The Phytoestrogen β-Sitosterol Alters the Reproductive Endocrine Status of Goldfish

There is a growing awareness that chemicals in the environment may function as hormone mimics and affect endocrine function in wildlife. In this study, the effects of beta-sitosterol, a phytoestrogen present in high concentration in bleached kraft pulp mill effluent (BKME), on reproductive fitness of goldfish were investigated. Plasma reproductive hormone levels were measured in male and female goldfish on Day 4 following two intraperitoneal injections of beta-sitosterol or an oxidized sitosterol preparation. In some experiments, plasma hormone levels were also measured after fish were injected with Ovaprim, which contains a superactive analog of salmon GnRH and the dopamine receptor antagonist domperidone and leads to increased secretion of gonadotropin (GtH)-II (LH-type GtH). Plasma testosterone (T) and 11-ketotestosterone levels in males and T and 17 beta-estradiol levels in females were significantly decreased in beta-sitosterol-treated fish on Day 4 and 24 hr after an injection of Ovaprim. Plasma GtH-II levels were elevated in male fish treated with beta-sitosterol on Day 4 and further increased in response to Ovaprim, suggesting that reduced plasma steroid levels were not due to effects on pituitary function. In other studies, testes pieces from beta-sitosterol-treated goldfish produced reduced levels of T and pregnenolone in vitro both basally and in response to the GtH-II agonist human chorionic gonadotropin (hCG) when compared to the testes from control fish. Basal and hCG-stimulated pregnenolone and hCG-stimulated T were reduced in follicles from beta-sitosterol-treated fish; however, basal T production was not different from controls. These results suggest that beta-sitosterol reduces the gonadal steroid biosynthetic capacity through effects on cholesterol availability or the activity of the side chain cleavage enzyme P450SCC. These findings raise the possibility that beta-sitosterol could be a contributing factor to the reproductive dysfunction observed in fish exposed to BKME.