Regional Distribution and Characterization of Kinin in the CNS of the Rat

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Abstract
The distribution of kinin in the CNS of the rat, which was extracted with n‐butanol from an acidified homogenate, was determined using a bradykinin (BK) radioimmunoassay system. The immunoreactive kinin was widely distributed throughout the brain. The highest content was found in the pituitary gland (4,135 fmol BK Eq/g), followed by the medulla oblongata (912 fmol/g), cerebellum (549 fmol/g), and cortex (512 fmol/g). The kinin in the posterior pituitary was concentrated 4.5 times as much as in the anterior lobe. Serial dilution of brain extracts produced binding curves parallel to the standard radioimmunoassay curve. The purified brain kinin comigrated with authentic BK during CM‐cellulose chroma tography and Sephadex LH‐20 gel chromatography. Its molecular weight was estimated to be 1,127$45 by gel filtration, which coincides well with that of BK. Chymotrypsin degraded the extracted kinin and authentic BK, but trypsin did not. These data demonstrate that a peptide indistinguishable from BK exists in the rat brain. Furthermore, pituitary kinin was separated into BK (87%), Lys‐BK (10%), and Met‐Lys‐BK (3%), using reverse phase HPLC.