Effect of progestin on thyroid function in female Wistar rats.

Introduction: To characterize the influence of female-specific hormones on women's thyroid function, the study investigated the influence of extra progestin from oral contraceptives on inducing thyroid dysfunction.

Methods: Sixty female Wistar rats were divided into six groups based on levonorgestrel or desogestrel administration as the main active agents: control, low (0.0039 mg*20-fold), medium (0.0039 mg*100-fold), high (0.0318 mg*100-fold) levonorgestrel (pure product); and low (0.0083 mg*20-fold) and high (0.0083 mg*100-fold) desogestrel (pure product). Progestin was administered by gavage every 4 days for 1 month. Statistical analysis was performed using one-way analysis of variance and the Kruskal-Wallis test.

Results: Following levonorgestrel gavage, serum free T and thyroidstimulating hormone levels were significantly lower in the experimental group than that in the control group (=0.013 and 0.043). After desogestrel gavage, the serum free T and free T levels were lower in the experimental group than that in the control group (=0.019 and 0.030). Thyroid hormone antibody concentrations were lower in rats administered levonorgestrel and desogestrel than that in control rats. Moreover, exposure to progestin upregulated the expression of the thyroid-stimulating hormone receptor and sodium iodide symporter in thyroid.

Discussion: Progestin stimulation enhanced the proliferation of follicular epithelial cells in rat thyroid tissues. Progestin exposure could cause thyroid dysfunction by upregulating the transcription of thyroid-stimulating hormone receptor and sodium iodide symporter in thyroid, thus inducing pathomorphological changes in rats' thyroid.