This is the first study demonstrating enhanced PDZ-RhoGEF/RhoA/Rho kinase signaling during hypertension at the level of resistance-sized arteries. This enhanced signaling leads to increased MLCP phosphorylation, resulting in vascular hyper-reactivity.

Abstract-Decreases in intrinsic NO cause cerebral vasospasms because of the dysregulation of cGMP formation by NO-mediated pathways. Because 5-cyclopropyl-2-{1-(2-fluorobenzyl)-1H-pyrazolo [3,4-b]pyridin-3-yl}pyrimidin-4-ylamine (BAY 41-2272) is a potent soluble guanylyl cyclase (sGC) stimulator in an NO-independent manner, this study aimed to investigate the mechanisms underlying the relaxant effects of BAY 41-2272 in the rat basilar artery. Key Words: nitric oxide Ⅲ cyclic GMP Ⅲ nitric oxide synthase N itric oxide (NO) derived from perivascular nerve fibers and endothelial cells acts as vasodilator for the smooth muscle in the wall of cerebral arteries and, hence, plays an essential role in the regulation of cerebral blood flow under physiological and pathological conditions. 1-3 Physiologically, NO is produced by NO synthase (NOS) present in the endothelium (eNOS) and nerves (nNOS) to maintain a basal cerebrovasodilator tone. Conversely, inhibitors of NOS constrict cerebral arteries in vitro 4,5 and decrease cerebral blood flow in vivo. 6,7 NO promotes relaxation of the vascular smooth muscle of cerebral arteries through stimulation of soluble guanylyl cyclase (sGC). 8 -10 The binding of NO to the heme portion of the enzyme results in cGMP accumulation, which causes smooth muscle relaxation via different mechanisms, including activation of K ϩ channels, desensitization of the contractile proteins, and reduction in intracellular Ca 2ϩ concentration. 11 Impairment of NO-mediated vasodilation accounts for the pathogenesis of cerebral vasospasm. 12,13 Indeed, an inappropriate activation of sGC has been linked to various pathological conditions affecting the cardiovascular system. 14 Although the administration of NO donors to rats with stroke causes brain cGMP levels to increase, induces cell genesis, and improves functional recovery, 15 there are certain disadvantages with NO donor-based therapies, such as the unpredictable pharmacokinetics of NO, development of tolerance, and peroxinitrite formation that can lead to protein S-nitrosylation, as well as tyrosine nitration. 16 -18 Therefore, compounds that activate sGC in an NO-independent manner represent a promising therapeutic strategy.The non-NO-based pyrazolopyridine 5-cyclopropyl-2-{1-(2-fluorobenzyl)-1H-pyrazolo [3,4-b]pyridin-3-yl}pyrimidin-4-ylamine (BAY 41-2272) represents a new therapeutic principle that directly stimulates sGC and increases the sensitivity of the enzyme to NO. 19 This is the primary mechanism through which BAY 41-2272 produces antiplatelet activity, strong decreases in blood pressure, and vasorelaxation. 19,20 This study was designed to identify the mechanisms involved in the relaxations of rat basilar artery induced by BAY 41-2272. We also sought to test the hypothesis that direct stimulation of sGC by BAY 41-2272 relaxes this vessel in a synergistic fashion with endogenous NO.