AbstractIn vitro culture of rodent embryos has been extensively used in the search for teratologic agents, with possible relevance to diabetic pregnancy. However, the high concentrations of rat serum added to the culture medium (∼75%) have raised concern that the teratogenic effects of some compounds may be attenuated or masked in this culture system and thereby forced the addition of pharmacological concentrations of the compounds (e.g.,D‐glucose and β‐hydroxybutyrate) to the medium. This issue has been examined in the present study where the effects of different concentrations of rat serum on growth and differentiation of rat embryos were recorded in cultures supplemented with increased concentrations ofD‐glucose and β‐hydroxybutyrate. The embryonic development was also evaluated after culture in medium supplied with serum from diabetic rats. Compared with normal rat serum, the diabetic serum had an elevated glucose concentration as well as markedly increased levels of triglycerides and branched amino acids, indicating a potentially rich supply of major nutrients for the cultured embryos.Lowering the serum concentration in the culture medium from 80% to 50% yielded progressively retarded embryonic growth but no increased rate of other morphological malformations. At 40% serum concentration, however, there was a sharp rise in the incidence of somatic malformations, in addition to the prevailing growth retardation. When the embryonic growth and development were compared at 50% and 80% serum concentrations, increasedD‐glucose or β‐hydroxybutyrate concentrations caused similar degrees of embryonic dysmorphogenesis. Also, the uptake of each compound by the embryos exposed to elevated levels of the two agents were similar in 50% and 80% serum cultures. There was, therefore, no protection against the teratogenic and growth‐retarding effects of increasedD‐glucose or β‐hydroxybutyrate offered by high serum concentrations in the culture medium (i.e., 80% vs. 50%).Embryos cultured in 50% or 80% diabetic rat serum at 30 mmol/L or 50 mmol/LD‐glucose concentration showed similar rates of somatic malformations as did embryos exposed to the same proportion of normal rat serum at similar glucose concentrations. By contrast, the diabetic rat serum amplified the general retarding effects of highD‐glucose levels, yielding lower protein levels and somite numbers in embryos from diabetic serum culture than in embryos cultured in normal rat serum. This effect was achieved despite slightly lower uptake of glucose in embryos cultured in diabetic serum compared to embryos cultured in normal serum (at high glucose and similar serum concentrations). The embryos exposed to elevated levels of β‐hydroxybutyrate in diabetic serum, however, showed slightly enhanced uptake of the ketone body. These findings suggest that diabetic serum alters the embryonic transport of the teratogenic compoundsD‐glucose and β‐hydroxybutyrate. The present study implicates that embryonic development in a diabetic environment can be further studied with the present experimental design, perhaps with the addition of new methods for evaluation of