Abstract-Small-artery responses to vasoconstrictor agonists are important for vascular function. To investigate the signaling pathways involved in contraction, we studied the activation and regulation of p38 mitogen-activated protein kinases (p38MAPKs) and heat shock protein (HSP) kinase by endothelin and noradrenaline in rat mesenteric arteries. Both vasoconstrictors activated p38␣ and/or p38␤ but not p38␥ or p38␦, leading to increased HSP kinase activity. p38MAPK activation by noradrenaline was maximum between 2 and 10 minutes and was wholly dependent on calcium influx but insensitive to the tyrosine kinase inhibitor herbimycin A. In contrast, endothelin induced a biphasic response, with activation at 2 and 10 minutes. The early activity was wholly dependent on calcium influx and inhibited by herbimycin A. The later activity was only 50% calcium dependent, was insensitive to herbimycin A, but was 50% inhibited by genistein, a nonselective tyrosine kinase inhibitor. With both agonists, p38MAPK activity returned to basal by 30 minutes. SB203580, a p38MAPK inhibitor, blocked agonist-induced HSP kinase activity, and herbimycin A inhibited activation by endothelin but not by noradrenaline. In addition, SB203580 inhibited noradrenaline-induced contraction but had little effect on contraction to endothelin. These data show that vasoconstrictors use different upstream activators of p38MAPK in vascular tissue and that the p38MAPK pathway is selectively implicated in the contractile response to noradrenaline in small arteries. Key Words: vasoconstrictors Ⅲ vascular smooth muscle Ⅲ heat shock proteins Ⅲ signal transduction V ascular tone is an important determinant of peripheral resistance and blood pressure, and abnormalities in small-artery contractility contribute to pathological states such as vasospasm and hypertension. 1 The major mechanism of smooth muscle contraction is an increase in cytoplasmic calcium and phosphorylation of the regulatory light chains of myosin. However, there is considerable evidence indicating that vasoconstrictors activate multiple ancillary pathways that modulate the contractile response (see reviews 2,3 ). Among the many pathways activated, protein kinase C, 2 Rho family G proteins, 3,4 nonreceptor tyrosine kinases, 5 and extracellular signal-regulated kinases (ERK1/2) 2,6 have been shown to play a role in smooth muscle contraction. Recently, stressactivated protein kinases have also been implicated in sustained contraction through regulation of the phosphorylation of heat shock protein (HSP) 27. 7 HSP27 belongs to a family of small HSPs that includes HSP20, myotonic dystrophy kinase-binding proteins, and crystallins. 8 Increased phosphorylation of HSP27 has been reported in response to a variety of vasoconstrictors in smooth muscle, 9 -12 and inhibition of HSP27 phosphorylation or interference with its function reduces contraction. 9 HSPs may also play a role in vascular diseases such as hypertension. For instance, stress-induced hypertension in rats increased the expression and phos...

A t the level of the resistance artery, hypertension also brings about a thickening of the vascular wall and inward encroachment on the lumen. This has been reported as being attributable to hypertrophy or hyperplasia of vascular smooth muscle cells (VSMCs), but studies have appeared suggesting that growth is not apparent in arteries at this level of the circulation. 1 In addition, detailed structural and mechanical analyses have shown that eutrophic inward remodeling can narrow the vascular lumen without precipitating hypertrophy. 2,3 A small amount of hypertrophy may be observed, and in some pathological states, hypertrophy may supervene and is an adverse prognostic sign. 4 For the remainder of this section, we consider the reasons why resistance arteries respond to hypertension in this manner.To understand how hypertension produces the above nonhypertrophic changes in small arteries, one must look at the role of the resistance vasculature. At physiological pressures, these vessels typically exhibit a level of contraction (myogenic tone) independent of neurohormonal influences. This response enables blood vessels to constrict or dilate in response to changes in pressure. This process, known as the myogenic response, is only observed in smaller resistance arteries, which mediate autoregulation of blood flow and stabilize capillary pressure. 5 Hypertrophy is observed in vessels that do not possess myogenic tone, whereas, in smaller resistance arteries, an initial increase in pressure will bring about increased myogenic constriction, which, if prolonged, will lead to inward eutrophic remodeling and/or a reduced arterial distensibility. 6 This structural difference between large conduit and resistance arteries is apparent in many models of hypertension, for example, in a hypertensive model bought on by chronic NO synthase inhibition. 7 In addition, the magnitude and duration of an increase in intraluminal pressure plays a role in determining the remodeling process. 8 It has become evident that the extracellular matrix (ECM) integrin-cytoskeleton axis plays an essential role in the mechanosensory apparatus, which enables VSMCs to detect and respond to changes in intraluminar pressure, allowing eutrophic inward remodeling of resistance arteries in hypertension. Eutrophic Inward RemodelingInward eutrophic remodeling is a process of structural adaptation observed in most forms of hypertension, including the onset of hypertension and milder hypertensive states. 9 -11 However, a few animal models of hypertension, such as a model developing hypertension independent of the renin-angiotensin system (BPH-2 mice), show hypertrophy as the predominant structural change. 12 Inward eutrophic remodeling is a relatively fast functional adaptation observed after prolonged vasoconstriction and is thought to be an energetically favored mechanism to preserve a reduced lumen diameter for long periods. 13 The process is also the preferred physiological mechanism by which wall stress can be normalized while maintaining vasomotor tone. ...

Abstract-Human essential hypertension is characterized by eutrophic remodeling of small arteries, with little evidence of hypertrophy. Likewise, vessels of young hypertensive TGR(mRen2)27 animals have undergone similar structural alterations. The role of integrins in resistance arteries of TGR(mRen2)27 during the eutrophic-remodeling process was examined as blood pressure rose. Initially, 8 ␣ and 3 ␤ integrins were identified and levels of expression investigated using RT-PCR. As pressure increased and remodeling advanced, integrin expression profiles revealed that only ␣V was significantly raised. In conjunction, we confirmed elevated integrin ␣V protein levels in TGR(mRen2)27 rat arteries and localization to the media using immunofluorescence. ␤1 and ␤3, but not ␤5 integrin subunits were coprecipitated with integrin ␣V and are implicated in the eutrophic remodeling process. Administration of a peptide antagonist of ␣V␤3 abolished remodeling but enhanced growth, indicating that hypertrophy supervened as a response to hypertensioninduced increases in wall stress. We have established that the only upregulated integrin, the ␣V subunit of integrin ␣V␤3, has a crucial role in the hypertensive remodeling process of TGR(mRen2)27 rat resistance arteries. During hypertensive remodeling, functions of specific ␣V␤3-extracellular matrix interactions are likely to allow vascular smooth muscle cell-length autoregulation, which includes a migratory process, to maintain a narrowed lumen after a prolonged constricted state. A lthough the causes of high blood pressure may vary, sustained hypertension is associated with changes in cardiovascular structure. 1 These can be seen from the left ventricle down to the resistance vessels, and there is a strong relationship between left ventricular mass and small artery structure. 2,3 Resistance to blood flow is provided by arteries with an internal diameter (ID) of Յ300 m, 4 and in subcutaneous vessels, there is clear evidence for an increased media thickness:lumen diameter ratio in essential hypertension, which is proportional to the severity of the blood pressure. 1,5,6 Such findings appear to be representative of other vascular beds, with similar results being reported in the small intestine and the heart. 7,8 The nature of the structural change that is effected by hypertension is a rearrangement of the preexisting material in the vascular wall without a major hypertrophic response. 9 This has been termed eutrophic inward remodeling, which is initiated by vascular smooth muscle cell (VSMC)-length autoregulation. 10 Constriction causes shortening of VSMCs and a return to normal length after dissipation of the stimulus; however, prolonged constriction causes cells to increase in overlap. This functional adaptation to prolonged vasoconstriction is thought to occur because it is an energetically favored mechanism to preserve a reduced lumen diameter for long periods. 10 All models of hypertension appear to demonstrate eutrophic remodeling in small arteries, although to differing extents. ...