Abstract
The behaviour of some pyrimidine thioanalogs has been studied on in vitro fibroblasts from chick embryo heart. 4 out of the 7 tested substances showed a typical inhibiting action on cytodieresis, and namely:
2-thio-5-methyl-cytosine, 2-thio-4-methyl-aminopyrimidine, 2-methyl-thio-5-bromo-cytosine and 2-6-dithio-thymine. Three of them proved to be aspecifically toxic: 2-thiocytosine, 2-thio-4-oxycytosine and 2-6-dithio-uracil.
Cytodieresis is inhibited by intermediate concentrations, higher concentrations blocking mitosis of the interkinetic nuclei. This action results in the formation of multinuclear elements with syncytial aspect. Low concentrations induce chromosomal alterations with atypical mitotic pictures (picnosis, fragmentation, stickiness) and alterations of nucleoli which are enlarged and show morphological abnormalities.
In the search of possible correlations between mitotic and biochemical alterations during the interkinetic phase, a study has been carried out in order to prove the microbiologic finding of an antagonism from folic acid and thymine. Folic acid was found to be unable to antagonize effectively the action of all the tested inhibitors.
Thymine, which at high concentrations behaves as cytodieresis inhibitor, allows the growth recover with increasing number of mitoses; the picture of cytodieresis inhibition is unmodified.
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