Kinins in humans

The kinin peptide system in humans is complex. Whereas plasma kallikrein ge nerates bradykinin peptides, glandular kallikrein generates kallidin peptid es. Moreover, a proportion of kinin peptides is hydroxylated on proline(3) of the bradykinin sequence. We established HPLC-based radioimmunoassays for nonhydroxylated and hydroxylated bradykinin and kallidin peptides and thei r metabolites in blood and urine. Both nonhydroxylated and hydroxylated bra dykinin and kallidin peptides were identified in human blood and urine, alt hough the levels in blood were often below the assay detection limit. Where as kallidin peptides were more abundant than bradykinin peptides in urine, bradykinin peptides were more abundant in blood. Bradykinin and kallidin pe ptide levels were higher in venous than arterial blood. Angiotensin-convert ing enzyme inhibition increased blood levels of bradykinin, but not kallidi n, peptides. Reactive hyperemia had no effect on antecubital venous levels of bradykinin or kallidin peptide levels. These studies demonstrate differe ntial regulation of the bradykinin and kallidin peptide systems, and indica te that blood levels of bradykinin peptides are more responsive to angioten sin-converting enzyme inhibition than blood levels of kallidin peptides.