Therefore, we evaluated the ultrastructure of the thyroid gland, the hepatic Dio1 expression, and circulating thyroid hormone levels in pregnant rats with preeclampsia induced by NG-nitro-L-arginine-methyl ester (L-NAME), to provide reliable experimental evidences for revealing the underlying mechanisms of hypothyroidism in preeclampsia; we further observed whether these changes were improved after administration of amlodipine besylate, a commonly used antihypertensive agent. Here, DIO1 is linked to hypothyroidism.