The characterization of radioimmunoassay for rat pancreatic polypeptide in serum

A radioimmunoassay for the measurement of rat pancreatic polypeptide (RPP) in serum or plasma has been developed and characterized using a new guinea-pig anti-rat-PP antibody. The assay provides a high degree of sensitivity and lacks cross-reactivity (CR less than 0.01%) to neuropeptide Y and peptide YY. It also does not interact with PPs of other species or peptide hormones namely, amylin, glucagon, human insulin, human-PP, human-proinsulin, rat C-peptide and rat insulin. The assay employs synthetic rat PP as standards from concentrations of 21-2100 pg/ml (i.e., 5-500 pM) and produces a sensitivity limit of 19 pg/ml (4.5 pM) PP at +/- 3 S.D. The intra- and interassay % coefficient of variations are 6.4% and 5.9%, respectively. The % recovery of RPP added to rat serum samples ranges from 98% to 103%. Assay of serum volumes ranging from 25 microliters to 100 microliters does not significantly alter the expected RPP level. The migration patterns of rat serum PP and that of a synthetic RPP are identical by Sephadex G-50 chromatographic analysis. The mean values of fasting and a 2 h post-feeding plasma RPP levels in normal rats are 40 +/- 2 and 80 +/- 10 pg/ml (9.5 pM and 19.0 pM), respectively. Rat-PP release during insulin induced hypoglycemia in conscious rats rises from 38 +/- 5 pg/ml to 261 +/- 34 pg/ml (9.0 to 62.1 pM, P less than 0.005) by 30 min. Additionally, the antibody used in this study cross-reacts well with mouse-PP as determined by linear serum dilution curves, thus making it useful in the measurement of murine-PP. In conclusion, we have developed and validated a sensitive and specific rat-PP assay. This assay provides a new tool for the reliable measurement of PP in physiologic studies using rat and mouse animal models