Role of Renal Sympathetic Nerves in GLP-1 (Glucagon-Like Peptide-1) Receptor Agonist Exendin-4-Mediated Diuresis and Natriuresis in Diet-Induced Obese Rats

Background The gut-derived hormone GLP-1 (glucagon-like peptide-1) exerts beneficial effects against established risk factors for chronic kidney disease. GLP-1 influences renal function by stimulating diuresis and natriuresis and thus lowering arterial blood pressure. The role of the sympathetic nervous system has been implicated as an important link between obesity with elevated arterial pressure and chronic kidney disease. The primary aim of this study was to determine the contribution of renal sympathetic nerves on intrapelvic GLP-1-mediated diuresis and natriuresis in high-fat diet (HFD)-induced obese rats. Methods and Results Obesity was induced in rats by HFD for 12 weeks, followed by either surgical bilateral renal denervation or chronic subcutaneous endopeptidase neprilysin inhibition by sacubitril for a week. Diuretic and natriuretic responses to intrapelvic administration of the GLP-1R (GLP-1 receptor) agonist exendin-4 were monitored in anesthetized control and HFD rats. Renal GLP-1R expression and neprilysin expression and activity were measured. The effects of norepinephrine on the expression of GLP-1R and neprilysin in kidney epithelial LLC-PK1 cells were also examined. We found that diuretic and natriuretic responses to exendin-4 were significantly reduced in the HFD obese rats compared with the control rats (cumulative urine flow at 40 minutes, 387 +/- 32 versus 650 +/- 65 mu L/gkw; cumulative sodium excretion at 40 minutes, 42 +/- 5 versus 75 +/- 10 mu Eq/gkw, P<0.05). These responses in the HFD rats were restored after ablation of renal nerves (cumulative urine flow at 40 minutes, 625 +/- 62 versus 387 +/- 32 mu L/gkw; cumulative sodium excretion at 40 minutes, 70 +/- 9 versus 42 +/- 5 mu Eq/gkw, P<0.05). Renal denervation induced significant reductions in arterial pressure and heart rate responses to intrapelvic GLP-1 in the HFD rats. Renal denervation also significantly increased the GLP-1R expression and reduced neprilysin expression and activity in renal tissues from the HFD rats. Chronic subcutaneous neprilysin inhibition by sacubitril increased GLP-1-induced diuretic and natriuretic effects in the HFD rats. Finally, exposure of the renal epithelial cells to norepinephrine in vitro led to downregulation of GLP-1R expression but upregulation of neprilysin expression and activity. Conclusions These results suggest that renal sympathetic nerve activation contributes to the blunted diuretic and natriuretic effects of GLP-1 in HFD obese rats. This study provides significant novel insight into the potential renal nerve-neprilysin-GLP-1 pathway involved in renal dysfunction during obesity that leads to hypertension.