Hemodynamic forces are involved in the regulation of arterial structure and pathology, especially in atherogenesis. In this study our aims was to quantifying the changes of endothelium induced by modified blood shear.
In 12 rabbits, a one centimeter length stenotic collar was positioned around abdominal aorta. This procedure induced high pressure in antestenotic segment (AS), high velocity, high shear stress and low hydrostatic pressure in stenotic segment (SS) and low, turbulent shear stress and low hydrostatic pressure in poststenotic segment (PS). Four rabbits were used for control. Cytological examination was performed in aorta from rabbits sacrificed at 10 days (2 cases), 12 days (2 cases), 15 days (2 cases) and 35 days (3 cases). The endothelial morphology was quantified by nuclear measurement in frozen, Wright stained, smears. Crocker's method was used for AgNORs staining. Transmission electron microscopy was performed in 5 rabbits sacrificed at 25 days.
In first 10-15 days, the ECs from AS showed increased nuclear elongation but decreased nuclear area and higher number of AgNORs. At 35 days these changes regress, because of collaterals (mesenteric and lumbar arteries). In first 10-15 days, the ECs from SS showed elevated nuclear area. At 35 days the nuclear elongation was increased but the nuclear area was decreased. The number of AgNORs has similar values than in the control aorta. In first 10-15 days the nuclear elongation was intensely decreased into PS but at 35 days nuclear area was high increased and nuclear elongation have similar values with control aorta. The AgNORs number was elevated in 10-15 days but lowered at 35 days. In TEM, modified blood flow was correlated with endothelial changes. In AS, the ECs showed dilatation of rough endoplasmic reticulum and lipid vacuoles, intima was edematous with smooth muscular cells (SMCs) in synthetic phenotype. In SS, the ECs showed cubic morphology, few or absent interdigitating junctions and vacuolization RER and mitochondria. The SMCs from intima has synthetic and proliferative phenotype. In PS, the intercellular junctions showed vacuolization and few interdigitating processes. Disjunction of ECs from basal membrane was done by collagen fibers and SMCs cytoplasmic processes.
In conclusion, pulsatile flow and high pressure were associated with longer, larger, proliferative and vacuolated ECs, high shear stress combined with low pressure were associated with cubic and smaller ECs. Turbulent blood flow was associated with increased nuclear area, altered intercellular junctions and disjunction ECs-basal membrane. The increased ECs turn-over was associated with decreasing shear stress and turbulent flow.