Hypothalamic–pituitary–thyroid axis Hypothalamic–pituitary–thyroid axis The hypothalamic–pituitary–thyroid axis (HPT axis for short, a.k.a. thyroid homeostasis or thyrotropic feedback control) is part of the neuroendocrine system responsible for the regulation of metabolism. As its name suggests, it depends upon the hypothalamus, the pituitary gland, and the thyroid gland. The hypothalamus senses low circulating levels of thyroid hormone (Triiodothyronine (T3) and Thyroxine (T4)) and responds by releasing thyrotropin-releasing hormone (TRH). The TRH stimulates the anterior pituitary to produce thyroid-stimulating hormone (TSH). The TSH, in turn, stimulates the thyroid to produce thyroid hormone until levels in the blood return to normal. Thyroid hormone exerts negative feedback
Combined rapid anterior pituitary evaluation panel Combined rapid anterior pituitary evaluation panel A triple bolus test or a dynamic pituitary function test is a medical diagnostic procedure used to assess a patient's pituitary function. A triple bolus test is usually ordered and interpreted by endocrinologists. In rare cases, it has been associated with pituitary apoplexy. Three hormones (usually synthetic analogues) are injected as a bolus into the patient's vein to stimulate the anterior pituitary gland: The gland's response is assessed by measuring the rise in cortisol and growth hormone (GH) in response to the hypoglycaemia caused by insulin, rises in prolactin and thyroid-stimulating hormone (TSH) caused