In a negative feedback mechanism controlling thyroid hormone secretion which is the nonregulatory hormone?

In a negative feedback mechanism controlling thyroid hormone secretion, the nonregulatory hormone is typically thyroxine (T4). While T4 and triiodothyronine (T3) are the main hormones produced by the thyroid gland, their levels regulate the secretion of thyroid-stimulating hormone (TSH) from the pituitary gland and thyrotropin-releasing hormone (TRH) from the hypothalamus. When T4 levels rise, they inhibit the release of TRH and TSH, thus regulating their own production through negative feedback.