Ulcerogen: a substance which causes ulcers. These are induced experimentally to investigated the effects of antiulcer treatments such as histamine antagonists and proton pump inhibitors. Examples include propionitrile which is a weak duodenal ulcerogen and cysteamine.

UK14,304: a non-subtype selective agonist of α2-adrenoceptors.

UN-0437: a selective D₂dopamine agonist.

Uncompetitive inhibition: a form of competition between a ligand and a receptor or substrate and enzyme which is not competitive, ie inhibition of the enzyme or receptor which is not due to substrate or ligand binding to the binding site but to another effects of the ligand on effector molecule. Typically, an uncompetitive inhibitor binds to the substrate-enzyme complex but not to the enzyme itself.

Uptake 1: a type of neuronal uptake in which aneurotransmitter is taken up by the presynaptic cell.

Uptake 2: a type of uptake in which a neurotransmitter is take up by non-neuronal cells in the vicinity of the site of transmitter release.

Ureidopenicillins: a class of penicillins comprising azlocillin, piperacillin and mezlocillin which are active against gram-negative bacteria such as Pseudomonas aeruginosa.

Urethane: a general anaesthetic used for laboratory animals. It is not applied to humans because large doses supress bone marrow function, stimulated the adrenal medulla and cortex and may be carcinogenic.??

Uricosuric: an agent causing the secretion of uric acid in the urine by acting direcyly on the renal tubule. Examples include probenecid and sulphinpyrazone. Uricosurics are used to increase urinary uric acid secretion and in the long-term treatment of gout in susceptible patients. Treatment can be indefinite in order to correct hyperglycemia.

Uroselective: a term used largely to describe compounds which act selectively in the lower urinary tract especially adrenoceptor antagonists which decrease vascular tone in this tissue.

Urotensin: a vasoactive cyclic 11-amino acid peptide and the endogenous ligand of the orphan G-protein-coupled receptor GPR14. U-II might be involved in the regulation of cardiovascular homeostasis and pathology. It is a potent vasoconstrictor peptide in isolated rat thoracic aorta and rat pulmonary arteries and represents a novel therapeutic target for management of a variety of cardiovascular diseases.

Ussing chamber: a chamber comprising two parts between which a membrane such as skin can be mounted in such as way as to facilitate the measurement of ions, atoms and molecules across the membrane. Named after Hans Ussing.