The Action of Aminopterin on the Explanted Early Chick Embryo

One method of gaining insight into the mechanisms of growth and differentiation is based on the use of defined substances to alter normal development, but analysis of developmental changes so produced may be difficult or impossible if the substances used have an ill-defined biochemical action. The antimetabolites, however, do not have this disadvantage and, among them, folk acid antagonists are especially interesting. The metabolic activity of folic acid, which has been demonstrated in microorganisms, insects and vertebrates, is inhibited by suitable doses of folic acid antagonists. Because therapeutically they cause temporary remissions in cases of acute leukaemia, probably more analogues of folic acid have now been developed than of all other vitamins put together (Daniel, 1961). Aminopterin (4-aminopteroyl-L-glutamic acid) has been widely used, although the less potent methotrexate (amethopterin) (4-amino-10-methylpteroyl-L-glutamic acid) has often been preferred clinically.