# Effects of intrarenal afferent stimulation by bradykinin on renal sympathetic nerve activity: tonic inhibition contributing to renal function

## TL;DR

This study shows that bradykinin reduces kidney sympathetic nerve activity, which may help the body excrete more sodium and water.

## Contribution

The study demonstrates that bradykinin induces tonic renal sympathodepression through afferent nerve stimulation.

## Key findings

- Intrarenal bradykinin decreases renal sympathetic nerve activity (RSNA) significantly.
- The effect of bradykinin is blocked by a B2-receptor antagonist but unmasked by an NK1-receptor blocker.
- Bradykinin's sympathodepressive effect is comparable to that of capsaicin.

## Abstract

Bradykinin (BK) may increase renal sodium excretion by decreasing tubular ENaC activity. Afferent renal nerve activity (ARNA) putatively controls renal sympathetic nerve activity (RSNA) involved in renal sodium handling. We recently found tonic sympatho-inhibition due to intrarenal ARNA stimulation by the TRPV1 agonist capsaicin (CAP). Since BK is known to augment TRPV1 effects, we hypothesized that intrarenally applied BK also tonically inhibits RSNA. Four groups of rats (n = 8; BK, CAP, HOE + BK, NaCl-control) were equipped with arterial and venous catheters for blood pressure (BP) and heart rate (HR) recordings and drug application; bipolar electrodes for RSNA and ARNA recordings, renal arterial catheter for intrarenal administration (IRA) of bradykinin (BK: 10−5 M, 20 µl and 10–4 M; 2.5, 5, 10 µl), capsaicin (CAP 3.3, 6.6, 10 and 33*10−7 M, 10 µl). The B2-receptor antagonist HOE-140 (10–4 M, 40 µl) was administered intravenously (IV) just before IRA BK (HOE + BK), finally the NK1-receptor blocker RP67580 (10−2 M, 15 µl; IV) was applied in all groups at the end of the experiment. IRA BK and CAP momentarily increased ARNA. IRA CAP, IRA BK, and IRA HOE + BK, decreased RSNA from 4.2 ± 0.8 to 1.3 ± 0.2 µV*sec (BK, P < 0.01), 3.6 ± 0.5 to 0.9 ± 0.2 µV*sec (CAP, P < 0.01) and 3.2 ± 0.3 to 0.8 ± 0.1 µV*sec (HOE-BK, P < 0.01). Suppressed RSNA (BK, CAP, HOE + BK) was unmasked by IV RP67580: 1.6 ± 0.5 to 8.6 ± 2.9 µV*sec (BK, P < 0.01); 1.0 ± 0.2 to 6.1 ± 1.5 µV*sec (CAP, P < 0.01); 0.8 ± 0.2 to 4.5 ± 0.8 µV*sec (HOE-BK, P < 0.05). IRA BK was associated with momentary increases of RSNA, abolished by HOE-140. Intrarenal stimulation of renal afferent nerves by BK induced tonic renal sympathodepression likely augmenting sodium and water excretion.