Renin-angiotensin system modulates renal bradykinin production

Previous studies have shown that sodium depletion is associated with an increase in renal kallikrein-kinin system activity. This system may play an important role in counterbalancing the renal effects of the renin-angiotensin system. In this study, we examined whether the renal renin-angiotensin system participates in the regulation of renal bradykinin (BK) levels during sodium depletion. We measured changes in renal excretory and hemodynamic function, renal interstitial fluid (RIF) BK, and RIF and urinary guanosine 3',5'-cyclic monophosphate (cGMP) and prostaglandin E2 (PGE2) in conscious uninephrectomized dogs (n = 5) in sodium metabolic balance (10 meq/day) in response to intrarenal arterial administration of the renin inhibitor ACRIP (0.2 microgram.kg-1.min-1) or angiotensin II AT1-receptor blocker losartan (100 ng.kg-1.min-1). ACRIP and losartan increased urine flow rate from 0.75 +/- 0.06 to 1.6 +/- 0.03 and 1.5 +/- 0.05 ml/min, respectively (each P < 0.001), and urine sodium excretion from 5.4 +/- 0.7 to 18.3 +/- 1.3 and 15.9 +/- 1.2 meq/min, respectively (each P < 0.001). Glomerular filtration rate and renal plasma flow increased only during losartan administration (P < 0.05). ACRIP decreased RIF BK by 48%, from 33.1 +/- 3.8 to 17.4 +/- 4.1 pg/min (P < 0.01). ACRIP decreased RIF cGMP by 38%, from 0.69 +/- 0.08 to 0.43 +/- 0.1 pmol/min (P < 0.01); urinary cGMP by 16%, from 0.63 +/- 0.05 to 0.53 +/- 0.02 pmol/min (P < 0.05); and RIF PGE2 by 46%, from 10.5 +/- 1.1 to 5.7 +/- 1.1 pg/min (P < 0.01). Urinary PGE2 was unchanged by ACRIP. Losartan decreased RIF PGE2 by 71%, from 10.8 +/- 0.6 to 3.1 +/- 0.6 pg/min (P < 0.01) but failed to change RIF BK, RIF cGMP, urinary cGMP, or urinary PGE2. These data suggest that the renin-angiotensin system tonically stimulates renal BK production and cGMP formation via a non-AT1 angiotensin receptor and renal PGE2 production via the AT1 receptor.