GALANIN GENE-EXPRESSION IN RADIOTHYROIDECTOMY-INDUCED THYROTROPH ADENOMAS

Galanin gene expression is markedly increased in the anterior pituitar y glands of estrogen-treated rats (lactotroph hyperplasia) as well as human growth hormone-releasing hormone transgenic mice (somatotroph hy perplasia). The objective of this study was to examine galanin in a mo use model of thyrotroph adenoma formation. Male mice were radiothyroid ectomized by use of iodine-131 (I-131), and galanin peptide levels wer e assessed in the hypothalamic-pituitary axis. Immunoreactive galanin concentrations in the anterior pituitaries of I-131-treated mice were decreased 80% at 3, 6, 9, and 12 mo after radiothyroidectomy. Galanin peptide levels in the hypothalamus were decreased 20-25% at these time s. Treatment with either estradiol or 3,3',5-triiodo-L-thyronine incre ased galanin peptide concentrations in the anterior pituitaries of I-1 31-treated mice, but neither treatment restored galanin concentrations . Galanin mRNA levels were decreased >80% 1 yr after radiothyroidectom y. We conclude that, unlike animal models of lactotroph and somatotrop h hyperplasia, galanin gene expression is suppressed throughout the de velopment of thyrotroph adenomas, suggesting that galanin does not hav e a stimulatory role in the proliferation of thyrotrophs. Moreover, th ese data show that thyroid hormones are important positive regulators of galanin gene expression in the mouse and that estrogen may stimulat e galanin gene expression in the absence of thyroid hormones.