Hypothesis / aims of study
Nocturnal polyuria (NP) is the most common cause of nocturia, which decreases the quality of life of many elderly people. Previously, we have established a NP model mice and reported that decreased nitric oxide (NO) production leads to renal renin-angiotensin system (RAS) activation and salt-induced nocturnal polyuria [1]. However, the mechanism of renal RAS activation associated with decreased NO production is unclear. The aims of this study were to clarify their involvement in salt-induced nocturnal polyuria and to develop renal denervation (RDN) as a novel therapy for nocturnal polyuria via sympathetic nervous system modulation.
Study design, materials and methods
In Study 1, we evaluated the cerebral sympathetic nervous system activity and renal RAS activity in NP model mice. We used 19-week-old C57/BL6 male mice and divided them into 4 groups: normal salt diet (NSD), 1% high salt diet (HSD) , Nω-nitro-L-arginine methyl ester (L-NAME), and NP model mice treated with L-NAME and HSD (L-NAME + HSD). We evaluated the number of c-Fos positive cells in the hypothalamic paraventricular nucleus (PVN) as a measure of the cerebral sympathetic nervous system activity, and renal angiotensinogen (AGT) level as a measure of the renal RAS activity.
In Study 2, we evaluated the effect of renal denervation (RDN), which blocks the renal sympathetic nerves, on nocturnal polyuria. We used 17-week-old C57/BL6 male mice and divided them into 2 groups: Sham and RDN group. Both groups received L-NAME and HSD for 8 weeks, from two weeks after surgery. We compared renal angiotensinogen (AGT) level and inactive period urine rate as a measure of nocturnal polyuria between the two groups.
Results
In Study 1, the number of c-Fos–positive cells in the PVN of the L-NAME + HSD group was significantly higher than those of the NSD, HSD, and L-NAME group (27.5±3.1 vs. 3.5±1.0 vs. 9.7±1.1 vs. 8.0±1.6 cells/section, respectively; P < 0.01, Fig 1). Renal AGT/β-actin (ACTN) levels in the L-NAME + HSD group significantly exceeded those in the NSD, HSD, and L-NAME groups (1.44±0.17 vs. 0.44±0.08 vs. 0.64±0.12 vs. 0.80±0.11 arbitrary units, respectively; P < 0.01). These results indicate that the cerebral sympathetic nervous system and renal RAS of L-NAME + HSD group (NP model mice) are activated.
In Study 2, renal AGT/ACTN level in the RD group was also significantly lower than in the Sham group (1.07±0.09 vs. 1.60±0.14 arbitrary units, P < 0.01). In the Sham group, the DPi increased significantly (from 0.21±0.01 to 0.34±0.02, P < 0.001), while in the RD group, there were no significant DPi changes (from 0.20±0.01 to 0.18±0.02, P = 0.22) (Fig 2). These results indicate that RDN reduces renal RAS activity and improves nocturnal polyuria.
Figure 1.
The number of c-Fos-positive cells in the PVN in the NSD, HSD, L-NAME, and L-NAME + HSD (NP model mice) groups. *P < 0.01 (Tukey’s test) (n = 6, each group).
Figure 2.
Changes of inactive period urine rate in the Sham and RD groups. **P < 0.01 (paired t-test and two-way repeated measures ANOVA) (n = 6, each group).
Interpretation of results
Decreased NO and high salt intake activate cerebral sympathetic outflow, stimulating renal sympathetic nerves to enhance renal RAS. RDN disrupts this pathway, reducing RAS activity and normalizing inactive period urine rate.