Bombesin-like activity: Radioimmunologic assessment in biological tissues

Abstract Highly specific sensitive radioimmunoassays (RIA) have been developed to quantitatively measure the anuran skin peptide, bombesin. These RIA's have been used to demonstrate a bombesin-like immunoactivity (BLI) within mammalian brain, gut, lung and plasma. BLI in rat brain is present in highest concentration in the hypothalamus, with lowest concentration in cerebellum. The highest concentrations of BLI outside the brain are found in the stomach, duodenum and jejunum, with lower levels in the lung. No BLI was detected in pineal, anterior pituitary, adrenal, liver, kidney or pancreas. While BLI was not detected in normal rat plasma, extraction of plasma with formic acid revealed the presence of significant amounts of BLI in normal rat plasma. Gel filtration of acidified rat plasma BLI produced a single peak of BLI, which appears to be of higher molecular weight than frog skin bombesin. Gel filtration of formic acid extracts of rat gastrointestinal tract demonstrated the presence of two forms of BLI; a large BLI and a smaller BLI similar in size to plasma BLI.