Goiter formation following prostaglandin administration in rats.

Prostaglandins (PGE1 and PGE2) induced a hyperplastic microfollicular goiter with a high radioiodine (131I) thyroid uptake, increased endocytosis, a heavy autoradiographic (125I) reaction, and a moderate increase of thyroid hormones (T4, T3), thyroxine-binding globulin (TGB), and thyrotropin (TSH) concentrations in adult rats. Ultrastructurally, both prostaglandins (E1 and E2) markedly stimulated the thyroid cell activity and increased the number of pseudopodia, the size of colloid and dense granule populations, and the number of polysomes. Conversely, a hypofunction of thyroid glands with low radioiodine (131I) thyroid uptake, a decreased autoradiographic (125I) reaction, and a moderate decrease in T4, T3, TGB, and TSH concentrations were observed following prostaglandin F 2alpha. Ultrastructurally, a decrease in size of the colloid and dense granule population and the number of degenerative mitochondria occurred infollicular cells. An intense hyperplasia of parafollicular (C) cells, with abundant population of characteristic dense granules, could be seen in PGF 2alpha-treated rats. A marked decrease of radioiodine (131I) uptake, endocytosis, and autoradiographic (125I) reaction and a sharp decline in T4, T3, and TBG were observed in hypophysectomized and chronically prostaglandin-treated rats. Light and electron microscopy revealed signs of an advanced thyroid hypofunction with flat cuboidal cells, reduced microvilli, scarce endoplasmic reticulum, and few dense droplets. The present findings demonstrate that the chronic administration of prostaglandins exerts significant effects of thyroid gland and goiter formation (goitrogenesis), radioiodine metabolism, and hormone synthesis, and that these effects are mediated by TSH secretion.