Hypothalamic-pituitary-ovarian Axis in Thyroid Dysfunction

It has been established that thyroid dysfunction causes impairment of reproductive function. However, laboratory and human studies that associated this with female reproductive hormones are conflicting and data reporting the effects of thyroid dysfunction on reproductive organs are insufficient.

This study investigated the effect of experimental hypothyroidism and hyperthyroidism on hypothalamic-pituitary-ovarian axis and reproductive organs morphometry and histology in female rats.

Laboratory animals were randomized into one of the three groups: control, carbimazole-induced hypothyroidism and levothyroxine-induced hyperthyroidism.

Organ morphometry and serum follicle stimulating hormone (FSH) were statistically comparable across all groups. Serum progesterone increased in hypothyroid rats but was reduced in hyperthyroid rats when compared with the control (p < 0.05). Body weight gain, serum luteinizing hormone and oestradiol were significantly reduced in both hypothyroid and hyperthyroid states when compared to the control. Hypothyroidism and hyperthyroidism also led to alterations in organ cytoarchitecture.

Findings from this study suggest that impairment of reproductive function associated with thyroid dysfunction is attendant with derangement of hormonal milieu and alteration in reproductive organs cytoarchitecture. Luteinizing hormone and oestradiol are implicated.