Treatment with apocynin selectively restores hippocampal arteriole function and seizure-induced hyperemia in a model of preeclampsia

Abstract

Preeclampsia (PE) is a hypertensive disorder of pregnancy associated with neurovascular dysfunction, cognitive impairment and increased seizure susceptibility. Here, we sought to determine if treatment of experimental PE (ePE) rats with apocynin could prevent hippocampal arteriolar (HA) dysfunction and impaired seizure-induced hyperemia within the hippocampus, a brain region central to cognition and seizure generation. Isolated and pressurized HAs from Sprague Dawley rats that were normal pregnant (Preg; n = 8), ePE (n = 8) or ePE treated with apocynin for 2 weeks of gestation (ePE + apo; n = 8) were compared. Hippocampal blood flow (n = 6/group) was measured using hydrogen clearance before and during seizure. Aorta elastin was quantified using histochemistry. ePE was associated with HA dysfunction including reduced contraction to endothelin-1 and diminished dilation to the endothelium-dependent vasodilator NS309 that was prevented by apocynin. However, apocynin had no effect on ePE-induced impairment of dilation to the nitric oxide donor sodium nitroprusside, but increased myogenic tone and substantially increased HA distensibility. Seizure-induced hyperemia was impaired in ePE rats that was restored by apocynin. Aorta from ePE rats had reduced elastin content, suggesting large artery stiffness, that was unaffected by apocynin. Thus, while apocynin partially prevented HA dysfunction, its restoration of functional hyperemia may be protective of seizure-induced injury during eclampsia.

Keywords: Hippocampus; hippocampal arterioles; oxidative stress; preeclampsia; seizure-induced hyperemia.

Figure 1.

Active lumen diameters and myogenic tone of HAs from Preg, ePE and ePE + apo rats. (a) Lumen diameter of HAs over a wide range of pressures. There was no difference in lumen diameter between groups. (b) Myogenic tone of HAs from all groups. There was a significant increase in tone in HAs from ePE + apo animals compared to the other two groups at 40, 60 and 80 mmHg. Data are presented as mean ± SD; *p < 0.05 vs. Preg; ^p < 0.05 vs. ePE by one-way ANOVA and post hoc Bonferroni test for multiple comparisons.

Figure 2.

Concentration-response curves to ET-1, NS309 and SNP in HAs. (a) Percent constriction to ET-1. HAs from all groups of animals constricted in a dose-dependent manner to ET-1; however, HAs from ePE rats constricted less to lower concentrations of ET-1 than arterioles from Preg. Preg **p < 0.01 vs. Preg and ePE + apo; (b) Dilation to NS309. HAs from all groups dilated to NS309. Dilation was impaired in HAs from ePE rats compared to Preg. Treatment with apocynin restored the dilation to NS309 in HAs from ePE rats. *p < 0.05 and **p < 0.01 vs. Preg; ^p < 0.05 and ^^p < 0.01 vs. ePE+apo by one-way ANOVA and post hoc Bonferroni test for multiple comparisons. (c) Dilation of HAs to SNP was impaired in ePE compared to Preg that was not restored by apocynin. ^p < 0.05 vs. ePE+apo; *p < 0.05 vs. ePE by one-way ANOVA with posthoc Bonferroni test for multiple comparisons. Data are presented as mean ± SD.

Figure 3.

Passive structural and biomechanical properties of HAs from all groups. (a) Passive lumen diameters of HAs over a wide range of pressures. There was no difference in passive HA diameters between Preg and ePE; however, apocynin treatment significantly increased lumen diameter. *p < 0.05 vs. Preg and ePE groups by one-way ANOVA and post hoc Bonferroni test for multiple comparisons. (b) Wall thickness was not different between HAs from Preg and ePE but was significantly greater in ePE + apo HAs at pressures below 40 mmHg. **p < 0.01 vs. Preg and ePE groups. (c) Stress-strain curves of HAs from all groups. There was a leftward shift in the curve from ePE vs. Preg, suggesting increased vascular stiffness. However, treatment with apocynin shifted the curve to the right, demonstrating decreased vessel stiffness compared to both groups. Data are presented as mean ± SD.

Figure 4.

Changes in CBF in hippocampus from all groups at baseline and during seizure. (a–c) CBF measured by hydrogen clearance at baseline and during seizure in individual animals. CBF increased in Preg but decreased in ePE animals; apocynin treatment restored the hyperemic response to seizure, but was not as robust as in Preg animals. (d) Summary data showing the percent change in CBF in response to seizure calculated from baseline. **p < 0.01 vs. Preg and ePE + apo by one-way ANOVA with posthoc Bonferroni test for multiple comparisons. (e) Summary data showing absolute CBF in all groups both at baseline and in response to seizure. *p < 0.05 and **p < 0.01 vs. baseline by paired t-test. Data are presented as mean ± SD.

Figure 5.

Elastin content of aorta from all groups. (a) Representative photomicrographs of aortic cross-sections stained for elastin with VVG stain. The dark lamellae are prominent in medial layer. (b) Elastin content of aorta quantified by image analysis. There was a decrease in elastin content in aorta from ePE vs. Preg that was not restored by apocynin. *p < 0.05 vs. Preg by one-way ANOVA with posthoc Bonferroni test for multiple comparisons. Data are presented as mean ± SD.

Figure 6.

Serum levels of inflammatory markers. (a) There was a significant increase in serum levels of 8-isoprostane from ePE that was prevented by treatment with apocynin. *p < 0.05 vs. ePE by one-way ANOVA and Tukey’s test for multiple comparisons. (b) Serum levels of TNF-α were undetectable in Preg animals and increased in ePE. Apocynin treatment increased TNF-α in ePE + apo animals. **p < 0.05 vs. Preg by Dunnett’s test. Data are presented as mean ± SD.