Changes in vascular reactivity following administration of isoproterenol for 1 week: a role for endothelial modulation

Abstract

1 The aim of this study was to assess the effects of treatment with isoproterenol (ISO, 0.3 mg kg À1 day À1 , s.c.) for 7 days on the vascular reactivity of rat-isolated aortic rings. Additionally, potential mechanisms underlying the changes that involved the endothelial modulation of contractility were investigated. 2 Treatment with ISO induced cardiac hypertrophy without changes in haemodynamic parameters. Aortic rings from ISO-treated rats showed an increase in the contraction response to phenylephrine (PHE) and serotonin, but did not change relaxations produced by acetylcholine or isoproterenol. Removal of the endothelium increased the responses to PHE in both groups. However, this procedure was less effective in ISO-treated as compared with control rats. Endothelial cell removal abolished the increase in the response to PHE in ISO-treated rats. The presence of N o -nitro-L-arginine methyl ester shifted the concentration-response curve to PHE to the left in both groups of rats. However, this effect was more pronounced in the ISO group. In addition, aminoguanidine (50 mM) potentiated the actions of PHE only in the ISO group. ISO treatment increased nitric oxide synthase (NOS) activity and neuronal NOS and endothelial NOS protein expression in the aorta. 3 Neither losartan (10 mM) nor indomethacin (10 mM) abolished the effects of ISO on the actions of PHE. Superoxide dismutase (SOD, 150 U ml À1 ) and L-arginine (5 mM), but neither catalase (300 U ml À1 ) nor apocynin (100 mM), blocked the effect of ISO treatment. In addition, we observed an increase in superoxide anion levels as measured by ethidium bromide fluorescence and of copper and zinc superoxide dismutase protein expression in ISO-treated rats. 4 In conclusion, our data suggest that ISO treatment alters the endothelial cell-mediated modulation of the contraction to PHE in rat aorta. The increased maximal response of PHE seems to be due to an increase in superoxide anion generation, which inactivates some of the basal NO produced and counteracts NO-mediated negative modulation even in the presence of high NO production and antioxidant defence.

Endothelial dysfunction in cardiovascular and endocrine-metabolic diseases: an update

“…However, it has been demonstrated that overexpression of eNOS could paradoxically be maladaptive by leading www.bjournal.com.br Braz J Med Biol Res 44 (9) 2011 to oxidative stress through synthesis of superoxide anion (19). In agreement with this hypothesis, we demonstrated that aortas from isoproterenol-treated animals present an increased activity and protein expression of eNOS and nNOS; in addition, L-arginine supplementation was able to normalize the hyperreactivity to phenylephrine (31). Thus, sustained β-adrenoceptor activation could exacerbate eNOS activity and expression, but, in turn, cause eNOS uncoupling that would become a source of superoxide anion production ( Figure 4).…”

“…The administration of isoproterenol, a non-selective β-adrenoceptor agonist, to laboratory animals for several days is used as a model of prolonged β-adrenoceptor stimulation. In the vasculature of these animals, we demonstrated that isoproterenol treatment increases the vasoconstrictor response to the α 1 -adrenoceptor agonist phenylephrine as well as to the serotonin (5-HT) agonist in rat (31) and mouse ( Figure 3A) aorta, although no changes in acetylcholine-induced relaxation were observed (31,32). In addition, endothelial removal and L-NAME incubation normalized the hyperreactivity to phenylephrine observed in aortas from isoproterenol-treated rats, indicating that persistent activation of β-adrenoceptors impairs basal endothelial-derived NO (31,32).…”

“…The reduction of basal NO availability induced by isoproterenol was not related to a reduction in eNOS activity. Indeed, eNOS activity and protein expression were found to be significantly enhanced in aortas from isoproterenol-treated rats (31). However, chronic isoproterenol treatment enhanced superoxide anion levels, measured by hydroethydine fluorescence in situ in rat (31) and mouse aorta ( Figure 3B).…”

Alterações vasculares induzidas pelo tratamento crônico com Isoproterenol: Investigação dos subtipos de receptores b-adrenérgicos envolvidos e da possível geração de um processo inflamatório local.

“…Além do mais, Davel et al (2006) demonstraram, pela primeira vez, que o tratamento crônico com isoproterenol aumenta a resposta contrátil ao agonista α 1 -adrenérgico fenilefrina em aorta de ratos. Estes dados são corroborados por outros autores que demonstraram um aumento do efeito pressórico da fenilefrina, "in vivo", em ratos e camundongos tratados em longo prazo com isoproterenol (TRINDADE et al, 1992;GAVA et al, 2004), e, recentemente, por dados da literatura, que também observaram aumento da vasoconstrição induzida por fenilefrina em aorta de ratos tratados cronicamente com isoproterenol (FUKUDA et al, 2008;LUO et al, 2008;XU et al, 2008).…”

“…Ao mesmo tempo, este tratamento também induziu um aumento na produção do fator vasodilatador óxido nítrico (NO), via aumento da atividade e expressão protéica das isoformas neuronal e endotelial da sintase de óxido nítrico (nNOS e eNOS), que tende a contrabalancear o aumento da resposta contrátil da fenilefrina, mas tem sua biodisponibilidade diminuída ao ser degradado pelo ânion superóxido (DAVEL et al, 2006 No mesmo sentido dos achados em aorta de ratos tratados com isoproterenol, há trabalhos que correlacionam disfunção endotelial a um incremento da geração de ERDOs no tecido vascular em animais com insuficiência cardíaca, apesar de um concomitante aumento da expressão protéica da eNOS (BOULOUMIÉ et al, 1997;BAUERSACHS et al, 1999). Uma redução da biodisponibilidade do NO conseqüente a um prejuízo na sua síntese ou via aumento de degradação pelo ânion superóxido é um dos principais mecanismos associado à disfunção endotelial em várias doenças cardiovasculares (BAUERSACHS et al, 1999;D'USCIO et al, 2001;BROSNAN et al, 2002 …”