Role of substance P in renal injury during DOCA-salt hypertension

Abstract

Substance P (SP), a neurokinin-1 receptor (NK-1R) agonist, is mainly produced and stored in primary sensory nerves and, upon its release, participates in cardiovascular and renal functional regulation. This study tests the hypothesis that activation of the NK-1Rs by SP occurs during hypertension induced by deoxycorticosterone (DOCA)-salt treatment, which contributes to renal injury in this model. C57BL/6 mice were subjected to uninephrectomy and DOCA-salt treatment in the presence or absence of administration of selective NK-1 antagonists, L-733,060 (20 mg/kg·d, ip) or RP-67580 (8 mg/kg·d, ip). Five weeks after the treatment, mean arterial pressure determined by the telemetry system increased in DOCA-salt mice but without difference between NK-1R antagonist-treated or NK-1R antagonist-untreated DOCA-salt groups. Plasma SP levels were increased in DOCA-salt compared with control mice (P < 0.05). Renal hypertrophy and increased urinary 8-isoprostane and albumin excretion were observed in DOCA-salt compared with control mice (P < 0.05). Periodic acid-Schiff and Masson's trichrome staining showed more severe glomerulosclerosis and tubulointerstitial injury in the renal cortex in DOCA-salt compared with control mice, respectively (P < 0.05). Hydroxyproline assay and F4/80-staining showed that renal collagen levels and interstitial monocyte/macrophage infiltration were greater in DOCA-salt compared with control mice, respectively (P < 0.05). Blockade of the NK-1R with L-733,060 or RP-67580 in DOCA-salt mice suppressed increments in urinary 8-isoprostane and albumin excretion, interstitial monocyte/macrophage infiltration, and glomerulosclerosis and tubulointerstitial injury and fibrosis (P < 0.05). Thus, our data show that blockade of the NK-1Rs alleviates renal functional and tissue injury in the absence of alteration in blood pressure in DOCA-salt-hypertensive mice. The results suggest that elevated SP levels during DOCA-salt hypertension play a significant role contributing to renal damage possibly via enhancing oxidative stress and macrophage infiltration of the kidney.

Fig. 1.

Changes in MAP and HR in DOCA-salt-hypertensive mice with or without L-733,060 treatment. Graphs representing daily average 24-h MAP (A) and HR (B). Values are means ± se (n = 4).

Fig. 2.

MAP and HR in DOCA-salt-hypertensive mice with or without L-733,060 treatment at 1 d before DOCA-salt treatment (A and B) or at the end of DOCA-salt treatment (C and D). Graphs representing MAP and HR over a 24-h period. Values are means ± se (n = 4).

Fig. 3.

Effect of NK-1R antagonists on renal glomerular injury of DOCA-salt-hypertensive mice. A, Histological sections stained with PAS stain showing glomerulosclerosis in control (a) and DOCA-salt-treated mice receiving vehicle (b), L-733,060 (c), or RP-67580 (d). The arrows indicate that areas of glomerulosclerosis. Magnification, ×400. B, Quantitative evaluation reveals that effect of L-733,060 and RP-67580 on glomerulosclerosis index in DOCA-salt-hypertensive mice. Values are means ± se (n = 6–8). *, P < 0.05 vs. control mice; †, P < 0.05 vs. DOCA-salt-treated mice.

Fig. 4.

Effect of NK-1R antagonists on renal cortical tubulointerstitial injury of DOCA-salt-hypertensive mice. A, Histological sections stained with Masson's trichrome stain showing renal cortical tubulointerstitial injury in control (a) and DOCA-salt-treated mice receiving vehicle (b), L-733,060 (c), or RP-67580 (d). The arrows indicate that tubular dilation and interstitial fibrosis. Magnification, ×200. B, Quantitative evaluation reveals that effect of L-733,060 and RP-67580 on tubulointerstitial injury score in DOCA-salt-hypertensive mice. Values are means ± se (n = 6–8). *, P < 0.05 vs. control mice; †, P < 0.05 vs. DOCA-salt-treated mice.

Fig. 5.

Effect of NK-1R antagonists on renal cortical interstitial monocyte/macrophage infiltration of DOCA-salt-hypertensive mice. A, Immunohistochemically stained sections showing that F4/80-positive cells (monocytes/macrophages in red) in renal cortex from control (a) and DOCA-salt-treated mice receiving vehicle (b), L-733,060 (c), or RP-67580 (d). The arrows indicate that F4/80-positive cells. Magnification, ×400. B, Quantitative evaluation reveals that effect of L-733,060 and RP-67580 on F4/80-positive cells in DOCA-salt-hypertensive mice. Values are means ± se (n = 6–8). *, P < 0.05 vs. control mice; †, P < 0.05 vs. DOCA-salt-treated mice.

Fig. 6.

Effect of NK-1R antagonists, including L-733,060 and RP-67580, on renal collagen levels in DOCA-salt-hypertensive mice. Values are means ± se (n = 6–8). *, P < 0.05 vs. control mice; †, P < 0.05 vs. DOCA-salt-treated mice.

Fig. 7.

Effect of DOCA-salt treatment on plasma SP level. Values are means ± se (n = 6–8). *, P < 0.05 vs. control mice.