Evaluation of potential mechanisms of atrazine‐induced reproductive impairment in fathead minnow (Pimephales promelas) and Japanese medaka (Oryzias latipes)

Abstract

Atrazine has been implicated in reproductive dysfunction of exposed organisms, and previous studies documented decreased egg production in Japanese medaka (Oryzias latipes) and fathead minnows (Pimephales promelas) 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 (cyp19a1a) 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 (vtg1) and zona pellucida glycoprotein 3.1 (zp3.1) in medaka females was correlated and had a bimodal distribution. In both species, females with low vtg1 or zp3.1 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 zp3.1 was significantly correlated with egg production per tank. The number of medaka females with low expression of zp3.1 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. Environ Toxicol Chem 2016;35:2230-2238. Published 2016 Wiley Periodicals Inc. on behalf of SETAC. This article is a US Government work and, as such, is in the public domain in the United States of America.

Comparing the effects of atrazine and an environmentally relevant mixture on estrogen‐responsive gene expression in the northern leopard frog and the fathead minnow

“…b Only one sample analyzed. However, the study by Richter et al [23] did not observe the same alterations in hepatic expression of ERa as the present study. Samples were taken from stock replacement water prepared for both fish and frogs on days 0 and 6 (n ¼ 2).…”

“…Values represent the mean (AE standard error of the mean). Following a 30-d exposure to atrazine at the same nominal concentrations as the present study, female fathead minnows experienced down-regulations of genes involved in gonadal steroidogenesis and luteinizing hormone signaling that were also associated with reduced egg production [23]. n.d. ¼ not detected.…”

“…n.d. ¼ not detected. Fish in the present study were maintained under single-sex conditions, whereas Richter et al [23] maintained fish under mixed-sex conditions so that they could assess the impacts of atrazine on egg production over the course of exposure. Values represent the mean (AE standard error of the mean).…”

“…Controls for both the fish and frog exposures consisted of a 0.0025% acetone solvent control, a concentration that is below the threshold for response from either fathead minnows [21,23] or northern leopard frogs [24]. For the atrazine dose-response study, atrazine stock solutions were prepared in pure acetone for subsequent preparation of treatment solutions over the course of the 7-d exposure.…”

Fish short‐term reproduction assay with atrazine and the Japanese medaka (Oryzias latipes)

“…Although there was a statistically significant increase in expression of vtg-II in males exposed to 5.5 mg/L, the relatively large degree of variability within the treatment group (fold change of 6.9 AE 3.8), particularly in 2 fish in replicate D demonstrating fold changes of 16.2 and 25.51 versus 0.31 to 7.10 for the other 8 male fish in this treatment replicate, and the lack of concurrent effects on the other measured reproductive endpoints suggested that the upregulation of the gene did not translate to significant effects in reproductive fitness. Richter et al [32] also reported a lack of dose-dependent expression of hepatic vitellogenin (vtg-I) in medaka exposed to up to 50 mg/L for 14 or 38 d and noted that this was in agreement with other characterizations of effects of atrazine in fish and amphibians. Likewise, Span o et al [27] reported that atrazine at concentrations up to 1000 mg/L had no effect on plasma vitellogenin levels in goldfish, and the review by Van Der Kraak et al [9] concluded that the weight of evidence suggested that atrazine exposure had no effects on vitellogenin in fish.…”