The distribution of the newly characterized peptide somatostatin-28(1-12) was determined in rattis-sues using a radioimmunoassay in which the immune plasma is directed against the C-terminus of the dodecapept ide. In the central nervous system, somatostatin-28(1-12)-like immunoreactivity 1s highly concentrated in the hypothalamus and the amygdala. In the digestive system, the highest levels of immunoreactivity are found 1n the stomach, the pancreas and the colon. The immunoreactive material measured in d i f f e r e n t tissues 1s heterogenous: in addition to the dodecapeptide, two N-term1nally extended somatostatin-28(1-12) peptides of 4,400 and 8,000 mol wt are also detected by the immune plasma. However, the dodecapeptide it selfusually accounts for the majority (66 to 75%) of the total somatostatin-28(1-12)-Hke Immunoreactivity present in those tissues.
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