Biochemical alterations in skeletal muscle induced by 2,4-dichlorophenoxyacetic butyl ester during chick embryonic development.

2,4-Dichlorophenoxyacetic butyl ester (2,4-D b.e.) (3.1 mg/egg) was applied on fertile hen eggs before starting the incubation. Chicks hatched from treated eggs showed motor dysfunctions, postural troubles and edematous muscles. The electromyography revealed muscular weakness, prolonged motor distal latency, and myotonia. The biochemical composition of leg and complexus muscles from 1-day-old chicks was determined. A significant diminution (24%) in the glycogen level of leg muscles was produced by the treatment. There was a small increase (15%) in sarcoplasmic proteins from leg muscles and an increase of a 20 kD protein in the myofibrillar proteins from complexus muscles. Even though total lipid content was not changed, 2,4-D b.e. treatment produced a diminution of sterol esters (20%) and phosphatidylcholine (11%) and an increase of phosphatidylserine (61%), triglycerides (37%) and free fatty acids (FFA) (448%) in leg muscles. Increases of phosphatidylethanolamine (16%), sterols (58%) and FFA (267%) were detected in complexus muscles. A remarkable increase (700-1500%) of unsaturated FFA, e.g. oleic, linoleic and arachidonic acids, was observed. Considering the avian embryo lipid metabolism, it is proposed that FFA and triglycerides were accumulated because they could not be metabolized in the mitochondria. Since FFA are potent cytotoxic compounds, their increase may be a key factor in the 2,4-D b.e. toxic action in muscle and other tissues during embryonic development.