Drug-induced changes of rRNA biosynthesis--a marker of toxic damage to embryonal cell population.

The nucleolar test was used for evaluation of the rRNA biosynthesis in two populations of chick embryonic cells. In chick embryos, practically 100 per cent of proerythroblasts (starting from embryonic day 3) as well as hepatocytes (starting with embryonic day 5) synthetized nucleolar, i.e. ribosomal RNA. In consequence of a single administration of the well known teratogens--actinomycin D, cyclophosphamide or hydrocortisone--the percentage of rRNA synthetizing proerythroblasts and hepatocytes decreased characteristically--in dependence on the teratogenic drug. The presented method can be employed when toxicity of drugs or other chemical compounds is evaluated in cell populations possessing high metabolic and proliferative activity.