title: [The vascular smooth muscle of great arteries: local control site of arterial buffering function?].
abstract: OBJECTIVE
  To characterize the viscoelastic properties of the aorta and pulmonary arteries and the effects of vascular smooth muscle activation on arterial buffering function.
  
  
  METHODS
  Aortic and pulmonary artery pressure and diameter were measured in six anesthetized sheep under baseline conditions, and during arterial hypertension induced by mechanical vascular occlusion (passive), and i.v. phenylephrine (active). Arterial wall elasticity and viscosity were calculated, and buffering function was characterized: a) locally as the viscosity/elasticity ratio, and b) globally for each circuit, as the time-constant of ventricular relaxation.
  
  
  RESULTS
  Viscoelasticity was higher in the aorta than in the pulmonary artery (p < 0.05), however, parietal buffering function was similar in both. Global buffering function was highest in the systemic circuit (p < 0.05). During passive hypertension, elasticity was significantly increased with no change in viscosity; this led to a significant reduction in local buffering function, and in global buffering function in each circuit. During active hypertension, viscosity increased (p < 0.05), while local and global buffering functions returned to baseline values.
  
  
  CONCLUSIONS
  The viscosity/elasticity ratio was higher in the aorta than in the pulmonary artery, and arterial wall buffering function was similar in both vessels. Systemic global buffering function was higher than pulmonary circuit buffering function. Elasticity depends on intravascular pressure, whereas viscosity is a marker of the degree of smooth muscle activation. Smooth muscle activation may benefit the cardiovascular system by maintaining local and global buffering functions.
authors.affiliation: Departamento de Fisiología. Facultad de Medicina. Universidad de la República. Montevideo. Uruguay. dbia@fmed.edu.uy
authors.forename: Daniel
authors.initials: D
authors.lastname: Bia
authors.forename: Ricardo L
authors.initials: RL
authors.lastname: Armentano
authors.forename: Juan C
authors.initials: JC
authors.lastname: Grignola
authors.forename: Damián
authors.initials: D
authors.lastname: Craiem
authors.forename: Yanina A
authors.initials: YA
authors.lastname: Zócalo
authors.forename: Fernando F
authors.initials: FF
authors.lastname: Ginés
authors.forename: Jaime
authors.initials: J
authors.lastname: Levenson
mesh_terms: D000818:Animals; D001013:Aorta, Thoracic / Q000502:physiology*; D001696:Biomechanical Phenomena; D004548:Elasticity; D009131:Muscle, Smooth, Vascular / Q000502:physiology*; D011651:Pulmonary Artery / Q000502:physiology*; D012756:Sheep