Diana M. Papoulias Jeffrey J. Whyte Donald E. Tillitt Catherine A. Richter 2016 <p><span>Atrazine has been implicated in reproductive dysfunction of exposed organisms, and previous studies documented decreased egg production in Japanese medaka (</span><i>Oryzias latipes</i><span>) and fathead minnows (</span><i>Pimephales promelas</i><span>) during 30-d to 38-d exposures to 0.5 µg/L, 5 µg/L, and 50 µg/L atrazine. The authors evaluated possible mechanisms underlying the reduction in egg production. Gene expression in steroidogenesis pathways and the hypothalamus–pituitary–gonad axis of male and female fish was measured. Atrazine did not significantly induce gonad aromatase (</span><i>cyp19a1a</i><span>) expression. An atrazine-induced shift in the number of females in an active reproductive state was observed. Expression of the egg maturation genes vitellogenin 1 (</span><i>vtg1</i><span>) and zona pellucida glycoprotein 3.1 (</span><i>zp3.1</i><span>) in medaka females was correlated and had a bimodal distribution. In both species, females with low </span><i>vtg1</i><span> or </span><i>zp3.1</i><span> expression also had low expression of steroidogenesis genes in the gonad, estrogen receptor in the liver, and gonadotropins in the brain. In the medaka, the number of females per tank that had high expression of </span><i>zp3.1</i><span> was significantly correlated with egg production per tank. The number of medaka females with low expression of </span><i>zp3.1</i><span> increased significantly with atrazine exposure. Thus, the decline in egg production observed in response to atrazine exposure may be the result of a coordinated downregulation of genes required for reproduction in a subset of females.</span></p> application/pdf 10.1002/etc.3376 en Society of Environmental Toxicology and Chemistry Evaluation of potential mechanisms of atrazine-induced reproductive impairment in fathead minnow (<i>Pimephales promelas</i>) and Japanese medaka (<i>Oryzias latipes</i>) article