Morphogenetic systems and screening for embryotoxicity.

While mutagenesis appears to be a single-cell phenomenon, the target for teratogenesis are the groups of cell populations constituting the morphogenetic system (MGS). The sensitivity of MGSs is of two kinds. First, it is the sensitivity to general cytotoxic agents. It is non-specific and reaches its maximum during early embryogenesis. The second type of sensitivity manifests itself at the more advanced stages of development, and it is intimately connected with the specific cell differentiation. The basic parameters of embryotoxicity can be estimated from the direct exposure of the selected MGSs both to the test substance and to its metabolites occurring in man. Based upon these principles a rapid and inexpensive screening test (CHEST) has been introduced using the embryonic chick. The test is capable of demonstrating the embryotoxicity effect level, the gross dose-effect relationships as well as estimating the general type of embryotoxic action. The predictive value of this procedure is comparable to that of the current routine techniques. A multilevel combined test for embryotoxicity is proposed in which CHEST is engaged as a priority selection system.