IN-VIVO METABOLISM OF SUBSTANCE-P IN RAT STRIATUM UTILIZING MICRODIALYSIS LIQUID-CHROMATOGRAPHY MICRO-ELECTROSPRAY MASS-SPECTROMETRY

In vivo microdialysis in combination with liquid chromatography/micro-electrospray mass spectrometry was used to study the metabolism of substance P in rat brain. A microdialysis probe was used both to introduce substance P into the brain and to collect metabolic products. Unilateral infusions of 25 and 50 pmol mu l(-1) substance P, or isotopically labeled [D-8-Phe(8)] substance P, at flow rates of 0.3 mu l min(-1), were made through the microdialysis probe implanted in the striatum of anesthetized rats. The metabolic products were analyzed by bn-line mass spectrometry and the results showed that substance P, an 11 amino acid residue polypeptide, was metabolized in tbe striatum to form N-terminal fragments 1-9, 1-8 and 1-7; C-terminal fragments 3-11, 5-11, 6-11, 7-11 and 8-11; and internal fragments 4-8, 6-10 and 7-10. The concentrations of these metabolites in dialysates were measured in order to compare the relative importance of several possible metabolic degradative pathways.