In Vitro Testing of the Insecticide Reldan 22 on Swine Oocyte Maturation

Chlorpyrifos (Reldan 22) is an widely used insecticide for the control of insect pests in agricultureand in residential areas. It is classified as moderately toxic by the United States Environmental Protection Agency and has been quantified in human biological fluids. Given that the use of porcine and bovine models for testing chemicals has increased recently we designed an experiment to test the toxicity of several Chlorpyrifos concentrations and investigate its effects on maturation of swine oocytes. Swine oocytes from ovaries harvested in a commercial slaughterhouse were cultured for 44-45h in M199 supplemented with the following Reldan 22 concentrations: 0.1, 0.5, 1 or 2 µg/ml. Cumulus oophorous expansion was assessed and oocytes were denuded and stained with 1 µg/ml fluorescein diacetate to estimate viability. Afterwards, oocytes were fixed in a 60% methanol/DPBS solution and stained with 50 µg/ml propidium iodide to observe the DNA stage. Differences were analysed by the analysis of variance and interpreted using the Tuckey test. Our research shows that the insecticide Reldan 22® stimulated cumulus expansion to an extent but reduced oocyte viability which was accompanied by an increase in the number of immature oocytes and a decrease in the percentages of gametes that resumed meiosis. This leads us conclude that its presence in the oocyte environment is toxic for development at concentrations 0.5, 1 and 2 µg/ml.