Application of the Hydra Assay for Rapid Detection of Developmental Hazards

Abstract

Adult hydra and artificial “embryos” composed of randomly reaggregated cells of dissociated hydra were exposed to test chemicals. The lowest concentration killing adult hydra became the numerator, and the lowest concentration disrupting development of “embryos” became the denominator of a ratio. This adult toxic (A) to developmentally toxic (D) or A/D ratio from hydra was compared to the A/D ratio calculated from published reports employing standard laboratory animals. Data from rodents were considered if both adult and developmental toxicities were consistent for: species, route, and duration of treatment and had a direct dose-response relationship indicating that the toxic manifestations were near the low end of a dose-response curve. The minimal expression of adult toxicity was usually loss in body weight, but developmental toxicity varied from abnormal development or death to reduced fetal weight. The hydra assay proved as effective as standard safety evaluations in rodents at detecting developmental hazards, i.e., substances capable of disrupting the conceptus at a small fraction of the minimal dose toxic to adults. It also was as effective as rodents in establishing that the majority of substances are capable of disrupting development of the conceptus only at doses also toxic to adults.