Analytical extraction of regulatory peptides from rat lung tissue

We evaluated protocols for the extraction of calcitonin gene-related peptide, neuropeptide Y, substance P, peptide YY and beta-endorphin from rat lung tissue for subsequent radioimmunoassay. The effects of varying acidity of the extraction solution and repeating extraction on the recovery of peptide immunoreactivity and non-specific tracer-binding were compared by analysis of variance. Moreover, variability of immunoreactivity was quantified for comparison. Considering all three criteria, the optimal acidity for extraction was: 0.1 M or 1 M acetic acid for CGRP and beta-endorphin, 0.1 M acetic acid for NPY, 1 M acetic acid for substance P and phosphate buffer for peptide YY. Double or combined extraction unambiguously improved assay results only for substance P. Reversed-phase high-performance liquid chromatography of CGRP-, NPY- and SP-immunoreactivity obtained from selected extracts suggested that differences in recovery of these peptides are not explainable by differential peptide fragmentation during extraction.