Abstract 2305: Endothelin-1 Alters Nitric Oxide-Dependent Cerebrovascular Responses by Modulating The Phosphorylation State of eNOS via Rho Kinase
Hypertension (HTN) alters vital homeostatic mechanisms regulating cerebral blood flow (CBF) and increases the risk of stroke and dementia. HTN exerts some of its damaging effects by counteracting the beneficial vascular actions of nitric oxide (NO). The potent vasoconstrictor endothelin-1 (ET1) has been implicated in the pathogenesis of HTN, but its role in the cerebrovascular effects of HTN is unknown. We examined whether ET1 disrupts CBF regulation. CBF (laser-Doppler flowmetry) was assessed in the somatosensory cortex in anesthetized male C57Bl/6 mice (n=5/group) equipped with a cranial window. ET1 (35 pmol/kg/min; i.v. for 45 min) increased mean arterial pressure from 72±4 to 99±6 mmHg (p<0.05), without reducing resting CBF (p>0.05). However, ET1 attenuated the CBF increase produced by neocortical application of the endothelium-dependent vasodilator acetylcholine (ACh; -37±1%; p<0.05) and by whisker stimulation (-31±1%; p<0.05), responses dependent on NO. The CBF response to adenosine was intact (p>0.05) indicating that ET1 did not act by compromising smooth muscle relaxation. The effects of ET1 were prevented by the ET type A (ETA) receptor antagonist BQ123 (1µM; p<0.05), by the Rho kinase (ROCK) inhibitor Y27632 (1 µM; p<0.05), but not by the ETB antagonist BQ788 (100nM; p>0.05). ET-1 did not affect the CBF increase produced by the NO donor SNAP and did not increase free radicals, suggesting that ET-1 did not act by reducing NO vasoactivity or bioavailability. However, in brain endothelial cell cultures ET1 (10-100nM) attenuated the NO production induced by ACh (-49±4% at 50nM; p<0.05), an effect blocked by BQ123 and Y27632. ET1 increased eNOS phosphorylation at Thr495, which inhibits eNOS, and reduced phosphorylation at Ser1177, which activates eNOS, effects blocked by Y27632. These findings, collectively, suggest that ET1 alters key regulatory mechanisms of the cerebral circulation by modulating the phosphorylation state of eNOS via ROCK. The resulting downregulation of eNOS activity is responsible for the neurovascular dysregulation induced by ET1. ETA receptors may be a valuable target to counteract the deleterious cerebrovascular actions of HTN.
- © 2012 by American Heart Association, Inc.