Iraqi Journal of Veterinary Sciences

Abstract

Current study was conducted to examine the association of thyroid disorders with reproductive dysfunction, by determining its effect on gonadotropins secretion in cyclic female rats. Sixty cyclic females were assigned to three groups (20 each) and drenched, for 30 days plus 2 consequent estrous cycles, with drinking water (control), methimazole in drinking water (0.02% w/v) (hypothyroid group), and thyroxin in drinking water (0.002% w/v) and gastric gavage of thyroxin (200 μg/kg bw) (hyperthyroid group). At late proestrus, 10 females from each group (for each cycle) were anesthetized, dissected, and blood samples were obtained for assessment of 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, Hypo group revealed increased serum concentrations of TSH and PRL and the expression levels of pituitary TSH and ovarian TRs genes and significant decrease of FT3, TT3, FT4, TT4, FSH, and LH concentrations and the expression levels of pituitary FSHβ and LHβ genes, whereas Hyper group showed increased serum FT3, TT3, FT4, TT4, and LH concentrations and the expression levels of pituitary LHβ and ovarian TRs 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.