RESUMEN
Pulsatile fluid shear stress and circumferential stretch are responsible for the axial alignment of vascular endothelial cells and their actin stress fibers in vivo. We studied the effect of cyclic alterations in axial stretch independent of flow on endothelial cytoskeletal organization in intact arteries and determined if functional alterations accompanied morphologic alterations. Rat renal arteries were axially stretched (20%, 0.5 Hz) around their in vivo lengths, for up to 4h. Actin stress fibers were examined by immunofluorescent staining. We found that cyclic axial stretching of intact vessels under normal transmural pressure in the absence of shear stress induces within a few hours realignment of endothelial actin stress fibers toward the circumferential direction. Concomitant with this morphologic alteration, the sensitivity (log(EC(50))) to the endothelium-dependent vasodilator (acetylcholine) was significantly decreased in the stretched vessels (after stretching -5.15+/-0.79 and before stretching -6.71+/-0.78, resp.), while there was no difference in sodium nitroprusside (SNP) sensitivity. There was no difference in sensitivity to both acetylcholine and SNP in time control vessels. Similar to cultured cells, endothelial cells in intact vessels subjected to cyclic stretching reorganize their actin filaments almost perpendicular to the stretching direction. Accompanying this morphological alteration is a loss of endothelium-dependent vasodilation but not of smooth muscle responsiveness.
Asunto(s)
Actinas/fisiología , Actinas/ultraestructura , Endotelio Vascular/citología , Endotelio Vascular/fisiología , Acetilcolina/farmacología , Animales , Presión Sanguínea/fisiología , Polaridad Celular/efectos de los fármacos , Polaridad Celular/fisiología , Células Cultivadas , Citoesqueleto/efectos de los fármacos , Citoesqueleto/fisiología , Citoesqueleto/ultraestructura , Endotelio Vascular/efectos de los fármacos , Mecanotransducción Celular/fisiología , Micromanipulación/métodos , Microesferas , Movimiento (Física) , Nitroprusiato/farmacología , Periodicidad , Estimulación Física/métodos , Proyectos Piloto , Arteria Radial/citología , Arteria Radial/efectos de los fármacos , Arteria Radial/fisiología , Ratas , Valores de Referencia , Estrés Mecánico , Vasodilatación/efectos de los fármacos , Vasodilatación/fisiologíaRESUMEN
Hypoxia triggers a mechanism that induces vasodilation in the whole heart but not necessarily in isolated coronary arteries. We therefore studied the role of cardiomyocytes (CM), smooth muscle cells (SMC), and endothelial cells (EC) in coronary responses to hypoxia (PO(2) of 5-10 mmHg). In an attempt to determine the factor(s) released in response to hypoxia, we inhibited the contribution of adenosine, ATP-sensitive K(+) channels, prostaglandins, and nitric oxide. Isolated rat septal artery segments without (-T) and with a layer of cardiac tissue (+T) were mounted in a double wire myograph, and constriction was induced. Hypoxia induced a decrease in isometric force of 21% and 61% in -T and +T segments, respectively (P < 0.05). EC removal increased the relaxation to hypoxia in -T segments to 33% but had the same effect in +T segments (61%). Only one of the inhibitors, the adenosine antagonist in +T segments, partially affected the relaxation due to hypoxia. The role of adenosine is thus limited and other mechanisms have to contribute. We conclude that hypoxia induces a relaxation of SMC that is augmented by the presence of CM and blunted by the endothelium. A single mediator does not induce those effects.
Asunto(s)
Vasos Coronarios/fisiopatología , Endotelio Vascular/fisiopatología , Corazón/fisiopatología , Hipoxia/fisiopatología , Músculo Liso Vascular/fisiopatología , Acetilcolina/farmacología , Animales , Ácido Araquidónico/farmacología , Vasos Coronarios/efectos de los fármacos , Endotelio Vascular/efectos de los fármacos , Gliburida/farmacología , Corazón/efectos de los fármacos , Técnicas In Vitro , Indometacina/farmacología , Masculino , Músculo Liso Vascular/efectos de los fármacos , Nitroarginina/farmacología , Ratas , Ratas Wistar , Temperatura , Vasoconstricción/efectos de los fármacos , Vasoconstricción/fisiologíaRESUMEN
We studied the amplitude and response time (RT; time to 50% of maximal response) of pulmonary vasoreactivity and investigated whether the characteristics of pulmonary vasoreactivity could be modulated by endothelium removal, nitric oxide (NO) synthase inhibition [N(G)-nitro-L-arginine (L-NNA)], RhoA activation [lysophosphatidic acid (LPA)] and Rho kinase inhibition (Y-27632). Slow acetylcholine-induced pulmonary vasodilation (262 +/- 5 s) was not due to the RT of endothelial NO release (45-55 s) and was always longer than RT in renal arteries (15 +/- 4 s). The rate-determining step is located in the smooth muscle cells. This was confirmed by the existing differences between the RT of the NO solution and KCl-induced renal and pulmonary vasoreactivity in endothelium-denuded arteries. We found that the pulmonary contractile amplitude increases and the RT decreases by L-NNA or LPA. In contrast, Y-27632 reduced the contractile amplitude and increased the RT in pulmonary arteries. These phenomena were dependent on the contractile stimulus (phenylephrine or KCl). In conclusion, slow pulmonary vasoreactivity is a smooth muscle cell characteristic that can be enhanced by RhoA and NO or endothelium removal. These effects were counteracted by Rho kinase inhibition. We show a role for RhoA/Rho kinase and NO in the modulation of pulmonary vascular reactivity.