title: Topical dose delivery in the reptilian egg treatment model.
abstract: Developing assays to detect endocrine-mediated toxicity from in ovo or in utero exposure is a current challenge in regulatory toxicology. Some species of reptiles exhibiting a unique mode of sex determination, in which the incubation temperature during a critical period determines gonadal sex, have been explored as an in ovo model to screen environmental contaminants for endocrine effects. We critically review published egg-exposure studies and conclude that data regarding the pharmacokinetics of topically applied substances are insufficient to validate dose-response relationships for the effects of chemicals on in ovo endocrine function or gender determination in reptiles. The insufficiencies in these data largely result from methodological failures, including lack of measurement verification, failure to investigate and control extraneous factors affecting the measurements, and lack of independent replication of results. Considerable additional research will be necessary to alleviate these methodological inadequacies. Given the current status of the data, topical treatment of reptilian eggs cannot be considered to be a valid means of establishing causal relationships between chemical treatment and biological outcome.
authors.affiliation: Applied Pharmacology and Toxicology, Inc., 2250 Northwest 24th Avenue, Gainesville, Florida 32605, USA.
authors.forename: Jennifer K
authors.initials: JK
authors.lastname: Muller
authors.forename: Timothy S
authors.initials: TS
authors.lastname: Gross
authors.forename: Christopher J
authors.initials: CJ
authors.lastname: Borgert
mesh_terms: D000287:Administration, Topical; D000818:Animals; D004305:Dose-Response Relationship, Drug; D052244:Endocrine Disruptors / Q000008:administration & dosage / Q000493:pharmacokinetics / Q000633:toxicity*; D004703:Endocrine System / Q000187:drug effects*; D004785:Environmental Pollutants / Q000008:administration & dosage / Q000493:pharmacokinetics / Q000633:toxicity*; D006066:Gonads / Q000187:drug effects* / Q000196:embryology; D008954:Models, Biological; D010063:Ovum / Q000187:drug effects* / Q000378:metabolism; D012104:Reptiles; D012732:Sex Determination Analysis; D012733:Sex Differentiation / Q000187:drug effects* / Q000502:physiology; D013696:Temperature; D016896:Treatment Outcome
chemical_list: D052244:Endocrine Disruptors; D004785:Environmental Pollutants