Electrical stimulation of renal nerves for modulating urine glucose excretion in rats

Abstract

Background: The role of the kidney in glucose homeostasis has gained global interest. Kidneys are innervated by renal nerves, and renal denervation animal models have shown improved glucose regulation. We hypothesized that stimulation of renal nerves at kilohertz frequencies, which can block propagation of action potentials, would increase urine glucose excretion. Conversely, we hypothesized that low frequency stimulation, which has been shown to increase renal nerve activity, would decrease urine glucose excretion.

Methods: We performed non-survival experiments on male rats under thiobutabarbital anesthesia. A cuff electrode was placed around the left renal artery, encircling the renal nerves. Ureters were cannulated bilaterally to obtain urine samples from each kidney independently for comparison. Renal nerves were stimulated at kilohertz frequencies (1-50 kHz) or low frequencies (2-5 Hz), with intravenous administration of a glucose bolus shortly into the 25-40-min stimulation period. Urine samples were collected at 5-10-min intervals, and colorimetric assays were used to quantify glucose excretion and concentration between stimulated and non-stimulated kidneys. A Kruskal-Wallis test was performed across all stimulation frequencies (α = 0.05), followed by a post-hoc Wilcoxon rank sum test with Bonferroni correction (α = 0.005).

Results: For kilohertz frequency trials, the stimulated kidney yielded a higher average total urine glucose excretion at 33 kHz (+ 24.5%; n = 9) than 1 kHz (- 5.9%; n = 6) and 50 kHz (+ 2.3%; n = 14). In low frequency stimulation trials, 5 Hz stimulation led to a lower average total urine glucose excretion (- 40.4%; n = 6) than 2 Hz (- 27.2%; n = 5). The average total urine glucose excretion between 33 kHz and 5 Hz was statistically significant (p < 0.005). Similar outcomes were observed for urine flow rate, which may suggest an associated response. No trends or statistical significance were observed for urine glucose concentrations.

Conclusion: To our knowledge, this is the first study to investigate electrical stimulation of renal nerves to modulate urine glucose excretion. Our experimental results show that stimulation of renal nerves may modulate urine glucose excretion, however, this response may be associated with urine flow rate. Future work is needed to examine the underlying mechanisms and identify approaches for enhancing regulation of glucose excretion.

Keywords: Electrical stimulation; Glucose; Glycosuria; Kidney; Renal nerve; Urine.

Fig. 1

Experimental setup diagram and protocol timeline. a Experimental setup: Jugular vein was cannulated for saline and glucose infusion. Nerve cuff electrode was placed on renal nerves of the left kidney and connected to a stimulation generator. Ureters were cannulated bilaterally, and urine samples were collected in sampling vials. b Nerve cuff electrode was placed around the renal artery, encapsulating the renal nerve branches that run along the renal artery. c Timeline for experimental protocol: Each experiment consisted of 1–3 stimulation trials (T₁-T₃), with a rest period (R) before each trial. A glucose bolus was infused in each trial. Blood glucose measurements and urine samples were obtained periodically throughout the trials

Fig. 2

Changes in urine glucose excretion. a The percentage difference in urine glucose excretion between the stimulated and non-stimulated kidney (∆UGE) at the applied stimulation frequencies. Stimulation frequency had a statistically significant main effect (Kruskal-Wallis test, p < 0.05), with one within-frequency comparison being significant (5 Hz and 33 kHz, post-hoc Wilcoxon rank sum test, * = p < 0.005). b Representative stimulation trial at 33 kHz that showed an increase in UGE. c Representative stimulation trial at 33 kHz that showed no apparent effect on UGE. d Representative stimulation trial at 33 kHz that showed a decrease in UGE

Fig. 3

Changes in urine glucose concentration. a The percentage difference between the area under the curve for urine glucose concentration of the stimulated and non-stimulated kidney (∆AUC_UGC) at the applied stimulation frequencies. b Urine glucose concentration (UGC) measurements for the trial shown in Fig. 2b. c UGC measurements for the trial shown in Fig. 2c. d UGC measurements for the trial shown in Fig. 2d

Fig. 4

Changes in urine flow rate. a The percentage difference between the area under the curve for urine flow rate of the stimulated and non-stimulated kidney (∆AUC_UFR) at the applied stimulation frequencies. Stimulation frequency had a significant main effect (Kruskal-Wallis test, p < 0.05), with 5 Hz and 33 kHz trials significantly different from each other (post-hoc Wilcoxon rank sum test, * = p < 0.005). b Urine flow rate (UFR) measurements for the trial shown in Fig. 2b. c UFR measurements for the trial shown in Fig. 2c. d UFR measurements for the trial shown in Fig. 2d

Fig. 5

Changes in blood glucose concentration. a The blood glucose concentration decrease rate (BGCDR) at the applied stimulation frequencies. b Blood glucose concentration (BGC) measurements and BGCDR (slope) for the trial shown in Fig. 2b. c BGC and BGCDR measurements for the trial shown in Fig. 2c. d BGC and BGCDR measurements for the trial shown in Fig. 2d. BGC measurements above 750 mg/dL were not available due to the limitations of the glucometer