Identification of Bradykinin in Mammalian Brain

Abstract: Bradykinin‐like activity was purified from acetic acid extracts of saline‐perfused rat brains by gel filtration chromatography and two reverse‐phase HPLC systems capable of resolving bradykinin from lysyl‐bradykinin and other bradykinin analogs and fragments. Addition of [³H]bradykinin to extracts permitted calculation of recoveries and monitoring of chromatographic fractions. Fractions were examined by radioimmunoassay using a potent and highly specific antiserum raised against bradykinin‐human albumin conjugates in rabbits. Bradykinin receptor‐active material was also measured by radioreceptor assay using guinea pig ileum, as well as by a bioassay with the estrous rat uterus. Active material chromatographed as authentic bradykinin in all systems. Levels of 0.6 pmol/g whole rat brain were detected, with eight times higher levels in the hypothalamus. Activity increased up to 10‐fold following treatment with trypsin; treatment with α‐chymotrypsin or angiotensin‐converting enzyme substantially reduced activity. Similar levels and distribution of bradykinin‐like activity were also detected in guinea pig brain extracts. These data substantiate the existence of authentic bradykinin in mammalian brain.