Effects of ovariectomy on parafollicular cells in the rat.

Changes in the parafollicular cells in the thyroid gland of ovariectomized rats were investigated to clarify the relationship between the secretory function of sex hormones and that of parafollicular cells. Compared with control rats, the ovariectomized rats exhibited decreases in 1) the number of parafollicular cells in the thyroid glands, 2) the number of secretory granules in the parafollicular cells, and 3) the area occupied by the Golgi complex. These results suggest that the lack of estrogen caused by ovariectomy reduces the synthesis and release of calcitonin in parafollicular cells, which may be one of the causes of osteoporosis.