Grantee Research Project Results
2003 Progress Report: Impact of Phthalates on the Male: Frog and Rabbit Models
EPA Grant Number: R829429Title: Impact of Phthalates on the Male: Frog and Rabbit Models
Investigators: Veeramachaneni, D. N. Rao
Institution: Colorado State University
EPA Project Officer: Aja, Hayley
Project Period: March 1, 2002 through February 28, 2005 (Extended to February 28, 2007)
Project Period Covered by this Report: March 1, 2003 through February 28, 2004
Project Amount: $852,709
RFA: Children's Vulnerability to Toxic Substances in the Environment (2001) RFA Text | Recipients Lists
Research Category: Children's Health , Human Health , Environmental Justice
Objective:
The objective of this research project is to test the hypothesis that exposure to dibutyl phthalate (DBP) during differentiation of the reproductive system, even at relatively low concentrations, alters reproductive function as adults. This hypothesis is being tested in two animal models, an amphibian, Xenopus laevis, and a nonrodent mammal, the rabbit. The former facilitates transdermal exposure and evaluation of an easy-to-monitor, unique thyroid hormone-dependent event, the metamorphosis, whereas the latter facilitates longitudinal evaluations of hormones, semen parameters, and sexual capacity. Furthermore, rabbits, unlike rodents, have a relatively long infantile period of reproductive development more closely approximating the situation in humans. The dermal route of exposure is particularly pertinent to children’s vulnerability to toxic substances in the environment because children have a greater ratio of surface area to body weight than adults.
Progress Summary:
Except for one replicate, animal phases of all experiments for the rabbit component have been completed.
For the frog component of these studies, animal phases of all three experiments utilizing the X. laevis model and analytical phases of two experiments have been completed.
Experiment 1
Frog Embryo Teratogenesis Assay-Xenopus: Xenopus embryos were exposed to 0, 0.1, 0.5, 1, 5, 10, and 15 ppm DBP during the first 4 days of life when major organs differentiate and developmental effects were evaluated. DBP, at a concentration as low as 0.1 ppm, inhibited the growth of tadpoles. The lowest concentrations that caused death or a malformation in 50 percent of the population were found to be 14.5 ppm and 0.98 ppm, respectively.
Experiment 2
Xenopus tadpoles were exposed 0, 0.1, 0.5, 1, 5, and 10 ppm DBP between 21 and 54 days of life when sexual differentiation and metamorphosis occur. The effects on reproductive development and spermatogenesis were evaluated at 33 weeks of age. Four to 6 percent of DBP-treated frogs had only one testis, and 2 to 4 percent had retained oviducts. In all DBP-treated groups, seminiferous tubule diameters and the number of germ cell nests per tubule was lower and the number of tubules with no germ cell nests was higher (p < 0.05). The percent of secondary spermatogonial nests significantly decreased (p < 0.05) in the 1.0, 5.0, and 10.0 ppm groups. In addition, dysgenetic tubules and degenerating or hypoplastic germ cell nests were observed in DBP-treated frogs. Collectively, these observations indicate that DBP at environmentally relevant concentrations has the potential to cause irreversible damage to amphibian populations by affecting survival, development, growth, and spermatogenesis.
Thus, one of the major accomplishments of the studies completed this year has been the finding that exposure of X. laevis to DBP at concentrations as low as 0.1 ppm inhibits growth of tadpoles. The LC50 and EC50 were found to be 14.5 ppm and 0.98 ppm, respectively.
Future Activities:
We will perform seminal, hormonal, and histopathological analyses of all rabbit studies, as well as the histopathological evaluations of the third experiment in frog studies during the coming year.
Journal Articles:
No journal articles submitted with this report: View all 16 publications for this projectSupplemental Keywords:
abnormal male sexual differentiation, testicular dysgenesis, animal model, animal studies, children's environmental health, dermal exposure, exposure assessment, exposure pathways, fertility, frog deformities, human exposure, human health risk, phtalates, reproductive development, reproductive effects, reproductive function, reproductive health, risk assessment,, RFA, Scientific Discipline, Health, Toxicology, Health Risk Assessment, Chemistry, Risk Assessments, Disease & Cumulative Effects, Children's Health, Ecological Risk Assessment, Biology, risk assessment, frog deformities, dermal contact, animal model, phtalates, children, fertility, Human Health Risk Assessment, reproductive development, human exposure, children's environmental health, exposure pathways, animal studies, reproductive health, reproductive function, diopathic infertility, exposure assessment, human health riskProgress and Final Reports:
Original AbstractThe perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.