Pentosan polysulfate treatment preserves renal autoregulation in ANG II-infused hypertensive rats via normalization of P2X1 receptor activation

Abstract

Inflammatory factors are elevated in animal and human subjects with hypertension and renal injury. We hypothesized that inflammation contributes to hypertension-induced renal injury by impairing autoregulation and microvascular reactivity to P2X(1) receptor activation. Studies were conducted in vitro using the blood-perfused juxtamedullary nephron preparation. Rats receiving ANG II (60 ng/min) infusion were treated with the anti-inflammatory agent pentosan polysulfate (PPS) for 14 days. The magnitude and progression of hypertension were similar in ANG II and ANG II+PPS-treated rats (169 ± 5 vs. 172 ± 2 mmHg). Afferent arterioles from control rats exhibited normal autoregulatory behavior with diameter decreasing from 18.4 ± 1.6 to 11.4 ± 1.7 μm when perfusion pressure was increased from 70 to 160 mmHg. In contrast, pressure-mediated vasoconstriction was markedly attenuated in ANG II-treated rats, and diameter remained essentially unchanged over the range of perfusion pressures. However, ANG II-treated rats receiving PPS exhibited normal autoregulatory behavior compared with ANG II alone rats. Arteriolar reactivity to ATP and β,γ-methylene ATP was significantly reduced in ANG II hypertensive rats compared with controls. Interestingly, PPS treatment preserved normal reactivity to P2 and P2X(1) receptor agonists despite the persistent hypertension. The maximal vasoconstriction was 79 ± 3 and 81 ± 2% of the control diameter for ATP and β,γ-methylene ATP, respectively, similar to responses in control rats. PPS treatment significantly reduced α-smooth muscle actin staining in afferent arterioles and plasma transforming growth factor-β1 concentration in ANG II-treated rats. In conclusion, PPS normalizes autoregulation without altering ANG II-induced hypertension, suggesting that inflammatory processes reduce P2X(1) receptor reactivity and thereby impair autoregulatory behavior in ANG II hypertensive rats.

Fig. 1.

Pentosan polysulfate (PPS) does not alter the progression of hypertension induced by chronic ANG II infusion. Systolic blood pressure (SBP) was measured by tail-cuff plethysmography (A) and telemetry (B) in control (circle), control+PPS (100 mg·kg⁻¹·day⁻¹, diamond), chronic ANG II infusion only (60 ng/min, triangles), or ANG II+PPS (squares) rats. PPS does not alter SBP in control or ANG II-infused rats. Values are means ± SE. Data presented from telemetry measurements reflect the average over a 24-h period.

Fig. 2.

PPS preserves autoregulatory behavior of afferent arterioles. A: changes in afferent arteriolar diameter in response to alterations in renal perfusion pressure were measured in control (circle), chronic ANG II infusion only (60 ng/min, triangle), or ANG II+PPS (square) rats. B: data are expressed as percentage of the control diameter at 100 mmHg. Values are means ± SE. The pressure-mediated vasoconstriction was normal in control+PPS kidneys. These data are presented in results, but the plot of these data was removed from Fig. 2 for clarity. *P < 0.05 vs. control diameter in same group. †P < 0.05 vs. control kidneys at the same perfusion pressure.

Fig. 3.

Afferent arteriolar response to superfusion of ATP. A: changes in afferent arteriolar diameter in response to superfusion of ATP were assessed in control (circle), chronic ANG II infusion only (60 ng/min, triangle), or ANG II+PPS (100 mg·kg⁻¹·day⁻¹, square) rats. B: data are expressed as percentage of the control diameter at 100 mmHg. Values are means ± SE. *P < 0.05 vs. control diameter in same group. †P < 0.05 vs. control kidneys at the same perfusion pressure.

Fig. 4.

Afferent arteriolar response to superfusion of β,γ-methylene ATP (mATP). A: changes in afferent arteriolar diameter in response to superfusion of β,γ-mATP were assessed in control (circle), chronic ANG II infusion only (60 ng/min, triangle), or ANG II+PPS (100 mg·kg⁻¹·day⁻¹, square) rats. B: data are expressed as percentage of the control diameter at 100 mmHg. Values are means ± SE. *P < 0.05 vs. control diameter in same group. †P < 0.05 vs. control kidneys at the same perfusion pressure.

Fig. 5.

Effect of PPS treatment on plasma transforming growth factor (TGF)-β1 concentration. The concentration of total biologically active TGF-β1 in plasma was measured by an ELISA. ANG II infusion significantly increased plasma TGF-β1 concentration (gray column). PPS (100 mg·kg⁻¹·day⁻¹, black column) treatment prevented elevation of plasma TGF-β1 concentration in ANG II rats, resulting in concentrations that were nearly identical to those of normotensive controls (white column). Values are expressed as means ± SE. †P < 0.05 vs. control rats. #P < 0.05 vs. ANG II rats.

Fig. 6.

Effect of PPS treatment on urinary albumin excretion. Urine (24 h) was collected on days 0, 6, and 12. Urinary albumin excretion increased progressively in ANG II-infused rats (60 ng/min, gray column) compared with control rats (white column). PPS (100 mg·kg⁻¹·day⁻¹, black column) treatment slowed the progression of albuminuria in ANG II rats, but it was still higher compared with control. Values are means ± SE. *P < 0.05 vs. day 0 in same group. †P < 0.05 vs. control rats in the same period of urine collection.

Fig. 7.

Score of α-smooth muscle actin (α-SMA) staining at afferent arterioles. Semiquantitative evaluation of α-SMA staining (A) revealed that immunostaining of α-SMA in afferent arterioles was significantly increased in ANG II-infused rats compared with that in control rats (P < 0.05), but markedly reduced by PPS (100 mg·kg⁻¹·day⁻¹) treatment to level similar to the control group (P > 0.05). Representative images (B–D) for immunostaining of α-SMA (brown) show strong arteriolar expression in ANG II-rats (C) in contrast to low expression in control (B) and ANG II+PPS (D) arterioles, respectively. Magnification ×40. Scale bars = 100 μm. Values are means ± SE. *P < 0.05 vs. control group. †P < 0.05 vs. ANG II group.