FROG

Aim of the study

The aim of the study is to examine if pesticides can affect development (metamorphosis, sexual differentiation and growth) and endocrine function in amphibians and if pesticides through these modes of action can be contributing factors to amphibian decline. In order to study this, an amphibian model, applying Rana temporaria as a model species, was established.

The project has been financed by the Norwegian Research Council.

Participants:

<>Professor Bjørn Munro Jenssen
Post doc Angels Leiva-Presa
Professor Rolf A. Andersen
Associate professor Augustine Arukwe

Summary of the project
The effects of environmental contamination on amphibians are of particular concern because there are reports of declining populations in most parts of the world. During the last decade there has been increased focus on the role of persistent organic pollutants as endocrine disrupters. To study the effects of three different pesticides (p,p’-DDE, one of the most persistent metabolites of the pesticide DDT, Fenitrothion and Permethrin) on endocrine systems of adult amphibians, we subcutaneously exposed adult European common frogs (Rana temporaria) to 0, 0.01, 0.1, 1 and 10 mg pesticide/kg body mass and studied the effect of a 14 days-exposure. The study showed that of the three examined pesticides, p,p’-DDE was the only compound which had significant effects on the examined endocrine variables in the adult European common frogs. Permethrin and Fenitrothion did not have any major significant effects, and therefore seem to be more environmentally safe with regards to endocrine disruptive effects in adult male common frogs. The project has documented that the hepatic Vitamin A homeostasis was affected by exposure to p,p’-DDE, possibly by decreasing CYP26 expression and thus levels of this enzyme which is involved in the metabolism of retinoids. The project also documented that p,p-DDE doses induced changes of TRα and TRβ mRNA expression in the brain, testes, kidney and liver. Furthermore, the project indicates that antioxidant stress functions related to SOD activity are affected by p,p’-DDE, while CAT is not affected by by p,p’-DDE exposure. In gonads a decrease in MT synthesis at low doses of p,p’-DDE exposure could indicate a repression of the defence systems. The project also showed that the bone density was negatively affected following exposure to p,p’-DDE. In frogs exposed to PCB, a significantly higher variation in the estradiol-testosterone ratio in the exposed groups than in the control group may indicate that the sex-hormone homeostasis of male R. temporaria is affected by PCBs shortly after arousal from hibernation, but that the effects are subtle and that several different mechanisms are involved. The effects on the retinol homeostasis of adult male European common frogs documented in the present project, warrants the need for further studies on other wildlife species with respect to retinol related effects caused by persistent organic pollutants. There is also a need for linking the documented effects on retinoid homeostasis to ecological effects which occur in the natural environment. <> 
.

Publications from the project

Arukwe A, 2006. Organ-specific Patterns of P450arom Gene Isoforms are modulated by p,p′-DDE in Adult Male European Common Frog, Rana temporaria  Mar Environ Res 62: S215-S218 .

Arukwe A, Jenssen BM, 2005. Differential organ expression patterns of thyroid receptor isoform genes n p,p'-DDE-treated adult male common frogs, Rana temporaria. Environ Toxicol Pharmacol 20.

Leiva-Presa A, Mortensen AS, Arukwe A, Jenssen BM, 2006. Altered hepatic retinol and cyp26 levels in adult European frog (Rana temporaria) exposed to p,p'-DDE. Mar Environ Res 62: S10-S15.

Leiva-Presa A, Jenssen BM, 2006a. Effects of p,p’ DDE on retinoid homeostasis and sex hormones of adult male European common frogs (Rana temporaria). J Toxicol Environ Health in press.

Lundberg R, Leiva-Presa A, Jenssen BM, Rönn M, Hernhag C, Wejheden C, Larsson S, Örberg J, Lind PM, 2006. Effects of short-time exposure to the DDT metabolite p,p’-DDE on bone tissue in male common frog (Rana Temporaria). J Toxicol Environ Health in press.

Mikkelsen M, Jenssen BM, 2006. Polychlorinated biphenyls, sex steroid hormones and liver retinoids in adult male European common frogs (Rana temporaria).                 Chemosphere 63:707-715.

Leiva-Presa A, Asensio Herrera V, Hansen BH, Andersen RA, Jenssen BM, 2005a. Impact of the organic pollutant p,p'-DDE on heavy metal detoxification systems of adult frogs Rana temporaria. In: International Conference on Heavy Metals in the Environment (ICHMET). Rio de Janeiro; 5.


Presentations

Leiva-Presa A, Jenssen BM, 2006b. Endocrine effects of pesticides in the European common frog, Rana temporaria. In: Society of Environmental Toxicology and Chemistry, SETAC Europe 16th Annual Meeting. den Hague, The Netherlands.

Leiva-Presa A, Mortensen AS, Arukwe A, Jenssen BM, 2005c. Hepatic retinol and cyp26 levels in adult male European frog (Rana temporaria) after subcutaneous exposure to the organochlorine metabolite p,p'-DDE. In: PRIMO 13. Alessandria, Italy.