Diminution of angiotensin II-induced contraction of the abdominal aorta isolated from Watanabe heritable hyperlipidemic rabbits.

The purpose of this study was to investigate the changes in vasocontractile responses in atherosclerosis, using abdominal aortic strips isolated from Watanabe heritable hyperlipidemic (WHHL) rabbits and Japanese White (control) rabbits. The aortic strips from WHHL rabbits showed a significantly lower contractile response to angiotensin II than that in strips from control rabbits. The contractile responses to phenylephrine and 5-hydroxytryptamine were not different in WHHL and control groups. The contractile response to angiotensin II was higher in endothelium-denuded aortic strips than in endothelium-intact strips, but to a greater extent in the control group than in the WHHL group. The contractile response to angiotensin II in the absence of the endothelium was also lower in the WHHL group than in the control group. Pretreatment with N(G)-nitro-L-arginine significantly increased the contractile response to angiotensin II in the endothelium-intact aortic strips in both the WHHL and control groups, while pretreatment with diclofenac did not affects the aortic contractile response to angiotensin II. The contractile responses to angiotensin II in the presence of N(G)-nitro-L-arginine and diclofenac were lower in the WHHL group than in the control group. The contractile response to angiotensin II in the presence of PD123319 was also lower in the WHHL group than in the control group. Endothelium-dependent relaxation by acetylcholine occurred to the some extent in the WHHL and control groups. These results suggest that the WHHL rabbit abdominal aorta displays attenuated angiotensin II-induced contraction, mainly due to an abnormality in the angiotensin II-specific contractile pathway of the medial smooth muscle.

Mechanism of human urotensin II-induced contraction in rat aorta.

Urotensin II induced sustained contraction with an EC(50) value of 2.29 +/- 0.12 nM in rat aorta. Urotensin II (100 nM) transiently increased cytosolic Ca(2+) level ([Ca(2+)](i)), followed by a small sustained phase superimposed with rhythmic oscillatory change. In the presence of verapamil and La(3+), the [Ca(2+)](i) oscillation was completely inhibited, although a small transient increase in [Ca(2+)](i) remained. The urotensin II-induced contraction was also partially inhibited by verapamil and La(3+). Combined application of verapamil, La(3+), and thapsigargin completely inhibited the increase in [Ca(2+)](i) with only partial inhibition of the contraction elicited by urotensin II. Urotensin II increased myosin light chain (MLC) phosphorylation to a level greater than that induced by 72.7 mM KCl (high K(+)). Pretreatment with Go6983 (PKC inhibitor), U0126 (MEK inhibitor), or SB203580 (p38MARK inhibitor) partially inhibited the urotensin II-induced contraction with no effects on the high K(+)-induced contractions. Wortmannin (MLC kinase inhibitor) only partially inhibited urotensin II-induced contraction, although it completely inhibited the high K(+)-induced contraction. These results suggest that urotensin II-induced contraction is mediated by the Ca(2+)/calmodulin/MLC kinase system and modulated by the Ca(2+) sensitization mechanisms to increase MLC phosphorylation. In addition, activations of PKC, p38MAPK, and ERK1/2 modulate the contractility mediated by urotensin II in rat aorta.

Chronic hypertriglyceridemia in young watanabe heritable hyperlipidemic rabbits impairs endothelial and medial smooth muscle function.

Several studies have suggested that hypertriglyceridemia is a common risk factor for coronary heart disease. Although increasing serum levels of triglyceride correlate with hypercoagulability, little is known about the contribution of hypertriglyceridemia to vascular function. We successfully segregated two lines of rabbits with genetically-determined severely high (TGH; 2764 +/- 413 mg/dl) and moderately high (TGL; 191 +/- 12 mg/dl) levels of triglyceride, but with comparable levels of total cholesterol, from Watanabe heritable hyperlipidemic rabbits. To determine whether hypertriglyceridemia was involved in alterations of vascular function, we conducted isometric tension studies and analyzed protein expression on thoracic aortic rings isolated from young (3-4 month) TGH, TGL and Japanese White rabbit (JW). No difference in percentage of plaque area in the thoracic aorta was found between TGH and TGL. Relaxing responses, evoked by sodium nitroprusside were similar in JW, TGL and TGH, but endothelium-dependent relaxation to acetylcholine was impaired in TGH compared with JW or TGL (maximal relaxation in JW; 83.5 +/- 2.7%, TGL; 79.9 +/- 5.3%, TGH; 59.1 +/- 5.7%, p<0.05). Relaxation to A23187 was also attenuated in TGH compared with JW, but not significantly different between TGL and JW. Endothelium-independent relaxation elicited by isoproterenol in TGH was significantly decreased compared with JW or TGL (maximal relaxation in JW; 95.2 +/- 2.6% TGL; 91.0 +/- 4.9%, TGH; 75.1 +/- 5.2%, p<0.05). Protein expression of angiotensin II type-1 receptor was increased in TGH and that of nitric oxide synthases-3 was attenuated in TGH compared with TGL. This is the first study showing that endothelium-dependent and -independent vascular relaxation under the condition of combined hyperlipidemia was severely impaired as compared to that under only hypercholesterolemia. These results suggest that hypertriglyceridemia aggravates functional impairment induced by hypercholesterolemia in endothelial and smooth muscle cells.

Difference in signal transduction mechanisms involved in 5-hydroxytryptamine- and U46619-induced vasoconstrictions.

In order to elucidate the signal transduction pathways of vascular smooth muscle contractions induced by stimulation of receptors for 5-hydroxytryptamine (5-HT) and thromboxane A2 (TXA2), both of which are released from activated platelets, we examined whether protein kinases, such as tyrosine kinase, p38 mitogen-activated protein kinase (MAPK) and protein kinase C (PKC), are involved in the contraction produced by either 5-HT or U46619 (an analog of TXA2) in the rat aorta. Both 5-HT and U46619 induced sustained contractions, which were markedly reduced in the absence of extracellular Ca2+. Verapamil (a L-type Ca2+ channel blocker) markedly inhibited the contractile response to 5-HT, while the U46619-induced contraction was only slightly inhibited by verapamil. Both contractile responses to 5-HT and U46619 were significantly inhibited by calphostin C (a PKC inhibitor). On the other hand, both genistein (5 microM, a tyrosine kinase inhibitor) and SB203580 (a p38 MAPK inhibitor) significantly inhibited 5-HT-induced contractions but had little effects on the contractions induced by U46619. These results suggest that the signal transduction mechanisms involved in the contractions mediated via 5-HT and TXA2 receptors are different as follows. Both the tyrosine kinase and p38 MAPK pathways are involved in 5-HT contraction but not in TXA2 contraction, while both contractions are strongly dependent on transplasmalemmal Ca2+ entry. The contractile responses to both 5-HT and TXA2 involve voltage-dependent Ca2+ channels and PKC.

Involvement of p44/42 mitogen-activated protein kinases in regulating angiotensin II- and endothelin-1-induced contraction of rat thoracic aorta.

In order to elucidate the signal transduction pathway of vascular smooth muscle contraction induced by the activation of receptors for angiotensin II and endothelin-1, we examined whether tyrosine kinases and mitogen-activated protein (MAP) kinases are involved in the development of force of contraction in the rat aorta. Isolated aortic smooth muscles without endothelium were incubated in a modified Krebs-Henseleit solution and stimulated with angiotensin II (100 nM) or endothelin-1 (10 nM). A tyrosine kinase inhibitor genistein (10 microM) reduced the angiotensin II- and endothelin-1-induced aortic contraction, while 10 microM of daidzein (an inactive analogue of genistein) did not. The K(+) depolarization-induced contraction was not attenuated by 10 microM of genistein. Selective inhibitors of MAP kinase/extracellular signal-regulated kinase (Erk) kinase (MEK) such as PD98059 [2-(2-amino-3-methoxyphenyl)-4H-1-benzopyran-4-one] and U0126 [1,4-diamino-2,3-dicyano-1,4-bis(2-aminophenylthio)butadiene] inhibited the angiotensin II- and endothelin-1-induced vasocontraction. The p44/42 MAP kinases were phosphorylated in cultured aortic smooth muscle cells and in physiologically contracted aortic vessels stimulated with angiotensin II and endothelin-1 for 5 min. The angiotensin II- and endothelin-1-induced phosphorylations of p44/42 MAP kinases were inhibited by PD98059 as well as U0126 in the intact aorta. These results suggest that the activation of genistein-sensitive tyrosine kinases and p44/42 MAP kinases is involved in the angiotensin II- and endothelin-1-induced rat aortic contraction.