Feeding of phytosterols reduced testosterone production by modulating GnRH and GnIH expression in the brain and testes of male Japanese quail (Coturnix coturnix japonica)
Phytosterols (PS), or plant sterols used as cholesterol-lowering agents, have been shown to act as endocrine-disrupting chemicals in some laboratory animals. Moreover, dietary PS efficiently pass through the blood-brain barrier and accumulate in brain cell membranes. We asked whether the accumulation of PS affects reproduction through the hypothalamic-pituitary-gonadal axis. Thirty male quail chicks were randomly divided into 3 groups (control, 80 mg/kg BW, and 800 mg/kg BW), and daily single doses of PS or vehicle were gavaged into the crop sac from 15 to 100 d of age. At the end of the entire period, half of each group was injected intramuscularly with either 10 μg of chicken gonadotropin-releasing hormone 1 (cGnRH-1) or phosphate-buffered saline solution (PBS) as the vehicle. Blood was collected before and 30 min after cGnRH-1 challenge by jugular venipuncture and decapitation, respectively. The results indicated that testosterone concentrations were low (P < 0.05) before (800 mg/kg BW) and after GnRH challenge in PS-treated quails compared with controls (P < 0.001). However, luteinizing hormone (LH) levels were not different among the groups before cGnRH-1 challenge. In addition, PS-gavaged animals failed to manifest increased LH levels after cGnRH-1 injection (P < 0.01). The same trends were observed in pituitary LH levels at 800 mg/kg BW PS after cGnRH-1 injection (P < 0.05). Real-time PCR results revealed that PS (800 mg/kg BW) feeding reduced expression of GnRH-1 in the brain and testes compared to controls. However, gonadotropin-inhibitory hormone (GnIH) expression was significantly elevated before and after GnRH-1 challenges in the brain and testes. Collectively, these results suggest that brain-mediated effects of PS on gonadal function occurs via the induction of GnIH gene expression, and these indirect effects are less potent than direct effects.