thyrotrophs

Thyrotrophs are a population of hormone-secreting cells in the anterior pituitary (adenohypophysis) responsible for the production and release of thyroid-stimulating hormone (TSH). They are a relatively small group within the pituitary and arise from Rathke’s pouch, the embryonic precursor of the adenohypophysis.

TSH release from thyrotrophs is regulated by hypothalamic input and negative feedback. Thyrotropin-releasing hormone (TRH) from the hypothalamus stimulates TSH secretion, while circulating thyroid hormones (primarily T3 and T4) inhibit TSH release at both the pituitary and hypothalamic levels. Somatostatin can exert inhibitory effects on TSH secretion in some contexts. TSH secretion exhibits pulsatility and is influenced by circadian factors.

The primary action of TSH is to stimulate the thyroid gland. It binds to the TSH receptor on thyroid follicular cells, activating the adenylate cyclase–cAMP signaling pathway. This promotes growth of the thyroid, iodide uptake, and the synthesis and release of thyroid hormones (thyroxine, T4, and triiodothyronine, T3). TSH also upregulates enzymes involved in thyroid hormone synthesis, such as thyroid peroxidase, and enhances thyroglobulin production.

Molecular and histological markers distinguish thyrotrophs. They express the beta subunit of TSH, which confers hormone specificity, whereas the alpha subunit is shared with other glycoprotein hormones (LH, FSH, and hCG). Immunohistochemical detection of TSH beta helps identify thyrotrophs in tissue.

Clinically, TSH-secreting pituitary adenomas (thyrotropinomas) produce inappropriately high TSH with elevated thyroid hormones, leading to hyperthyroidism. More commonly, thyroid function is suppressed in primary thyroid disease, highlighting the role of thyrotrophs in central regulation of thyroid activity.