Permanent alterations in the hypothalamic-pituitary-thyroid axis in the rat following phenytoin exposure in utero.

Phenytoin exposure in utero results in permanent alterations of the hypothalamic-pituitary-thyroid axis in the rat. The DPH exposed animals have decreased weight gain, thyroxine and triiodothyronine concentrations. In addition, they have blunted thyroid-stimulating hormone responses to thyrotropin-releasing hormone, propylthiouracil challenge or thyroidectomy. The diminished pituitary response in these animals is similar to that reported in neonatal thyrotoxicosis in the rat. This may be due, in part, to structural similarities between phenytoin and the thyroid hormone.