Identification of bradykinin in mammalian brain.

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 alpha-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.