Hypothyroidism affects differentially the cell size of epithelial cells among oviductal regions of rabbits.

Oviductal regions show particular histological characteristics and functions. Tubal pathologies and hypothyroidism are related to primary and secondary infertility. The impact of hypothyroidism on the histological characteristics of oviductal regions has been scarcely studied. Our aim was to analyse the histological characteristics of oviductal regions in control and hypothyroid rabbits. Hypothyroidism was induced by oral administration of methimazole (MMI) for 30 days. For both groups, serum concentrations of thyroid and gonadal hormones were determined. Sections of oviductal regions were stained with the Masson's trichrome technique to analyse both epithelial and smooth muscle layers. The percentage of proliferative epithelial cells (anti-Ki67) in diverse oviductal regions was also quantified. Data were compared with Student t-test, Mann-Whitney U-test, or Fischer's test. In comparison with the control group, the hypothyroid group showed: (i) a low concentration of T3 and T4, but a high level of TSH; (ii) similar values of serum estradiol, progesterone and testosterone; (iii) a large size of ciliated cells in the ampulla (AMP), isthmus (IST) and utero-tubal junction (UTJ); (iv) a large size of secretory cells in the IST region; (v) a low percentage of proliferative secretory cells in the fimbria-infundibulum (FIM-INF) region; and (vi) a similar thickness of the smooth muscle layer and the cross-sectional area in the AMP and IST regions. Modifications in the size of the oviductal epithelium in hypothyroid rabbits could be related to changes in the cell metabolism that may impact on the reproductive functions achieved by oviduct.