Certain Histological and Chemical Responses of the Vascular Interface to Acutely Induced Mechanical Stress in the Aorta of the Dog

The purpose of this study is to quantify certain histologic and chemical responses of the intimal tissues in vivo to acutely induced mechanical stresses. Evans blue dye was given to tag serum albumin and an artificial fat emulsion was infused so that altered fluxes of either serum proteins or the artificial chylomicrons across the vascular interface into the intimal region could be detected. Special histologic and photodensimetric techniques were developed to estimate these fluxes as well as the architectural changes in the endothelial cell population. Architectural changes were quantified by doing endothelial cell counts to quantify the "normal" and "abnormal" endothelial cell population density as a function of stress exposure. The stress corresponding to the greatest rate of change of normal to abnormal cell forms is defined as the acute critical yield stress (τ c ) and was found to average < 420 dynes/cm 2 . Similarly the stress at which the greatest number of cells are being eroded is defined as the erosion stress (τ e ). The flux of Evans blue dye into the intima increased with pressure or wall strain, with shearing stress, and with increased turbulence. The flux of artificial chylomicrons into the intimal region never occurred in the presence of a normal endothelial cell population and was found to be most heavy in areas of total cellular erosion.