An autoradiographic study on the distribution of the herbicide 4-chloro-2-methylphenoxyacetic acid in pregnant mice

Abstract

Whole body autoradiography was performed after varying intervals from 5 min up to 72 hr following iv injection of [ 14C]4-chloro-2-methylphenoxyacetic acid (MCPA) in pregnant mice. The distribution pattern was characterized by a high concentration in the blood up to 4 hr, and an accumulation in the visceral yolk sac epithelium up to 24 hr after the injection. The radioactive substance passed the placenta, but the fetal tissues never reached the concentration of the maternal tissues. There was no site of accumulation in the fetal tissues. No retention occurred in either the maternal or the fetal tissues 48 hr after the injection. The distribution of [ 14C]MCPA was observed to be similar to that found earlier for [ 14C]2,4-dichlorophenoxyacetic acid (2,4-D) and [ 14C]2,4,5-trichlorophenoxyacetic acid (2,4,5-T). The uptake, however, of [ 14C]-MCPA and [ 14C]2,4-D in the visceral yolk sac was weaker than that of [ 14C]2,4,5-T. These results indicate a teratogenic mode of action for MCPA, similar to the one which has been postulated for 2,4,5-T (i.e., inhibition of the embryotrophic nutrition). It is also possible that a synergistic effect may occur between MCPA, 2,4-D, and 2,4,5-T with respect to their teratogenic action.