in rabbits and rodents, and/or in vitro exposure in rodents. In contrast to the teratogen exposure groups, PG had no effect on embryo growth parameters, or on malformation rate (6%), although a slight but statistically significant decrease in morphology score (10.5+/-0.03) was noted. Our preliminary studies demonstrate the usefulness of the morphology evaluation system by quantifying graded differences in development, and indicate that rabbit WEC may be a useful adjunct to rodent WEC in gaining insights regarding differential interspecies sensitivity.