Effects of Sex and Anesthetics on Renal Sensory Nerve Responses
Authors: DeLalio Leon , Stocker Sean 
Published: April 2020

The anti‐hypertensive effects of renal denervation are partly attributed to denervation of renal sensory nerves, which detect changes in intrarenal pressure and nociceptive chemokines to reflexively alter sympathetic nerve activity, renal function, and blood pressure. To date, the majority of experiments have assessed renal sensory responses using either anesthesia and exclusively male animals. The purpose of the present study was to evaluate the impact of anesthesia and sex on in vivo renal afferent nerve activity (ARNA) to chemo‐ and mechano‐sensitive stimuli. Male and female Sprague‐Dawley rats (250–400g) were assessed by multifiber nerve recordings in unanesthetized decerebrate preparations, Inactin, isoflurane, or urethane anesthesia. Baseline ARNA was not different across preparations or between sexes (n=6–8/group): decerebration (M: 20±6Hz, F: 20±6Hz), Inactin (M:12±5Hz, F: 16±8 Hz), and isoflurane (M: 23±6Hz, F: 29±6Hz). However, ARNA was significantly lower in urethane‐anesthetized male rats (M: 3±1Hz, F: 29±6Hz; p<0.05).

To evaluate chemosensitive responses, increasing doses of capsaicin [0 – 50 μM], (50μL over 15 s) were infused into the renal artery via a suprarenal arterial catheter, which produced concentration‐dependent increase in ARNA in all groups (n=4–6/group). ARNA was most sensitive in decerebrate and Inactin vs isoflurane or urethane groups. In male rats, the threshold concentration of capsaicin to evoke a response was 1μM decerebrate (117.8±29.2Hz, p=0.02) < 10μM Inactin (137.0±61.0, p=0.0002) < 30μM isoflurane (102.2±37.8, p=0.02) = 30μM urethane (96.5±35.9, p=0.02). In female rats, the threshold was 1μM Inactin (117.2±37.5Hz, p=0.03) < 10μM decerebrate (184.8±41.6, p=0.03) = 10μ isoflurane (93.5±10.4, p=0.02) < 30μM urethane (158.8±47.6, p=0.02).

To evaluate mechanosensitive responses, renal artery occlusion (30s) increased ARNA equally in all groups. However, a significant sex effect was observed using Isoflurane (M: 9±4Hz, F: 33±3Hz; p<0.01). Lastly, 5‐mmHg stepwise increases in renal pelvic pressure (0–30mmHg, 30s) produced linear increases in ARNA in all groups. Using linear regression to test the magnitude (y‐intercept) and sensitivity (slope) of ARNA we found significant differences in the magnitude of males (n=6–8/group): decerebrate, 6.5±5.3Hz; Inactin, 15.7±3.4 Hz; isoflurane, 3.8±3.2Hz; urethane, 0.2±1.1Hz; p<0.0001) and females (n=4–7/group): decerebrate, 8.8±10.5Hz; inactin, 9.5±6.0Hz; isoflurane, 14.2±8.6Hz; urethane, 0.2±4.5Hz; p<0.0001). Between sex comparisons resulted in blunted male sensitivity to urethane (M: slope=0.1±0.1; F: slope=0.7±0.23, p<0.001), and elevated female sensitivity to isoflurane (M: slope=0.1±0.2, F: slope=1.1±0.4, p<0.03). Decerebrate and inactin anesthesia were similarly sensitive between sexes.

In conclusion, ARNA to chemo‐ and mechano‐sensitive stimuli were similar between an unanesthetized‐decerebrate preparation vs Inactin anesthesia. Isoflurane and urethane attenuated ARNA to capsaicin and differentially altered ARNA to increased renal pelvic pressure. Sex did not consistently impact ARNA per se, but sex differences were linked to the use of isoflurane and urethane. These findings suggest decerebration or Inactin anesthesia should be employed to study renal afferent nerve function.

Support or Funding Information

NIH Grants: R01 HL145875