ABSTRACT. Endothelin (ET), derived from the endothelium of blood vessels, is a potent vasoactive peptide. Although it has been reported to be involved in cardiovascular diseases, such as hypertension, the mechanism by which ET evokes vasoconstriction is still unclear. On the other hand, p42/p44 mitogen-activated protein kinase (MAPK) and p38 MAPK are activated by a variety of growth factors and cellular stresses, respectively. However, the role of p42/p44 MAPK and p38 MAPK on the ET-1-induced vasoconstriction is not fully understood. This study was undertaken to determine whether p42/p44 MAPK and p38 MAPK participate in the regulation of vascular smooth muscle contraction by ET-1. The isometric vasoconstriction and intracellular Ca 2+ ([Ca 2+ ] i ) were simultaneously measured using CAF-100. Phosphorylation of myosin light chain (MLC) and p42/p44 MAPK, p38 MAPK were determined by Western blots. In rat thoracic aorta, ET-1 induced a sustained contraction. In contrast, [Ca 2+ ] i was decreased with time. Both PD98059, an inhibitor of p42/ p44 MAPK, and SB203580, an inhibitor of p38 MAPK, partially attenuated ET-1-induced contractions in concentration-dependent manners. ET-1 increased phosphorylation of both p42/p44 MAPK and p38 MAPK, and PD98059 and SB203580 completely decreased phosphorylation of p42/p44 MAPK and p38 MAPK in response to ET-1 stimulation, respectively. On the other hand, PD98059 and SB203580 did not affect MLC phosphorylation in response to ET-1 stimulation. These results indicate that p38 MAPK, as well as p42/ p44 MAPK, may partially regulate the ET-1-induced contraction through a MLC phosphorylation-independent pathway. KEY WORDS: endothelin, mitogen-activated protein kinase, vasoconstriction.J. Vet. Med. Sci. 65(2): 225-230, 2003 Endothelin (ET) is a potent vasoactive peptide particularly derived from the endothelium of blood vessels [38]. ET is composed of 21-amino acids, and is classified into ET-1, ET-2 and ET-3 according to their amino acid composition [19]. ET-1 is the major ET generated in the endothelium. ET acts via specific plasma membrane receptors. ET A and ET B receptors have distinctive characteristics for ET [1,32]. ET A and ET B receptors on smooth muscle induce contraction and stimulate proliferation and cell hypertrophy [6]. Endothelial ET B receptors stimulate the production of nitric oxide and prostacyclin [33]. ET is known to be involved in cardiovascular diseases, including hypertension, myocardial infarction, congestive heart failure, restenosis and atherosclerosis [24].Many studies have evaluated ET-induced vasoconstriction. ET-1 evokes a long-lasting contraction, slow in onset, of isolated arteries, veins and in microcirculatory vessels from experimental animals and humans [2,4,25,38]. The mechanism by which contractions are evoked by ET-1 in isolated vascular preparations is complicated. The increase in the sensitivity of the contractile apparatus to intracellular Ca 2+ ([Ca 2+ ] i ), as well as the increase of [Ca 2+ ] i concentration, may be involved in ET-1-...

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Abstract. We investigated whether p42 / p44 mitogen-activated protein kinase (MAPK) and / or p38 MAPK participates in the regulation of vascular smooth muscle contraction by endothelin-1 (ET-1) in Wistar-Kyoto rat (WKY) and spontaneously hypertensive rat (SHR). ET-1 (10 nM) induced a sustained contraction in WKY and SHR aortas. PD98059 (100 m M), an inhibitor of p42/ p44 MAPK kinase, partially attenuated the ET-1-induced contraction in WKY and SHR. However, SB203580 (10 m M), an inhibitor of p38 MAPK, relaxed the ET-1-induced contraction to the resting levels in SHR, but not in WKY. ET-1 (10 nM) increased phosphorylation of both p42 / p44 MAPK and p38 MAPK in WKY and SHR. However, in SHR, p38 MAPK phosphorylation in response to ET-1 stimulation was increased more than in WKY. PD98059 (100 m M) and SB203580 (10 m M) abolished the phosphorylation of p42 / p44 MAPK and p38 MAPK in response to ET-1 stimulation in WKY and SHR, respectively. On the other hand, SB203580 (10 mM) did not affect myosin light chain (MLC) phosphorylation in response to ET-1 (10 nM) stimulation in WKY and SHR. From these results, it is concluded that p42 / p44 MAPK and/ or p38 MAPK partially regulates the ET-1-induced vasoconstriction in WKY. However, p38 MAPK, rather than p42 / p44 MAPK, activation plays an important role for the maintenance of ET-1-induced vasoconstriction in SHR through a MLC phosphorylationindependent pathway.

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