Role of tyrosine kinase in dilator responses of rat basilar artery in vivo

Tyrosine phosphorylation modulates the vascular responses of mesenteric arteries from human colorectal tumors

The aim of this study was to analyze whether tyrosine phosphorylation in tumoral arteries may modulate their vascular response. To do this, mesenteric arteries supplying blood flow to colorectal tumors or to normal intestine were obtained during surgery and prepared for isometric tension recording in an organ bath. Increasing tyrosine phosphorylation with the phosphatase inhibitor, sodium orthovanadate produced arterial contraction which was lower in tumoral than in control arteries, whereas it reduced the contraction to noradrenaline in tumoral but not in control arteries and reduced the relaxation to bradykinin in control but not in tumoral arteries. Protein expression of VEGF-A and of the VEGF receptor FLT1 was similar in control and tumoral arteries, but expression of the VEGF receptor KDR was increased in tumoral compared with control arteries. This suggests that tyrosine phosphorylation may produce inhibition of the contraction in tumoral mesenteric arteries, which may increase blood flow to the tumor when tyrosine phosphorylation is increased by stimulation of VEGF receptors.

Valsartan improves the lower limit of cerebral autoregulation in rats

The effects of angiotensin II type 1 receptor blockers (ARBs) on cerebral blood flow (CBF) autoregulation have not been fully clarified. Thus, we examined the acute effect of valsartan, the most selective ARB, on CBF autoregulation in spontaneously hypertensive rats. Intravenous administration of valsartan (0.3 mg/kg) reduced the mean arterial pressure (MAP) from 184+/-5 (mean+/-SEM) to 174+/-5 mmHg (p<0.001) without affecting CBF as measured by laser-Doppler flowmetry. The lower limit of CBF autoregulation (the MAP at which the CBF was 80% of the baseline value) in the valsartan-treated group (122+/-3 mmHg) was significantly lower than that in the control group (135+/-4 mmHg, p<0.05). Reverse transcribed-polymerase chain reaction and immunohistochemical staining demonstrated that both angiotensin II type 2 receptors and angiotensin II type 1 receptors (AT1Rs) were expressed in endothelial and smooth muscle cells of the rat cerebral arteries. These results suggest that specific inhibition of AT1Rs in the cerebral circulation causes the leftward shift of the lower limit of autoregulation.

Endothelial influences on cerebrovascular tone

The cerebrovascular endothelium exerts a profound influence on cerebral vessels and cerebral blood flow. This review summarizes current knowledge of various dilator and constrictor mechanisms intrinsic to the cerebrovascular endothelium. The endothelium contributes to the resting tone of cerebral arteries and arterioles by tonically releasing nitric oxide (NO•). Dilations can occur by stimulated release of NO•, endothelium-derived hyperpolarization factor, or prostanoids. During pathological conditions, the dilator influence of the endothelium can turn to that of constriction by a variety of mechanisms, including decreased NO• bioavailability and release of endothelin-1. The endothelium may participate in neurovascular coupling by conducting local dilations to upstream arteries. Further study of the cerebrovascular endothelium is critical for understanding the pathogenesis of a number of pathological conditions, including stroke, traumatic brain injury, and subarachnoid hemorrhage.

The beneficial effects of protein tyrosine kinase inhibition on the circulatory failure induced by endotoxin in the rat

Implication of enhanced activity of tyrosine kinases has been established in the pathophysiology of many diseases associated with local (e.g., atherosclerosis) or systemic (e.g., septic shock) inflammation. The main objective of this study was to elucidate whether tyrosine kinase and nitric oxide were involved in endotoxin-induced impairment of vascular responses to sympathetic nerve stimulation (SNS) in rat isolated mesenteric bed. Therefore, the effects of genistein, an inhibitor of protein tyrosine kinase, and L-NAME (N-nitro-L-arginine methyl ester), an inhibitor of nitric oxide synthase, on endotoxin-induced shock were investigated in the thiopental-anesthetized rats. We also studied the effects of endotoxin on the vasoconstrictor responses to SNS in the rat isolated perfused mesenteric bed. Endotoxin injection (10 mg kg(-1), i.p.) produced a marked hypotension and a reduction of the pressor responses elicited by phenylephrine (0.1, 0.3, and 3 microg kg(-1), i.v.). Pretreatment of the rats with either genistein (10 mg kg(-1) i.p., 2 h before endotoxin injection), L-NAME (0.1 mg kg(-1), i.p., 30 min before endotoxin injection), or a combination of both attenuated the hypotension caused by endotoxin. SNS in the rat isolated perfused mesenteric bed caused a frequency-dependent vasoconstrictor response, which was abolished by tetrodotoxin (10(-7) M), prazoscin (10(-7) M), and guanethidine (10(-7)M). In mesenteric vascular beds removed from rats injected with endotoxin, the vasoconstrictor responses to SNS were markedly impaired. Although genistein and L-NAME pretreatment attenuated the vascular hyporeactivity to phenylephrine, they did not improve the impaired SNS response of the isolated vascular bed of endotoxin-treated animals. These results indicate that genistein and L-NAME pretreatment prevent the hypotension and the delayed hyporeactivity to phenylephrine induced by endotoxin, but they failed to restore the vascular hyporeactivity to SNS.

Chronic administration of a tyrosine kinase inhibitor restores functional and morphological changes of the basilar artery during chronic hypertension

OBJECTIVE

Activation of tyrosine kinase appears to play an important role in pathogenesis of cardiovascular disease during chronic hypertension. In the present study, we tested the hypothesis that long-term treatment with an inhibitor of tyrosine kinase would have beneficial effects on hypertension-induced morphological and functional changes of the cerebral artery.

METHODS

Male spontaneously hypertensive rats (SHR; 4 months old) were fed normal rat chow, or that containing an inhibitor of tyrosine kinase, genistein (1 mg/kg chow). Normotensive Wistar-Kyoto (WKY) rats were also fed either of the chows. After feeding the rats for 2 months, we measured wall thickness, diameter of the basilar artery and its dilator responses to acetylcholine (ACh); Y-26763, an opener of ATP-sensitive potassium channels; and Y-27632, an inhibitor of Rho-associated kinase.

RESULTS

Treatment with genistein did not cause significant changes in physiological variables, including mean arterial pressure in either strain. In control SHR, the wall thickness of the basilar artery was greater than that of WKY rats. Genistein treatment reduced the wall thickness significantly in SHR. Vasodilator responses induced by ACh and Y-26763 were markedly attenuated in SHR compared to WKY rats, and treatment of SHR with genistein significantly improved the vasodilatation. Dilatation of the artery in response to Y-27632 was enhanced in SHR compared to WKY rats and treatment of SHR with genistein did not affect the enhanced vasodilator responses to Y-27632.

CONCLUSIONS

Chronic treatment with genistein may be a novel approach to prevent cerebrovascular disorders.

Tumor necrosis factor-alpha impairs endothelium-dependent relaxation of rat renal arteries, independent of tyrosine kinase

We hypothesized that tumor necrosis factor-alpha (TNF-alpha) mimics endotoxin in attenuating endothelium-dependent vasodilation and smooth muscle constriction of rat renal arteries, and that tyrosine kinase is involved. Isolated rat renal arteries (n =6 per group), pretreated for 2 h by genistein (4',5,7-trihydroxyisoflavone, 10 microg/mL, a tyrosine kinase inhibitor) or vehicle, were exposed for 2 h to recombinant human (rh) TNF-alpha (100 ng/mL) or vehicle. rhTNF-alpha attenuated (P < 0.05) the constriction response to depolarizing 125 mM KCl (952.6+/-125.3 mg/mm vs. 1191.4+/-136.8 mg/mm in rhTNF-alpha-exposed and control segments, respectively), but did not affect the constriction response to norepinephrine (NE, 0.01-10 microM). Genistein did not affect the constriction response to KCl. The concentration-response relation to NE in genistein-pretreated control segments showed (P < 0.05) a rightward shift, while the maximum constriction was not affected. Genistein did not prevent a reduction (P < 0.05) by rhTNF-alpha in the maximum response to NE (721.7+/-42.4 mg/mm vs. 999.8+/-84.4 mg/mm in controls). The endothelium-dependent relaxation induced by (acetyl choline) ACh (0.001-1.0 microM) was attenuated (P < 0.05) by rhTNF-alpha (39.4%+/-6.7% and 77.4%+/-10.0% in rhTNF-alpha-exposed and control segments, respectively). The reduction (P < 0.05) in maximum ACh-induced relaxation after exposure to rhTNF-alpha was not affected by genistein (44.6%+/-3.4% and 70.8% x 2.2% in genistein-pretreated rhTNF-alpha-exposed and control segments, respectively). Hence, the attenuated endothelium-dependent relaxation and smooth muscle constriction of rat renal arteries following short-term rhTNF-alpha exposure, mimicking the effect of endotoxin, does not involve the activity of tyrosine kinase. The latter may be involved in pharmacomechanical coupling, by increasing Ca2+ sensitivity, but less in the electromechanical coupling of smooth muscle constriction.

Long-term effects of benidipine on cerebral vasoreactivity in hypertensive rats

We tested the hypothesis that long-term application of a Ca2+ channel blocker would ameliorate the functional and morphological deterioration of the cerebral arteries during hypertension. Male spontaneously hypertensive rats (SHR) were fed a standard rat chow, containing a low (3 mg/kg/day) or high dose (6 mg/kg/day) of benidipine, a Ca2+ channel blocker, for 2 months. Using a cranial window, we examined responses of the basilar artery to acetylcholine, sodium nitroprusside, (-)-(3S,4R)-4-(N-acetyl-N-hydroxyamino)-6-cyano-3,4-dihydro-2,2-dimethyl-2H-1-benzopyran-3-ol (Y-26763; an opener of ATP-sensitive K+ channels), and (R)-(+)-trans-N-(4-pyridyl)-4-(1-aminoethyl)-cyclohexanecarboxamide (Y-27632; an inhibitor of Rho-associated kinase). Mean arterial pressure of the control group was 193+/-5 mm Hg (mean+/-S.E.M.), while that of the low-dose benidipine group was 183+/-5 mm Hg and that of the high-dose group was 159+/-4 mm Hg. Dilator responses of the basilar artery to acetylcholine and Y-26763 were impaired in SHR compared with those of normotensive Wistar-Kyoto (WKY) rats and treatment with benidipine enhanced the vasodilator responses to acetylcholine and Y-26763 in SHR. Y-27632-induced dilatation of the basilar artery was enhanced in SHR compared to that in WKY rats and the vasodilatation was reduced by benidipine in SHR. Sodium nitroprusside caused similar dilatation of the basilar artery, in both WKY rats and the SHR control group, and benidipine did not affect nitroprusside-induced dilatation of the artery in SHR. The wall of the basilar artery was significantly thicker in SHR than in WKY rats and benidipine treatment reduced the wall thickness of the artery in SHR. These findings suggest that chronic treatment with a Ca2+ channel blocker may enhance the dilator capacity and reduce contractility of the basilar artery during hypertension. Benidipine may also ameliorate the morphological changes of the basilar artery in hypertension.

Role of mitogen-activated protein kinase pathway in acetylcholine-mediated in vitro relaxation of rat pulmonary artery

This study was designed to characterise the muscarinic receptor subtype responsible for acetylcholine-mediated in vitro pulmonary artery relaxation in rats and the importance of the presence of neostigmine (an anti-cholinesterase) during receptor characterisation. Cumulative administration of acetylcholine elicited concentration-dependent relaxation of phenylephrine (1 microM) precontracted preparations. Inclusion of neostigmine (10 microM) caused a parallel leftward shift with an increase of the pD(2) value (7.09 vs. 6.43) of the concentration-response curve of acetylcholine. The magnitude of maximum relaxation, however, was not affected. Using a range of conventional muscarinic receptor antagonists (atropine, pirenzepine, methoctramine, p-FHHSiD and tropicamide) and the highly selective Green Mamba muscarinic toxins (MT-3 and MT-7), it was found that muscarinic M(3) receptors are probably responsible for endothelium-dependent relaxation of the pulmonary artery upon acetylcholine challenge. Preincubation with N(G)-nitro-L-arginine methyl ester (L-NAME, 20 microM, a nitric oxide synthase inhibitor), but not N(G)-nitro-D-arginine methyl ester (D-NAME, 20 microM), abolished acetylcholine-elicited relaxation. Moreover, 6-anilino-5,8-quinolinedione (LY 83583, 1 microM) and methylene blue (1 microM) (both are guanylate cyclase inhibitors) markedly attenuated acetylcholine-elicited relaxation. However, the presence of indomethacin (3 microM, a cyclo-oxygenase inhibitor), (-)-perillic acid (30 microM, a p21(ras) blocker), 2-[2'-amino-3'-methoxy-phenyl]-oxana-phthalen-4-one (PD 98059) (10 microM, a p42/p44 mitogen-activated protein kinase inhibitor), 4-(4-fluorophenyl)-2-(4-methylsulfinylphenyl)-5-(4-pyridyl)1H-imidazole (SB 203580) (1 microM, a p38 mitogen-activated protein kinase blocker), wortmannin (500 nM, a phosphatidylinositol-3 kinase inhibitor) and genistein (10 microM, a tyrosine kinase blocker) failed to alter acetylcholine-provoked pulmonary arterial relaxation. These results suggest that acetylcholine caused pulmonary arterial relaxation through the activation of muscarinic M(3) receptors in the endothelium. Moreover, the p21(ras)/mitogen-activated protein kinase pathway seems to play no role in mediating acetylcholine-elicited relaxation.

Agonist-specific differences in mechanisms mediating eNOS-dependent pial arteriolar dilation in rats

Nitric oxide (NO), derived from the endothelial isoform of NO synthase (eNOS), is a vital mediator of cerebral vasodilation. In the present study, we addressed the issue of whether the mechanisms responsible for agonist-induced eNOS activation differ according to the specific receptor being stimulated. Thus we examined whether heat shock protein 90 (HSP90), phosphatidylinositol-3-kinase (PI3K), and tyrosine kinase participate in ACh- versus ADP-induced eNOS activation in cerebral arterioles in vivo. Pial arteriolar diameter changes in anesthetized male rats were measured during sequential applications of ACh and ADP in the absence and presence of the nonselective NOS inhibitor N(omega)-nitro-L-arginine methyl ester (L-NAME), the neuronal NOS (nNOS)-selective inhibitor ARR-17477, the HSP90 blocker 17-(allylamino)-17-demethoxygeldanamycin (AAG), the PI3K inhibitor wortmannin (Wort), or the tyrosine kinase blocker tyrphostin 47 (T-47). Only NOS inhibition with L-NAME (not ARR-17477) reduced ACh and ADP responses (by 65-75%), which suggests that all of the NO dependence in the vasodilating actions of those agonists derived from eNOS. Suffusions of AAG, Wort, and T-47 were accompanied by substantial reductions in ACh-induced dilations but no changes in the responses to ADP. These findings suggest that muscarinic (ACh) and purinergic (ADP) receptor-mediated eNOS activation in cerebral arterioles involve distinctly different signal transduction pathways.

Role of Na(+)/H(+) exchanger in dilator responses of rat basilar artery in vivo

We tested the hypothesis that activation of Na(+)/H(+) exchanger is involved in dilator responses of the basilar artery to endothelium-dependent vasodilators 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. Because N(G)-nitro-L-arginine, an inhibitor of nitric oxide synthase, almost abolished vasodilator responses to acetylcholine and bradykinin, vasodilatation produced by the agonists appears to be mediated primarily by nitric oxide. 5-N,N-Hexamethyleneamiloride, an inhibitor of Na(+)/H(+) exchanger, 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. FR183998, another inhibitor of Na(+)/H(+) exchanger, also attenuated acetylcholine-induced dilatation of the basilar artery without affecting vasodilatation in response to sodium nitroprusside. Monomethylamine hydrochloride, which produces intracellular alkalinization, enhanced acetylcholine-induced dilatation of the basilar artery in the presence of 5-N,N-hexamethyleneamiloride. These results suggest that intracellular alkalinization produced by activation of Na(+)/H(+) exchanger may enhance nitric oxide production in the basilar arterial endothelium and thereby contribute to dilator responses of the artery in vivo.

Estrogen restores postischemic pial microvascular dilation

Estrogen protects the brain from experimental cerebral ischemia, likely through both vascular and neuronal cellular mechanisms. The purpose of this study was to determine whether chronic estrogen treatment in males and repletion in ovariectomized (Ovx) females reverses abnormalities in pial arteriolar reactivity during reperfusion from global forebrain ischemia (4-vessel occlusion, 15 min) and whether the site of protection is vascular endothelium. Male and Ovx female rats were implanted with either placebo or a 25-microg 17 beta-estradiol pellet 10 days before ischemia. With the use of intravital microscopy, pial vessel dilation to ACh (10 microM) and S-nitroso-N-acetyl-penicillamine (SNAP; 1 microM) and vasoconstriction to serotonin (10 microM) was examined in situ at 30--60 min of reperfusion. Postischemic changes in vessel diameter were compared with preischemic values for each agent. Postischemic response to both ACh and SNAP was lost in males and Ovx females, but not in estrogen pellet-implanted males and estrogen-implanted Ovx females, suggesting that estrogen protects both endothelial and smooth muscle-mediated vasodilation. Ischemia blunted vessel constriction to serotonin regardless of treatment. These data demonstrate that estrogen acts as a vasoprotective agent within the cerebral circulation and can improve microvascular function under conditions of an acutely evolving ischemic pathology.

Role of heat shock protein 90 in bradykinin-stimulated endothelial nitric oxide release

Previously we described ENAP-1, a 90-kDa protein that is tyrosine-phosphorylated in endothelial cells in response to bradykinin (BK) stimulation and is associated with endothelial nitric oxide synthase (eNOS). Subsequently, other investigators demonstrated that eNOS interacts with heat shock protein 90 (Hsp90) following stimulation of endothelial cells with vascular endothelial growth factor (VEGF), histamine, or fluid shear stress. Therefore, we tested the hypotheses that ENAP-1 and Hsp90 are the same protein and that BK activation of eNOS is dependent on Hsp90. Immunoblotting of immunoprecipitated Hsp90 with anti-phosphotyrosine antibody shows that Hsp90 is tyrosine-phosphorylated in response to BK stimulation of bovine aortic endothelial cells (BAECs). Coimmunoprecipitation of Hsp90 with anti-eNOS antibody reveals a Hsp90-eNOS complex in endothelial cells under basal conditions that is increased following BK stimulation. Taken together with the tyrosine phosphorylation data, these data suggest that ENAP-1 is Hsp90. BK-stimulated nitric oxide (NO) release is completely blocked by pretreatment with geldanamycin, a specific inhibitor of Hsp90, illustrating the importance of the Hsp90-eNOS interaction. In vitro binding assays with Hsp90-glutathione-S-transferase fusion proteins show direct binding of eNOS with the middle domain (residues 259-615) of Hsp90.

Tyrosine kinase inhibitors modulate agonist-induced vasodilation in the hamster cheek pouch

The purpose of this study was to determine whether inhibitors of tyrosine kinase attenuate vasodilation elicited by endogenously elaborated and exogenously applied nitric oxide in the in situ peripheral microcirculation. Using intravital microscopy, we found that pretreatment with genistein (1.0 microM) and tyrphostin 25 (10.0 microM), two structurally unrelated tyrosine kinase inhibitors, significantly attenuated acetylcholine-, bradykinin- and nitroglycerin-induced dilation of second-order arterioles (51 +/- 1 microm) in the in situ hamster cheek pouch (P < 0.05). Both inhibitors nearly abrogated acetylcholine-induced responses but only partially blocked bradykinin- and nitroglycerin-induced vasodilation. Genistein and tyrphostin 25 alone had no significant effects on resting arteriolar diameter and on adenosine-induced vasodilation in the cheek pouch. On balance, these data indicate that tyrosine kinase inhibitors attenuate endogenously elaborated and exogenously applied nitric oxide-induced vasodilation in the in situ hamster cheek pouch. However, the extent of tyrosine kinase inhibitor-sensitive pathway involvement in this response appears to be agonist dependent.

Dissimilar mechanisms of Ca(2+) response to bradykinin in different types of juxtamedullary glomerular arterioles

Bradykinin (BK)-induced changes in intracellular calcium level ([Ca(2+)](i)) were studied on fura 2-loaded afferent (AA) and efferent glomerular arterioles (EA) microdissected from juxtamedullary renal cortex. A distinction was made between thin and muscular EA. In AA and both types of EA, BK increased [Ca(2+)](i) through activation of B(2) receptors located only on the endothelium. The responses were not affected by nifedipine (10(-6) M) and were smaller in a Ca(2+)-free medium, providing evidence that BK opens voltage-independent Ca(2+) channels and mobilizes intracellular Ca(2+). Thin EA differed from AA and muscular EA by a lower sensitivity to BK (EC(50) = 6.95 +/- 3.81 vs. 0.21 +/- 0.08 and 0.18 +/- 0.13 nM, respectively; P < 0.05), a higher maximal response (89 +/- 5 vs. 57 +/- 5 and 44 +/- 7 nM; P < 0.001), and a spontaneous return to basal Ca(2+) level, even in the presence of BK. Genistein (10(-4) M) and herbimycin A (25 x 10(-6) M), specific inhibitors of tyrosine kinases, inhibited the [Ca(2+)](i) responses exclusively in AA. Genistein reduced the peak and plateau phases of responses by 69 +/- 9 and 82 +/- 6%, respectively, in a medium with Ca(2+) and the peak by 48 +/- 9% in a Ca(2+)-free medium. Similar reductions were observed with herbimycin A. These results show that dissimilar signal transduction pathways are involved in BK effects on juxtamedullary arterioles and that a tyrosine kinase activity could participate in the regulation of BK effect on AA but not on EA.