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LH gene expression is stimulated, but release is inhibited in catfish. FSH gene expression and release are suppressed in trout and tilapia. GnRH and GnRH-Rs are affected

Three different fish species, pubertal male African catfish, maturing female rainbow trout and maturing male tilapia, were exposed to relevant concentrations of a "model" environmental oestrogen, 4-nonylphenol (4-NP). The present study identified several points along the brain-pituitary- gonad axis, the neuro-endocrine system that controls reproduction, which are affected by exposure to 4-NP.

In the pituitary, two hormones that control gonadal functions are secreted: follicle stimulating hormone (FSH), mainly responsible for germ cell production, and luteinizing hormone (LH) that regulates sex hormone production. Exposure to 4-NP caused in trout and tilapia a decrease in FSH production (this hormone could not be measured in catfish). This effect is probably responsible for the disruption of cogenesis and spermatogenesis. Moreover, in catfish, LH gene expression and storage was stimulated, but its release was inhibited. LH plasma levels were not always affected in the other species.

FSH and LH secretion are under control of gonadotropin releasing hormone (GnRH) via specific GnRH receptors (GnRH-Rs) on the pituitary cells. Especially, the higher but still relevant 4-NP doses caused a down regulation of the GnRH-R gene expression in catfish, which may be responsible for a disruption of the functional connection between brain and pituitary.

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