Development and characterization of a specific and sensitive radioimmunoassay for rat galanin: measurement in brain tissue, hypophyseal portal and peripheral serum.

Galanin (GAL), a 29 amino acid peptide, is extensively distributed in both brain and intestine having been described as a putative neuroendocrine modulator. Up to this date, available radioimmunoassays for measuring GAL have the problem of nonparallel responses when rat biological samples are used. Due to the recent availability of synthetic rat GAL (rGAL), we pursued the development of a specific RIA for rGAL. Our RIA system presents a high specificity since porcine GAL (pGAL), which differs from rGAL in three carboxy-terminus substitutions, displays negligible crossreactivity. In addition, in the RIA a sensitivity of at least 1 pg/tube can be obtained. All biological samples tested in this study (serum samples from both peripheral and portal blood and arcuate-nucleus median eminence extracts) displayed perfect parallelism to synthetic rGAL standard. The RIA is suitable for measuring minute amounts of rGAL directly in serum samples from both portal and peripheral circulation. Interestingly, the IC50 for portal serum was approximately 10-fold lower than that for peripheral serum. This indicates that rGAL may be present in higher concentrations in portal than in peripheral blood. In addition, our data suggest that the pituitary gland contributes approximately 30% to the total levels of rGAL measured in peripheral serum. Together, this data reinforces the concept that GAL is involved in mechanisms controlling and/or regulating neuroendocrine functions.