Gonadotropin profile in experimentally induced hypothyroid and hyperthyroid cyclic female rats

Abstract

The current study examined the association of thyroid disorders with reproductive dysfunction by determining its effect on gonadotropin secretion in cyclic female rats. Sixty cyclic females were assigned to three groups (20 each) and supplemented, for 30 days plus two consequent estrous cycles, with drinking water (control), methimazole in drinking water (0.02% w/v) (hypothyroid group), and thyroxine in drinking water (0.002% w/v) and gastric gavage of 200 μg/kg body weight (hyperthyroid group). At late proestrus, ten females from each group (for each cycle) were anesthetized and dissected. Blood samples were obtained to assess thyroid-stimulating hormone, free and total triiodothyronine, free and total thyroxin, follicle-stimulating hormone, luteinizing hormone, and prolactin concentrations. Ovarian and pituitary tissue samples were obtained for molecular analysis of ovarian thyroid receptor genes and pituitary TSH, FSHβ, and LHβ genes. In comparison with control, the Hypo group revealed increased serum concentrations of TSH and PRL and the expression levels of pituitary TSH and ovarian TRsTRs genes and significant decrease of FT3, TT3, FT4, TT4, FSH, and LHLH concentrations and the expression levels of pituitary FSHβ and LHβ genes. In contrast, the Hyper group showed increased serum FT3, TT3, FT4, TT4, and LHLH concentrations and the expression levels of pituitary LHβ and ovarian TRsTRs genes and decreased serum TSH FSH and PRL concentrations and pituitary FSHβ and TSH gene expression levels. It is concluded that thyroid dysfunction is associated with altered serum gonadotropin secretion and reproductive failure.