Abstract-We previously demonstrated that left ventricular hypertrophy (LVH) induced by angiotensin II infusion requires epidermal growth factor receptor (EGFR) activation to mediate the mitogen-activated protein kinase/extracellular signal-regulated kinase (MAPK/ERK) pathway. To test whether the EGFR-mediated MAPK/ERK activation plays an important role in development and maintenance of LVH in spontaneously hypertensive rats (SHR), we investigated the effects of antisense oligodeoxynucleotide to EGFR (EGFR-AS) on LVH and blood pressure in young and adult SHR. EGFR-AS, sense oligonucleotide to EGFR (EGFR-S; 1.5 mg/kg), or vehicle control (5% dextrose) with liposome was injected once a week for 2 months in 5-or 13-week-old SHR. The effect of EGFR-AS on the expression of EGFR and phosphorylated ERK in the heart were examined by Western blots. After treatment, EGFR-AS significantly (PϽ0.05) decreased left ventricular weight/body weight and blood pressure in young SHR compared with EGFR-S or control-treated rats. In adult SHR, EGFR-AS did not affect left ventricular weight/body weight and blood pressure. EGFR and phosphorylated ERK significantly declined from 5 to 20 weeks (PϽ0.05). EGFR-AS, but not EGFR-S, significantly (PϽ0.05) decreased the expression of EGFR and phosphorylated ERK in young SHR, but had no significant effect in adult SHR. These results suggests that EGFR-mediated ERK activation is critically important for LVH in young SHR. n patients with essential hypertension in which plasma renin activity is normal, ACE inhibitors or angiotensin (Ang) II type 1 receptor (AT1R) antagonists lower blood pressure (BP) and regress left ventricular hypertrophy (LVH). 1,2 This indicates the importance of the local renin angiotensin system in cardiovascular regulation and remodeling. Ang II promotes cell growth in vitro and induces LVH in rats without the elevation of BP. 3 The induction of cell growth by Ang II requires the activation of mitogen-activated protein kinase (MAPK) pathway through tyrosine kinase activation. 4 However, AT1R itself does not have a tyrosine kinase domain. We previously reported that the epidermal growth factor receptor (EGFR), which is a receptor-type tyrosine kinase, plays an important role in LVH in Ang II-infused hypertensive rats through the activation of extracellular signal-regulated kinase (ERK), one of the MAPK family members. 5 A greater reactivity of blood vessels 6 and enhanced mitogenic responses of aortic myocytes 4,7 to Ang II have been reported in spontaneously hypertensive rats (SHR). Ang II infusion increases EGFR mRNA 8 and protein in the aorta and heart. 5 EGFR protein levels are elevated in the kidney and aorta from genetically hypertensive rats. 9 The activities of ERKs in the heart were elevated in young SHR and decreased with age. 10,11 However, there is no direct evidence regarding the contribution of EGFR to ERK activation in the development and maintenance phase of hypertension and LVH in SHR. To address this question, we developed an effective antisense oligonucleot...

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Background and Purpose-The aromatic amino acid L-Phenylalanine (L-Phe) significantly and reversibly depresses excitatory glutamatergic synaptic transmission (GST) via a unique set of presynaptic and postsynaptic mechanisms. Therefore, we hypothesized that endogenous derivatives of L-Phe, which display potent antiglutamatergic activity, may safely and efficaciously protect the brain during conditions characterized by overactivation of glutamate receptors. Methods-We tested this hypothesis in vitro with a combination of patch-clamp and lactate dehydrogenase (LDH) analyses in rat cultured neurons exposed to simulated ischemia, and in vivo using a rat model of experimental stroke caused by transient middle cerebral artery occlusion (MCAO). Results-3,5-diiodo-L-tyrosine (DIT) and 3,5-dibromo-L-tyrosine (DBrT), endogenous halogenated derivatives of L-Phe, attenuated GST by similar mechanisms as L-Phe, but with greater potency. For example, the IC 50 s for DIT and DBrT to depress the frequency of alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA)/kainate receptormediated mEPSCs were 104.6Ϯ14.1 mol/L and 127.5Ϯ13.3 mol/L, respectively. Depression of GST by DIT and DBrT persisted during energy deprivation. Furthermore, DBrT significantly reduced LDH release in neuronal cultures exposed to oxygen glucose deprivation. In rats subjected to transient MCAO, DBrT decreased the brain infarct volume and neurological deficit score to 52.7Ϯ14.1% and 57.1Ϯ12.0% of control values, respectively. DBrT neither altered atrioventricular nodal and intraventricular conduction in isolated heart, nor heart rate and blood pressure in vivo. Conclusion-DBrT, an endogenous halogenated derivative of L-Phe, shows promise as a representative of a novel class of neuroprotective agents by exerting significant neuroprotection in both in vitro and in vivo models of brain ischemia.

We tested the hypothesis that dilator responses of the basilar artery to endothelium-dependent vasodilators are mediated by activation of tyrosine kinase in vivo. Using a cranial window in anesthetized rats, we examined responses of the basilar artery to acetylcholine and bradykinin. Topical application of acetylcholine and bradykinin increased diameter of the basilar artery in a concentration-related manner. Genistein, an inhibitor of tyrosine kinase, did not affect baseline diameter of the basilar artery but inhibited vasodilatation in response to acetylcholine and bradykinin, without affecting vasodilatation produced by sodium nitroprusside. Tyrphostin 47, another inhibitor of tyrosine kinase, attenuated acetylcholine-induced dilatation of the basilar artery without affecting vasodilatation in response to sodium nitroprusside. Tyrphostin 63, an inactive analogue of tyrphostin 47, did not affect acetylcholine-induced vasodilatation. Sodium orthovanadate, an inhibitor of tyrosine phosphatase, enhanced acetylcholine-induced dilatation of the basilar artery. These results suggest that dilator responses of the basilar artery to endothelium-dependent agonists, acetylcholine and bradykinin, are mediated in large part by activation of tyrosine kinase. Because vasodilatation produced by these agonists is mediated primarily by nitric oxide, activation of tyrosine kinase may have an important role in nitric oxide production in the basilar artery in vivo.

Background and Purpose-Serotonin is one of the most potent constrictors of cerebral blood vessels and is implicated in several pathological conditions, including migraine and cerebral ischemia. Recent evidence has suggested that tyrosine kinase is involved in vasocontractile responses. The objective of this study was to test the hypothesis that activation of tyrosine kinase contributes to serotonin-induced constriction of the basilar artery in vivo. Methods-Using a cranial window in anesthetized Sprague-Dawley rats, we examined effects of inhibitors of tyrosine kinase and tyrosine phosphatase on constrictor responses of the basilar artery to serotonin in vivo. Results-Serotonin (10 Ϫ8 , 10 Ϫ7 , and 10 Ϫ6 mol/L) produced constriction of the basilar artery by 12Ϯ2%, 27Ϯ2%, and 37Ϯ3%, respectively. Genistein (3ϫ10 Ϫ6 mol/L), an inhibitor of tyrosine kinase, did not affect baseline diameter of the basilar artery but attenuated serotonin-induced vasoconstriction (PϽ.05 versus control responses). Daidzein, an inactive analogue of genistein, did not affect serotonin-induced constriction of the basilar artery. Tyrphostin 47 (10 Ϫ5 mol/L), another inhibitor of tyrosine kinase, also attenuated serotonin-induced vasoconstriction, and tyrphostin 63, an inactive analogue of tyrphostin 47, did not affect the vasoconstriction. Sodium orthovanadate (10 Ϫ5 mol/L), an inhibitor of tyrosine phosphatase, enhanced serotonin-induced vasoconstriction. Phorbol 12,13-dibutyrate, a direct activator of protein kinase C, also caused constriction of the basilar artery, which was not affected by genistein or sodium orthovanadate. Conclusions-These results suggest that serotonin-induced constriction of the basilar artery is mediated, at least in part, by activation of tyrosine kinase in vivo. (Stroke. 1998;29:494-498.)