Correlation of substance P-induced desensitization with substance P amino terminal metabolites in the mouse spinal cord.
Intrathecal injection of mice with substance P (SP) or its C-terminal fragments results in a behavioral syndrome characterized by reciprocal caudally directed biting and scratching. Repeated injection of SP, but not SP C-terminal fragments, results in a decrease in the intensity of, or desensitization to, these SP-induced behaviors. Peptidase inhibitors, phosphoramidon (PH), bacitracin (BAC), diprotin A (DPA) and angiotensin converting enzyme inhibitor (ACEI OR SQ20881), together with [3H]SP, were used to investigate the possible accumulation of tritiated N-terminal metabolites in the mouse spinal cord in vivo during the development of desensitization to SP. SP N-terminal metabolites in the spinal cord were quantified by reverse-phase HPLC. The magnitude of SP-induced desensitization correlated well (r = .95) with total SP N-terminal metabolites recovered from the spinal cords of the same mice studied in vivo. The magnitude of SP-induced desensitization was also found to be negatively correlated (r = .95) with total recovered intact [3H]SP. The rank order of potency of the peptidase inhibitors in decreasing the magnitude of SP-induced desensitization was BAC = PH much greater than ACEI greater than DPA. The order of potency for in vitro inhibition of SP metabolism using synaptic membrane-derived peptidases was BAC greater than PH much greater than ACEI. These results support the hypothesis that desensitization to SP-induced behaviors depends, at least in part, on the concentration of SP N-terminal metabolites in the spinal cord.
University of Minnesota, College of Veterinary Medicine, Department of Veterinary Biology, St. Paul 55108.
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Igwe
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Sun
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Larson
D000595:Amino Acid Sequence; D000818:Animals; D001522:Behavior, Animal / Q000187:drug effects*; D002851:Chromatography, High Pressure Liquid; D006868:Hydrolysis; D007278:Injections, Spinal; D008297:Male; D051379:Mice; D008969:Molecular Sequence Data; D013116:Spinal Cord / Q000378:metabolism*; D013373:Substance P / Q000378:metabolism / Q000494:pharmacology*
D013373:Substance P