RESUMO
- Flow-dependent dilation is a fundamental mechanism by which large arteries ensure appropriate blood supply to tissues. We investigated whether or not the vascular kallikrein-kinin system, especially tissue kallikrein (TK), contributes to flow-dependent dilation by comparing wild-type and TK-knockout mice in which the presence or absence of TK expression was verified. We examined in vitro changes in the outer diameter of perfused carotid arteries from TK(+/+) and TK(-/-) mice. In both groups, exogenous bradykinin caused a similar dilation that was abolished by the B(2) receptor antagonist HOE-140, as well as by the NO synthase inhibitor N:(omega)-nitro-L-arginine methyl ester. However, purified kininogen dilated only TK(+/+) arteries, demonstrating the essential role of TK in the vascular formation of kinins. In TK(+/+) arteries, increasing intraluminal flow caused a larger endothelium-dependent dilation than that seen in TK(-/-). In both strains the flow response was mediated by NO and by endothelium-derived hyperpolarizing factor, whereas in TK(-/-) vasoconstrictor prostanoids participated as well. HOE-140 impaired flow-dependent dilation in TK(+/+) arteries while showing no effect in TK(-/-). This compound reduced the flow response in TK(+/+) arteries to a level similar to that in TK(-/-). After NO synthase inhibition, HOE-140 no longer affected the response of TK(+/+). Impaired flow-dependent dilation was also observed in arteries from knockout mice lacking bradykinin B(2) receptors as compared with wild-type animals. This study demonstrates the active contribution of the vascular kallikrein-kinin system to one-third of the flow-dependent dilation response via activation of B(2) receptors coupled to endothelial NO release.
Assuntos
Bradicinina/análogos & derivados , Artérias Carótidas/fisiologia , Calicreínas Teciduais/genética , Vasodilatação/fisiologia , Acetilcolina/farmacologia , Animais , Velocidade do Fluxo Sanguíneo/fisiologia , Bradicinina/farmacologia , Artérias Carótidas/efeitos dos fármacos , DNA Complementar/genética , DNA Complementar/metabolismo , Diclofenaco/farmacologia , Endotélio Vascular/fisiologia , Feminino , Expressão Gênica , Genótipo , Masculino , Camundongos , Camundongos Endogâmicos C57BL , Camundongos Endogâmicos , Camundongos Knockout , NG-Nitroarginina Metil Éster/farmacologia , Nitroprussiato/farmacologia , Fenilefrina/farmacologia , Calicreínas Teciduais/metabolismo , Vasodilatação/efeitos dos fármacosRESUMO
Specific HKg immunostaining detected with antiserum against the light chain (LC) of HKg was restricted to SRIF neurons of the hypothalamic periventricular area projecting to median eminence (ME). Heavy chain (HC) immunoreactivity related to HKg and/or low molecular weight kininogen (LKg) was found in some other hypothalamic territories. Specific TKg was mainly associated with vasopressin in neurons of suprachiasmatic (SCN), supraoptic (SON) and paraventricular (PVN) nuclei. By direct RIA, hypothalamus was found to contain the highest level of TKg (10ng/mg protein) and after trypsin hydrolysis and HPLC separation of kinins, 10.3 pg BK and 7.3 pg T-kinin/mg protein.