BRADYKININ PEPTIDES IN KIDNEY, BLOOD, AND OTHER TISSUES OF THE RAT

The bradykinin peptide system is a tissue-based system with potent cardiovascular and renal effects. To investigate the regulation of this system, we developed a highly sensitive amino terminal-directed radioimmunoassay that, with high performance liquid chromatography, enables the measurement of bradykinin-(1-7), bradykinin-(1-8), and bradykinin-(1-9). Together with a carboxy terminal-directed radioimmunoassay, we characterized bradykinin peptides in rat kidney and blood. The predominant bradykinin peptides in kidney were bradykinin-(1-9) (approximately 100 fmol/g wet weight of tissue) and bradykinin-(1-7) (approximately 70 fmol/g), with low levels of bradykinin-(1-8) (approximately 8 fmol/g) and bradykinin-(4-9) (approximately 12 fmol/g) detectable; bradykinin-(2-9) and bradykinin-(3-9) were below the limits of detection. In blood, the levels of bradykinin-(1-9) were very low (approximately 2 fmol/ml), and other bradykinin peptides were below the limits of detection. Ile,Ser-bradykinin and Met,Ile,Ser-bradykinin were below the limits of detection in both kidney and blood, indicating that T-kininogen makes no detectable contribution to renal or circulating bradykinin peptides. Administration of the angiotensin converting enzyme inhibitor perindopril was associated with an approximate twofold increase in renal levels of bradykinin-(1-8) and bradykinin-(1-9) and a decrease in the bradykinin-(1-7)/bradykinin-(1-9) ratio. The amino terminal-directed radioimmunoassay was also applied to heart, aorta, brown adipose tissue, adrenal, lung, and brain. For these tissues, bradykinin-(1-7) and bradykinin-(1-9) were of similar abundance (16-340 fmol/g), with lower levels of bradykinin-(1-8). These studies demonstrate that tissue levels of bradykinin peptides are much higher than circulating levels, consistent with their formation at a local tissue site. Of peptides derived from K-kininogen, bradykinin-(1-9) is the predominant bioactive peptide in all tissues, and a major pathway of bradykinin-(1-9) metabolism involves the formation of bradykinin-(1-7). In kidney, angiotensin converting enzyme plays an important role in bradykinin-(1-9) metabolism, and increased bradykinin-(1-9) and bradykinin-(1-8) levels may mediate in part the renal effects of converting enzyme inhibition.