Stimulation of renal interstitial bradykinin by sodium depletion

The ability to measure and detect change in renal bradykinin in situ would allow study of relations between local kinin production and renal function in hypertensive or diabetic disorders. A new renal interstitial microdialysis technique allowed collections of renal subcapsular interstitial fluid 2 weeks after microdialysis probe placement in conscious dogs (n = 5) on a normal sodium diet (50 mEq/day) and for 5 subsequent days on low sodium intake (10 mEq/day). Although interstitial bradykinin measured by radioimmunoassay (RIA) was undetectable (< 0.08 pg/min) during normal sodium intake, it was detectable (0.34 +/- 0.02 pg/min) after 1 day of low sodium. The kinin level at the end of the 5 subsequent days on low sodium was 1.94 +/- 0.09 pg/min (P < .01). The data show that renal interstitial kinin can be measured in situ. Further, a low sodium diet can rapidly increase interstitial kinin in the conscious dog.