MSI_000003360

Indigo carmine, also known as C.I. Pigment Blue 63, or indigo blue, belongs to the class of organic compounds known as indolines. Indolines are compounds containing an indole moiety, which consists of pyrrolidine ring fused to benzene to form 2,3-dihydroindole. Indigo carmine is an indigo derivative that is produced by sulfonation of indigo, which makes the compound water soluble (up to 10 g/L). Indigo carmine exists as a bright purple solid and is an extremely weak basic (essentially neutral) compound (based on its pKa). It is approved for use as a food colorant in the U.S and E.U. It is also used as a medical dye. In obstetric surgery, indigo carmine solutions are sometimes employed to detect amniotic fluid leaks. In urologic surgery, intravenous injection of indigo carmine is often used to highlight portions of the urinary tract. The dye is filtered rapidly by the kidneys from the blood, and colors the urine blue. This enables structures of the urinary tract to be seen in the surgical field and demonstrates if there is a leak. A frequently encountered cardiovascular effect of intravenous indigo carmine administration is temporary alpha-receptor stimulation. Skin discoloration may occur at high doses. According to one study, the primary action of indigo carmine appears to be at the level of nitric oxide generation and/or its release from the endothelium. In addition to this, indigo carmine appears to inhibit vascular smooth muscle guanylyl cyclase. Therefore, indigo carmine may increase blood pressure by interfering with these nitric oxide-mediated vasodilatory mechanisms. Moreover, incubation of isotopically labeled indigo carmine with intestinal contents of rats for 48 h suggested that isatin-5-sulphonic acid and 5-sulphoanthranilic acid may possibly be metabolites formed by intestinal bacterial metabolism of the drug. D004396 - Coloring Agents