1989 Volume 17 Issue 4 Pages 553-570
The interstitial fluid of arterial tissue constitutes a milieu interior for the intimal smooth muscle cells. Atherosclerotic foam cells arise from these cells when they are exposed to a high concentration of interstitial LDL. However, the available data on the concentrations of interstitial lipoproteins including LDL in normal arteries is unequivocal.
In this study, the author has demonstrated the localization, form, and concentration of interstitial lipoproteins in terms of their apoproteins of A-I, A-II, B, C-II, C-III, and E in the normal intimas from 26 thoracic aortas and 19 pulmonary arteries of 45 autopsied cases (male 23, female 22, age 54±19).
The localization of apoproteins was observed in the normal Intima of thoracic aorta and pulmonary artery by immunofluorescence: apo B localized mainly around the cell in the intima and along the internal elastic lamina, while apo A-I and A-II grouped in an islet form deep in the media. Apo C-II, C-III and E were sparsely present both in the intima and media. SDS-gradient PAG electrophoresis revealed all serum apoprotein bands with a _mobility corresponding to the serum counterparts.
PAG disk electrophoresis showed that apoproteins were complexed with sudanophillic lipids in the interstitial fluid, and migrated in 3 bands of mobility corresponding to those of serum VLDL, LDL and HDL. Three dimensional form of recovered lipid-apoprotein complex was confirmed to be spheres of a diameter of about 500Å and 200Å by transmission and scanning electronmicroscopy.
The concentrations of interstitial lipoproteins were measured by SRID for both thoracic and pulmonary interstitial fluids. Apo A-I was 5.2mg/ dl in thoracic aorta, while 0.4mg/dl in pulmonary artery, A-II 1.4mg/dl vs. 0.9mg/dl, B 18.2mg/dl vs. 10.3mg/dl, C-II 0.2mg/dl vs. 0.2mg/dl, C-III 1.1mg/dl vs. 0.4mg/dl and E 2.1mg/dl vs. 0.6mg/ dl, respectively. The concentrations of apoproteins gained in wet tissue weight were converted to the unit of mg/dl by using factors for water content of thoracic aorta 77±10%, and for pulmonary artery 81±19%, and the volume of extracellular space as 52±10% and 68±11%, respectively.
These indicated that there exists a distinct difference in the concentrations of lipoproteins between serum and interstitial fluid of both thoracic and pulmonary intimas: interstitial LDL is 1/5 to 1/10 of serum counterpart, VLDL 1/5 to 1/7, and HDL 1/25 to 1/35, respectively. These lipoprotein levels maintained as a millieu interior by an endothelial barrier provides intimal cells with cholesterol necessary but sufficient for their cellular metabolism. The alteration in this milieu interior brings forth the accumulation of cholesterol in the cytoplasma of intimal cells, and leads to the formation of foam cells in the intima.