Nonylphenol affects gonadotropin levels in the pituitary gland and plasma of female rainbow trout

Female rainbow trout (Oncorhynchus mykiss) were exposed to 4-nonylphenol IN P) at (mean measured) concentrations of 0.7, 8.3, and 85.6 mug/L, for 18 we eks, during early ovarian development. Fish were sampled sublethally every six weeks, and terminal samples were taken at 18 weeks. NP induced an estro genic effect (the synthesis of vitellogenin) at concentrations of 8.3 and 8 5.6 mug/L. An effect on gonadotropin synthesis and secretion was also obser ved. Plasma follicle stimulating hormone (FSH) levels and FSH gene expressi on in the pituitary were the most sensitive endpoints assessed, being reduc ed at the lowest dose employed (0.7 mu gNP/L). Pituitary gland luteinizing hormone (LH) content was significantly lower in fish exposed to 85.6 mu gNP /L, and LH gene expression was suppressed in fish exposed to 8.3 and 85.6 m u gNP/L. In contrast, plasma LH concentration increased in these fish, but by a very minor absolute amount, and returned to control levels by the fina l sampling time. Gonadal development ceased in the fish exposed to 85.6 mu gNP/L, and steroidogenesis in these fish was also markedly inhibited. Altho ugh the mechanisms underlying these responses are unknown, this study demon strates that NP has adverse effects on pituitary function that can result i n inhibition of ovarian development.