Introduction
Chronic arterial hypertension shifts the autoregulation curve of cerebral blood flow (CBF), increasing the risk of cerebrovascular events such as ischemic and hemorrhagic stroke. These acute events also cause fluctuations in CBF, contributing to ischemic/reperfusion damage. Therefore maintaining adequate flow is a priority for reducing damage from compromised cerebrovascular function. Recent work has demonstrated a role for protein kinase C (PKC) isozymes in mediating arterial tone. Additionally, we have previously shown that delivery of a deltaPKC-specific inhibitor peptide, deltaV1-1-TAT47-57 (deltaV1-1-TAT), reduces cerebral damage when delivered following stroke. We therefore sought to determine whether chronic delivery of deltaV1-1-TAT improves survival from stroke in a chronic hypertensive rat model, and whether protection in this model may be due to deltaPKC-mediated effects on CBF, both in hypertensive animals, and in a transient focal ischemia model.
Methods
Dahl salt-sensitive rats were fed 8% salt diet from 6 weeks old to induce systemic hypertension. Rats were treated continuously with deltaV1-1-TAT (n=16), TAT (n=21) or saline (n=22) between 11 and 15 weeks of age using a subcutaneously implanted osmotic pump (5 μL/hr, 1 mM). There was no change in average blood pressure by peptide treatment. Animals were monitored for signs of stroke, and cerebral infarctions were confirmed at death by histological examination. To examine the role of deltaPKC in modulating cerebrovascular activity, we determined the effect of acute treatment with deltaV1-1-TAT peptide on CBF in a normotensive rat model of transient focal ischemia, and in a chronic hypertension model. Acute stroke model; normotensive, male Sprague-Dawley rats underwent 2 hr MCA suture occlusion. Following ischemia CBF was monitored (n=9). Hypertensive rat model; CBF was measured at age 9 weeks, 3 weeks following salt diet onset (n=10). In both models, a burr hole was drilled 1 mm posterior and 6 mm lateral to bregma (corresponding to ischemic territory in the MCAo model). CBF was measured using laser Doppler. Following a baseline period of 20–30 minutes following reperfusion onset, TAT control peptide or deltaV1-1-TAT peptide was injected by intraperitoneal bolus (0.2 mg/kg), and CBF was monitored for an additional 20–30 minutes.
Results
Chronic treatment with deltaV1-1-TAT improved survival rate from stroke in the hypertensive rat model; 12.5% of deltaV1-1-treated rats, 38.1% of TAT-treated rats and 40.9% of saline-treated rats died from stroke by 15 weeks old (P<0.05 deltaV1-1-TAT vs. TAT or saline). We found that delivery of deltaV1-1-TAT increased CBF following transient ischemia by 18+/−8% (P<0.05), but did not alter flow in sham-treated non-ischemic animals. In hypertensive rats, however, CBF responses were variable following delivery of deltaV1-1-TAT peptide; 50% of animals showed an increase in flow (of these, CBF increased by 24+/−4%). The source of this variation is currently under investigation.
Conclusion
Chronic treatment with deltaV1-1-TAT improves stroke survival in a rat model of chronic hypertension. This may be due to a reduction in ischemic injury related to increased blood flow. In addition, an increase in CBF was observed following delivery of deltaPKC inhibitor in a stroke model in normotensive rats, suggesting that deltaPKC is involved in improving cerebral blood flow following stroke.