Protirelin is the pharmaceutically available synthetic analogue of the endogenous peptide thyrotropin-releasing hormone (TRH). It is a tri-peptide tropic hormone, released by the hypothalamus, which stimulates the release of Thyroid Stimulating Hormone (TSH) and prolactin from the anterior pituitary. Although not currently available in any FDA-approved product, protirelin is a component of the TRH Test where it is used to test the response of the anterior pituitary gland in conditions such as secondary hypothyroidism and acromegaly. TRH is indicated as an adjunctive agent in the diagnostic assessment of thyroid function. As an adjunct to other diagnostic procedures, testing with TRH (protirelin) may yield useful information in patients with pituitary or hypothalamic dysfunction. TRH is indicated as an adjunct to evaluate the effectiveness of thyrotropin suppression with a particular dose of T4 in patients with nodular or diffuse goiter. A normal TSH baseline value and a minimal difference between the 30 minute and baseline response to TRH injection would indicate adequate suppression of the pituitary secretion of TSH. TRH may be used, adjunctively, for adjustment of thyroid hormone dosage given to patients with primary hypothyroidism. A normal or slightly blunted TSH response, thirty minutes following TRH injection, would indicate adequate replacement therapy. Side effects have been reported in about 50% of the patients tested with TRH. Generally, the side effects are moor, have occurred promptly, and have persisted for only a few minutes following injection. Cardiovascular reactions: Marked changes in blood pressure, including both hypertension and hypotension with or without syncope, have been reported in a small number of patients. Endocrine reaction: Breast enlargement and leakage in lactating women for up to two or three days. Other reactions: Headaches, sometimes severe, and transient amaurosis in patients with pituitary tumors. Rarely, convulsions may occur in patients with predisposing conditions, e.g., epilepsy, brain damage. Nausea; urge to urinate; flushed sensation; light-headedness; bad taste in mouth; abdominal discomfort; and dry mouth. Less frequently reported were: Anxiety; sweating; tightness in the throat; pressure in the chest; tingling sensation; drowsiness; and allergic reactions. Pharmacologically, TRH increases the release of the thyroid stimulating hormone (TSH) from the anterior pituitary. Prolactin release is also increased. It has recently been observed that approximately 65% of acromegalic patients tested respond with a rise in circulating growth hormone levels; the clinical significance is as yet not clear. Following intravenous administration, the mean plasma half-life of protirelin in normal subjects is approximately five minutes. TSH levels rise rapidly and reach a peak at 20 to 30 minutes. The decline in TSH levels takes place more slowly, approaching baseline levels after approximately three hours.