Effects of acute exposure to microcystins on hypothalamic-pituitary-adrenal (HPA), -gonad (HPG) and -thyroid (HPT) axes of female rats.

Microcystins (MCs) are common, well-known cyanobacterial toxins that can affect health of humans. Recently, it has been reported that MCs affect endocrine functions. In the present study, for the first time, histopathology, concentrations of hormones and transcription of genes along the hypothalamic-pituitary-adrenal (HPA), hypothalamic-pituitary-gonad (HPG) and hypothalamic-pituitary-thyroid (HPT) axes were examined in rats exposed to microcystin-LR (MC-LR). Female, Sprague-Dawley (SD) rats were exposed acutely to MC-LR by a single intraperitoneal (i.p.) injection at doses of 0.5, 0.75, or 1 median lethal dose (LD), i.e. 36.5, 54.75, or 73 μg MC-LR/kg body mass (bm) then euthanized 24 hours after exposure. Acute exposure to MC-LR significantly increased relative mass of adrenal in a dose-dependent manner, but relative mass of hypothalamus, pituitary, ovary and thyroid were not significantly different from respective mass in controls. However, damage to all these tissues was observed by histology. Along the HPA axis, lesser concentrations of corticotropin-releasing hormone (CRH), adrenocorticotropic hormone (ACTH) and corticosterone (CORT) were observed in blood serum of exposed individuals, relative to controls. For the HPG axis, concentrations of gonadotropin-releasing hormone (GnRH) and estradiol (E2) were significantly less in rats treated with MC-LR, but greater concentrations of luteinizing hormone (LH), follicle-stimulating hormone (FSH) and testosterone (T) were observed. Along the HPT axis, MC-LR caused greater concentrations of thyroid-stimulating hormone (TSH), but lesser concentrations of thyrotropin-releasing hormone (TRH), free tetra-iodothyronine (fT4) and tri-iodothyronine (fT3). Significant positive/negative correlations of concentrations of hormones were observed among the HPA, HPG and HPT axes. In addition, profiles of transcription of genes for synthesis of hormones along the endocrine axes and nuclear hormone receptors in adrenal, ovary and thyroid were significantly altered. Therefore, these results suggested that MC-LR affected HPA, HPG and HPT axes and exerted endocrine-disrupting effects. Effects of MC-LR on crosstalk among these three axes need further studies.