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.

Cyanocobalamin Co-58 is radiopharmaceutical derivative of an essential vitamin B12. Radioactive isotope Co-58 has a half-life of 72 days and produces hard gamma radiation when it decays to Fe-58. In the 1960s, cyanocobalamin Co-58 was used in western European countries for the diagnosis of liver diseases: hepatitis, parenchymal liver disease, lead poisoning, and other condition. Its use was superseded by cyanocobalamin Co-57, which is marketed used for the diagnosis of pernicious anemia and as a diagnostic adjunct in other defects of intestinal vitamin B12 absorption.

Pentagastrin (trade name Peptavlon) is a cholecystokinin type B (CCK(B)) receptor agonist, which was indicated as a diagnostic aid for evaluation of gastric acid secretory function. It was effective in testing for an acidity (achlorhydria) in patients with suspected pernicious anemia, atrophic gastritis, or gastric carcinoma. It was effective in determining the reduction in acid output after operations for peptic ulcer, such as vagotomy or gastric resection. Pentagastrin was also indicated as a diagnostic aid in testing for gastric hypersecretion in patients with suspected duodenal ulcer or postoperative stomal ulcer, and for the diagnosis of Zollinger-Ellison tumor. Peptavlon was discontinued, Federal Register determined that product was not discontinued or withdrawn for safety or efficacy reasons. In addition was shown, that Pentagastrin may release adrenocorticotropin (ACTH) and cortisol through direct pharmacological action, perhaps enhanced on first exposure by psychologically mediated novelty effects. Novelty, per se, is not likely the primary mediator of the hypothalamic-pituitary-adrenal (HPA) response. This model may be useful for further study of cognitive-emotional modulators of HPA axis activity.

Cyanocobalamin Co 57 is a manufactured form of radiolabeled vitamin B indicated as an adjunct in diagnosing intestinal cyanocobalamin malabsorption syndromes due to lack of intrinsic factor (IF) or other defects in intestinal absorption (e.g., blind loop syndrome and diverticulitis, celiac disease, Crohn's disease, lesions in the small intestine, severe pancreatitis, tropical sprue).

Iocetamic acid is a medical diagnostic aid. It is a contrast agent used to enhance structures or fluids during X-ray imaging.

Metrizoic acid is a diagnostic radiopaque that usually occurs as the sodium salt. The mechanism of action of metrizoic acid is as a X-Ray Contrast Activity.

Tyropanic acid and its salt sodium tyropanoate are radiocontrast agents used in cholecystography (X-ray diagnosis of gallstones). Tyropanic acid is sold under the trade names Bilopaque, Lumopaque, Tyropaque, and Bilopac. The molecule contains three heavy iodine atoms which obstruct X-rays in the same way as the calcium in bones to produce a visible image. After injection it is rapidly excreted into the bile.

IODOHIPPURIC ACID I-131 (ortho-Iodohippuric Acid I-131, [I-123]-OIH) is an iodine-containing compound used in pyelography as a radiopaque medium. Iodine-123 labelled ortho-Iodohippuric acid was used in the early 1970's as a kidney imaging agent or tracer that "lights-up" inside your body when scanned, but over the years its use has declined. [I-123]-OIH is primarily extracted by the renal tubules and has excellent pharmacokinetic properties, with a clearance only slightly less than that of p-aminohippuran, but its use has been compromised by the suboptimal imaging characteristics of the 364-keV photon of 131I and the delivery of relatively high radiation doses to kidneys and thyroid in patients with impaired renal function

Iopanoic acid and ipodate salts have been used for oral cholangiography to visualize the biliary ducts. Ipodate salts have been used for the long-term treatment of Graves' disease and in hyperthyroidism. Ipodate reduced levels of T3 and T4 in the patients. Ipodate also inhibits the conversion of T4 to T3. It is not considered a first-line approach. Ipodate sodium lacks FDA approval for these uses. During investigation of mechanism of action was discovered, that binding of sodium ipodate with nuclear T3 receptors was not a prominent mechanism via which the drug attenuates T3 effects in vivo. Sodium ipodate could enhance T3 effects at the cellular level and that enhancement could not be reflected by routinely monitored serum TSH.

Iopydol is an X-ray contrast medium used in conjunction with iopydone as the proprietary preparation, Hytrast, for the bronchography.