AVALIAÇÃO DOS EFEITOS DA EXPOSIÇÃO PERINATAL À BAIXAS DOSES DE BISFENOL A SOBRE O EIXO HIPOTALÂMICO-HIPOFISÁRIO-TESTICULAR DA PROLE ADULTA DE RATOS

Abstract

The hypothalamic-pituitary-testicular axis (HPT) establishes the relationship between the central nervous system and the testis, playing a key role in the production of steroid hormones and in the male reproduction. Bisphenol A (BPA) is a synthetic endocrine chemical disrupter of high prevalence in the environment that may influence the function of the HPT axis in adult rats. The objective of this study was to evaluate whether exposure to BPA at doses below the reproductive NOAEL, during hypothalamic sexual differentiation window, causes changes in the regulation of HPT axis. Female Wistar rats were mated and treated with BPA from the gestational day 18 until postnatal day (PND) 5. BPA was diluted in corn oil and administered by subcutaneous injection once a day only to mothers, in doses corresponding to zero, 0.5 or 5 mg of BPA / kg of body weight. In PND5 litters were standardized in eight pups per dam and the ratio was maintained until weaning (PND21). Body growth was accompanied through weekly weighing, from weaning until PND90. From the PND30 was initiated the evaluation of puberty progression. In PND90, the offspring was euthanized and blood, hypothalamus, pituitary and testis were collected and stored at -80 °C. The testis, epididymis and seminal vesicles were weighed. The mRNA expression was evaluated by quantitative PCR real time (RT-qPCR). In hypothalamus, was performed the evaluation of the following genes: gonadotropin releasing hormone (Gnrh1), estradiol alpha receptor (Esr1), estradiol receptor beta (Esr2) and androgen receptor (Ar). In pituitary, releasing hormone receptor gonadotropin (Gnrhr), luteinizing hormone (Lhb), follicle stimulating hormone (Fshb), Esr1, Esr2 mRNA expression was analyzed. Finally, in the testis were evaluated luteinizing hormone receptor (Lhcgr), luteinizing hormone receptor (Fshr) and the Inhibin beta (Inhbb) mRNA expression. Serum testosterone and estradiol were assessed by electrochemoluminescence immunoassay and serum LH and FSH were assessed by chemiluminescence. Data were analyzed by MANOVA for repeated measures (evaluation of growth), Kruskal-Wallis followed by Dunn posthoc test (age at puberty and testosterone), and one-way ANOVA followed by Tukey HSD posthoc test for all other comparisons with the resources of the software Statistica 7.0, Statsoft Inc. Statistical differences were considered when p <0.05. The perinatal exposure to BPA did not change the body growth, but delayed the age and increased the weight at puberty in animals of both treated groups. The amount of seminal vesicle fluid increased in animals treated with the higher dose of BPA. The epididymis weight was reduced in the same group. The hypothalamic expression of Gnrh mRNA and Esr2 increased in animals of both treated groups. In pituitary, Fshb and Ar mRNA expression were increased in the group treated with the lowest dose of BPA, while Esr1 mRNA expression was only augmented in the highest dose group. In testis, there was an increase in the transcript expression of Fshr and Inhbb only in the group treated with the lower dose of BPA. Serum testosterone and LH levels were increased in the group treated the higher dose of BPA. These results firstly demonstrate that perinatal exposure to low doses of BPA, during critical period of hypothalamic sexual differentiation, modifies the activity of the HPT axis of the offspring with consequences in adult life of rats.