Thyroid Hormone Action on ACTH Secretion

Summary

Thyroid hormone effects on pituitary ACTH have not been well established. Adult male Sprague-Dawley rats were rendered hypo- and hyperthyroid while undergoing treatment with 6-Propylthiouracil (PTU) and L-Thyroxine (T₄). At the time of decapitation, plasma values for T₄ (μg/100 ml) were 3.9 ± 0.4 in the control, 17.3 ± 2.2 in the T₄ and < 2 in the PTU treated group; plasma T₃ and TSH confirmed hyper- and hypothyroidism in the T₄ and PTU treated groups respectively. Plasma immunoassayable ACTH and corticosterone were significantly increased in hyperthyroid and decreased in the PTU treated animals. Pituitaries were removed and incubated in DMEM. After 3 h incubation, ACTH content and secretion to the medium were significantly lower in the PTU group. As expected, pituitary TSH content and secretion were decreased in the T₄ treated animals. These data indicate that thyroid hormones influence pituitary-adrenal function by increasing ACTH secretion and consequently corticosterone production.

Key-Words

ACTH - Corticosterone - Thyroid Hormones - TSH