Effect of conjugated equine estrogens and tamoxifen administration on thyroid gland histomorphology of the rat

Abstract

OBJECTIVE: The aim of this study was to evaluate the action of the conjugated equine estrogens and tamoxifen on the morphology of thyroid gland in ovariectomized (OVx) rats. METHODS: Conjugated equine estrogens (CEE), clinically used as estrogen therapy, is a complex formulation containing multiple estrogens that decrease menopausal symptoms. Thirty ovariectomized rats were randomly divided into 3 treatment groups: GI, vehicle (propylene glycol); GII, CEE 200 µg/kg per day; and GIII, tamoxifen 1 mg/kg per day. Another group of 10 rats with intact ovaries (GIV) was included, treated with the vehicle, and sacrificed during estrous. All animals were treated by gavage for 50 days, after which they were sacrificed. Blood samples were collected, and the thyroid was removed for morphological analysis and PCNA evaluation through immunohistochemical study. RESULTS: The thyroid follicular cell height was increased in animals treated with CEE (14.90 ± 0.20 µm), with TAM (14.90 ± 0.10 µm), and in rats with intact ovaries (15.10 ± 0.50 µm) in comparison to that of the vehicle group (9.90 ± 0.20 µm) (P < 0.001). The follicular area was larger in the CEE (2,225 ± 51 µm²) and TAM (2,127 ± 67 µm²) groups compared to that of the vehicle group (5,016 ± 53 µm²). The levels of T4 and T3 in rats treated with CEE, with Tamoxifen and in rats with intact ovaries, were higher than those those in the vehicle group (P < 0.001). The PCNA index in the vehicle group was lower than in other groups. CONCLUSION: Our data suggest that estrogen and tamoxifen administration has a proliferative effect on the thyroid.