Neuroprotective effect of paeoniflorin on cerebral ischemic rat by activating adenosine A1 receptor in a manner different from its classical agonists

Abstract

The effects of paeoniflorin (PF), a compound isolated from Paeony radix, on neurological impairment and histologically measured infarction volume following transient and permanent focal ischemia were examined in Sprague-Dawley rats. In transient ischemia model, rats were subjected to a 1.5-h occlusion of the middle cerebral artery (MCA). The administration of PF (2.5 and 5 mg kg(-1), s.c.) produced a dose-dependent decrease in both neurological impairment and the histologically measured infarction volume. Similar results were also obtained when PF (2.5, 5, and 10 mg kg(-1), s.c.) was given in permanent ischemia model. The neuroprotective effect of PF (10 mg kg(-1), s.c.) was abolished by pretreatment of DPCPX (0.25 mg kg(-1), s.c.), a selective adenosine A1 receptor (A1R) antagonist. PF (10, 40, and 160 mg kg(-1), i.v.) had no effect on mean arterial pressure (MAP) and heart rates (HR) in the conscious rat. Additionally, PF (10(-3) mol l(-1)) had no effect on noradrenaline- (NA-) or high K+ concentration-induced contractions of isolated rabbit primary artery. In competitive binding experiments, PF did not compete with the binding of [3H]DPCPX, but displaced the binding of [3H]NECA to the membrane preparation of rat cerebral cortex. This binding manner was distinguished from the classical A1R agonists. The results demonstrated that activation of A1R might be involved in PF-induced neuroprotection in cerebral ischemia in rat. However, PF had no 'well-known' cardiovascular side effects of classical A1R agonists. The results suggest that PF might have the potential therapeutic value as an anti-stroke drug.

Figure 1

Chemical structure of PF.

Figure 2

Effect of PF in transient MCA occlusion model. (a) The neurological impairment of ischemic damage. (b) The volume of ischemic damage. PF (2.5 and 5 mg kg⁻¹) was given twice s.c. Each column and vertical bar represents the mean±s.e.m. of results from eight rats. ^**P<0.01 compared with saline-treated animals (one-way ANOVA followed by Dunnett's post hoc comparison).

Figure 3

Effect of PF in the permanent MCA occlusion model. PF (2.5, 5 and 10 mg kg⁻¹) was given twice s.c. Each column and vertical bar represents the mean±s.e.m. of results from 8–10 rats. ^*P<0.05, ^**P<0.01 compared with saline-treated animals (one-way ANOVA followed by Dunnett's post hoc comparison). ^#P<0.05 compared with PF (10 mg kg⁻¹)-treated animals (Paired Student's t-test).

Figure 4

Effect of PF on MAP and HR in conscious rats. (a) MAP, (b) HR. PF (10, 40 and 160 mg kg⁻¹) was injected i.v. Each point and vertical bar represents the mean±s.e.m. of 8–9 rats. ^*P<0.05, ^**P<0.01 compared with saline-treated animals (one-way ANOVA followed by Dunnett's post hoc comparison).

Figure 5

Effect of PF on isolated rabbit primary artery preparation. (a) Effect of PF on NA-induced contraction. (b) Effect of PF on high K⁺ concentration-induced contraction. Each column and vertical bar represents the mean±s.e.m. of results from eight samples. ^**P<0.01 compared with control, respectively (Paired Student's t-test).

Figure 6

Competitive binding of PF with [³H]DPCPX and [³H]NECA. (a) Competitive binding of PF with [³H]DPCPX to cerebral cortical membrane. (b) Competitive binding of PF with [³H]NECA. Binding was performed as described in Methods. Data shown are triplicate samples with mean±s.e.m. from two experiments.