RADIOIMMUNOASSAY OF SUBSTANCE-P IN LUNG PERFUSATE

A radioimmunoassay of the undecapeptide substance P (SP) and its appli cation in rabbit lung superfusate has been developed. The assay was ba sed on the use of a radioactive tracer, I-125-SP-Tyr8, which showed, w ith an excess of antibodies, a specific binding greater than 90% and a nonspecific binding lower than 2%. This tracer was stable for 4 weeks at -20 degrees C. Its specific radioactivity was 384 Ci/mmol. The ass ay's lower limit of detection was 10 pg/ml (0.7 fmol). The determinati on of SP in rabbit lung perfusate required extraction and concentratio n using octadecylsilane cartridges. Under these conditions, the recove ry of SP from experiments on lung perfusates (n = 4) was 75.0 +/- 4.5% , and the intraassay and interassay coefficients of variation were 7.3 +/- 1.9% and 10.7 +/- 1.3%, respectively. Amounts of SP released in r abbit lung perfusates were determined following stimulation of pulmona ry C fibers with capsaicin (10(-4) M). During the stimulation period, the values of SP from lung perfusates (n = 6) increased significantly when compared with baseline values. (C) 1998 Elsevier Science Inc.