Thyroidectomy induces neurofilament expression in adenohypophyses of rats.

We studied the effect of thyroidectomy on neurofilament expression in adenohypophyses of rats. The question of whether thyroxine (T4) administration can reduce this effect was also investigated. Rats were divided into: 1. Euthyroid controls, 2. Thyroidectomized 20 d (Tx 20 d), 3. Thyroidectomized 20 d with replacement of T4 (Tx 20 d + T4 20 d), 4. Thyroidectomized 40 d (Tx 40 d), 5. Thyroidectomized 40 d with replacement of T4 20 d after surgery (Tx 40 d + T4 20 d). Adenohypophyses were studied by immunohistochemistry and Western blot analysis using antibodies against neurofilament 200 kDa (NF-H) and thyroid-stimulating hormone (TSH). The number of thyrotrophs with immunoreactivity for NF-H was increased in Tx 20 d and Tx 40 d rats, whereas T4 administration protected the effect of thyroidectomy. In the thyroidectomized animals, thyrotrophs showed eccentric nuclei and the cytoplasm was full of NF-H immunoreactivity, whereas in T4 treated rats, the thyrotrophs were similar to control. Western blot analysis showed that NF-H expression increased in rats thyroidectomized for 20 and 40 d. T4 given immediately or 20 d after thyroidectomy caused no changes in NF-H expression. We conclude that thyroidectomy induces NF-H expression in adenohypophyses of rats and administration of T4 decreases this effect.