In Vivo Investigation of the Effects of Nonylphenol on the Pituitary–Adrenal Axis and Pineal Gland in Male Rats

The pineal gland secretes melatonin, which regulates various physiological processes; damage to this gland disrupts these functions. This study aimed to investigate the effect of nonylphenol on the pineal gland and the pituitary–adrenal axis, which is associated with this system. The study was initiated using Wistar albino male rats on their postnatal 21st day, a critical developmental stage for endocrine regulation. Nonylphenol was administered via oral gavage at doses of 5, 25 and 125 mg/kg/day, while bisphenol-A was given at 50 mg/kg/day as a positive control. At the end of the treatment period, liver, kidney, pituitary, pineal and adrenal tissues were examined histopathologically. Hormone levels were analysed in serum samples. Significant changes in adrenocorticotropic hormone, melatonin and aldosterone levels were detected in hormone analyses. In contrast, no differences in corticosterone and glucose levels were detected. Histopathological findings showed structural changes in tissues. The effects of nonylphenol on the pituitary–adrenal axis and melatonin vary depending on the experimental protocols employed. However, it is clear that nonylphenol and bisphenol A have negative effects on the pituitary–adrenal axis, pineal gland, liver and kidney. In conclusion, future research should focus on elucidating the molecular mechanisms underlying these effects and developing environmentally friendly strategies to eliminate nonylphenol and bisphenol-A contamination.