U46619 is a stable synthetic analog of the endoperoxide prostaglandin PGH<sub>2</sub> first prepared in 1975, and acts as a thromboxane A<sub>2</sub> (TP) receptor agonist. It potently stimulates TP receptor-mediated, but not other prostaglandin receptor-mediated responses in various in vitro preparations and exhibits many properties similar to thromboxane A<sub>2</sub>, including shape change and aggregation of platelets and smooth muscle contraction. U46619 is a vasoconstrictor that mimics the hydroosmotic effect of vasopressin.