To study the consequences of atrazine exposure during organ morphogenesis, McLaughlin and her colleagues, Professor of Biology J. Michael Reed, doctoral candidate Jenny R. Lenkowski and Lisa Deininger, a Summer Scholars program undergraduate student, collected eggs from adult female frogs and then fertilized them in vitro. Scientists exposed the developing tadpoles to 10, 25 and 35 mg/L of atrazine. The 35 mg/L dosage simulated the average amount of herbicide used when it is applied in the field, said McLaughlin.
Twelve to 24 hours after exposure to atrazine, tadpoles were examined for abnormal heart growth, visceral hemorrhaging, intestinal coiling, edema and apoptosis (normal cell death that is "programmed" by the body).
Compared with control populations, the tadpoles that were exposed to atrazine had a dramatically higher incidence of abnormalities. The degree of deformities generally corresponded to the size of the dose. After 48 hours of exposure, the point at which organ development is disrupted most profoundly, 57 percent of the tadpoles exposed to 35 mg/L of atrazine had hearts that were smaller than normal, compared with 2% to 3% for the two control groups.
Ectopic Cell Death
The Tufts scientists also examined atrazine exposed tadpoles for increased incidence of apoptosis by measuring levels of active caspase-3 in the pronephric kidney and midbrain. Caspase-3 is a protein needed for apoptosis to occur. They conducted measurements after 6, 12, 24 and 48 hours of exposure in tadpoles exposed to 25 and 35 mg/l of atrazine. Researchers observed that the atrazine-exposed tadpoles showed significant increases in caspase-3 levels in the kidney and midbrain at 12 hours and beyond when compared with controls. The findings indicated a high incidence of ectopic, or abnormal, apoptosis.
"The increased levels of apoptosis in th
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