Efeitos da exposição subcrônica ao chumbo nos parâmetros reprodutivos de Astyanax bimaculatus

Abstract

Lead (Pb) is frequently found in the aquatic environment due to anthropic activities. This element has no known biological function, is highly toxic and can cause behavioral, renal, neurological and reproductive damage in animals. Studies show that Pb acts as an endocrine disruptor (EDC), however, its effects on fish gametogenesis are unclear, and more experimental studies are needed to better understand its action on reproduction. Therefore, the aim of the study was to assess the effects of sub-chronic exposure to different concentrations of Pb on reproductive physiology of the lambari Astyanax bimaculatus, ecological relevance species and bioindicator of aquatic pollution. To carry out the experiment, the fish were exposed to lead acetate for 28 days, in three concentrations (15, 50 and 100 μg/L of Pb) and the control group, without addition of the chemical. The fish were euthanized, dissected and had biometric data and biological indices obtained. Gonad, liver and blood samples were collected to use different morphological and molecular techniques. The data showed that the exposure of lambaris to different concentrations of Pb caused a significant reduction in the gonadosomatic index, diameter of vitellogenic follicles and seminiferous tubules. The morphometric analysis of the gonads showed a significant increase in the proportion of perinucleolar follicles in the 50 µg/L group, a decrease in vitellogenic follicles and an increase in follicular atresia in the 50 and 100 µg/L groups, indicating an inhibition of oocyte growth. In males, an increase in Aund and Adiff type spermatogonia was observed in the 50 and 100 µg/L groups and B type spermatogonia in the 100 µg/L group, an increase in spermatocytes in the 50 µg/L group and a drastic reduction of sperm at 50 and 100 µg/L compared to control. In our experiment 17β-estradiol (E2) increased in the 15 and 50 µg/L groups in endorsing and 15 µg/L in males, which was also observed a significant increase in 11-ketotestosterone in the 100 µg/L. Although Pb did not alter hepatic metallothionein levels in A. bimaculatus, the toxicity of 100 ug/L Pb reduced hepatic vitellogenin in females. In the ovary, estrogen (ERα and ERβ) and androgen (AR) receptors were immunolocalized in follicular and germ cells, with different intensity patterns depending on the stage of development. In the testis, an expression of ERα and ERβ was observed in spermatogonia, spermatocytes and Leydig cells, however, Sertoli cells, spermatids and spermatozoa expressed only ERα, and strong immunostaining for RA was observed in Sertoli and Leydig cells, but weaker labeling was also detected in germ cells. Comparing the groups, the highest values for ERα were observed in the 100 µg/L Pb group and for ERβ in the 15 and 100 µg/L Pb groups compared to the control group. In males, there was a significant increase in ERα in the 100 µg/L Pb group compared to the other groups. For both sexes, there was no significant difference between the levels of AR in the treated groups compared to the control. This way, this study demonstrates that even at relatively low concentrations, subchronic exposure to Pb can impair lambari reproduction, affecting the gonadosomatic index, germ cell distribution, production of sex steroids by the gonads and essential proteins for reproductive development, as well as the levels of estrogen receptors, therefore acting as a metalloestrogen.