Melanuria

MELANURIA, the excretion with urine of pigments of dark brown or brown color, which easily darken or blacken from contact with oxygen in the air. The pigments excreted with urine represent chemically a series of different substances of protein origin, serving as so-called chromogens, i.e., pigment-formers. Chromogens, in this case melanogens, are those substances which, oxidizing in the air, are converted into melanins. The origin of melanins is the same as that of the pigments of melanotic tumors, so-called melanomas_; This is the difference between true urinary melanins and the pigments found in the dark brown urine excreted by patients with various poisonings (phenol, pyrogallol, hydroquinone, etc.), as well as the dark brown urine of alkaptonurics (see Alkaptonuria). Melanins originate from proteinochrome (Nentsky), i.e., from the pigment-forming complex of the protein molecule. It typically contains the aromatic acid tryptophan, as well as a sulfur-rich chromogen. Clinically, M. is observed in the presence of a melanin-forming tumor in the body, especially during its period of decay. M. therefore most often appears in melanomas of the liver and serves as an early and at the same time extremely grave diagnostic symptom. M. is already detected by simple inspection of the urine; however, more precise recognition of it is only possible by means of precipitating the melanins with barium water followed by the addition of lead sugar to the filtrate; both precipitates give with a concentrated solution of soda a dark brown pigment, difficultly soluble in acetic acid. Those melanins which can be dissolved in strong alkalis do not give a typical absorption sector, but merely weaken the diffusely passing spectral colors.