Presynaptic Prostaglandin E2EP1-Receptor Facilitation of Cerebral Nitrergic Neurogenic Vasodilation

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Abstract
Background and Purpose—Prostaglandin E2(PGE2) modulates autonomic transmission in the peripheral circulation. We investigated the role of endogenous PGE2and its presynaptic EP1receptor subtype in modulating the autonomic neurotransmission in cerebral vasculature.Methods—The standard in vitro tissue-bath technique was used for measuring changes in isolated porcine basilar arterial tone. Calcium imaging and nitric oxide estimation along with immunohistochemical analysis for cyclo-oxygenase-1, cyclo-oxygenase-2, EP1receptor, PGE synthase, and neuronal nitric oxide synthase were done in cultured sphenopalatine ganglia and basilar artery.Results—Selective EP1receptor antagonists (SC-19220 and SC-51322) inhibited relaxation of endothelium-denuded basilar arterial rings elicited by transmural nerve stimulation (2 and 8 Hz) without affecting that induced by nicotine or sodium nitroprusside (a nitric oxide donor). The SC-19220 inhibition of transmural nerve stimulation-elicited relaxation was blocked by cyclo-oxygenase inhibitors (salicylic acid and naproxen) but was not affected by guanethidine (a sympathetic neuronal blocker) or atropine. Perivascular cyclo-oxygenase-1- and cyclo-oxygenase-2-immunoreactive fibers were observed in basilar arteries. PGE synthase and EP1receptor immunoreactivities were coincident with neuronal nitric oxide synthase immunoreactivities in perivascular nerves of the basilar arteries and the sphenopalatine ganglia. ω-conotoxin (an N-type calcium channel blocker) significantly blocked transmural nerve stimulation-induced relaxation, which was further attenuated by SC-19220. In cultured sphenopalatine ganglia neurons, exogenous PGE2significantly increased calcium influx and diaminofluorescein fluorescence indicative of nitric oxide synthesis. Both responses were blocked by SC-19220.Conclusions—These results suggest that neuronal PGE2facilitates nitric oxide release from the cerebral perivascular parasympathetic nitrergic nerve terminals by increasing neuronal calcium influx through activation of presynaptic EP1receptors. PGE2may play an important role in regulating the nitrergic neurovascular transmission in the cerebral circulation.

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