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An in vitro preparation of rabbit aortic "intima-media" previously shown to exhibit stable rates of respiration and glucose metabolism and the high rate of aerobic glycolysis considered characteristic of the metabolism of this tissue was subjected to electron microscopic examination. In samples examined immediately after the aortae were dissected free of adipose tissue and adventitia, under conditions similar to those now in common use, marked and widespread alterations in endothelial cell structure were present, including loss of cell integrity. The vascular smooth muscle cells retained a normal electron microscopic (EM) appearance. During subsequent incubation with 5 mM glucose in Krebs-Ringer bicarbonate (KRB), pH 7.4, under the conditions usually employed in studies of this preparation, large zones of the luminal surface were rapidly denuded of endothelium, and the remaining endothelial cells exhibited a wide range of ultrastructural alterations. The smooth muscle cells, however, continued to maintain a normal EM appearance. A method was developed to prepare segments of rabbit aortic intima-media which retained an intact layer of endothelium resembling that observed in tissue fixed in situ. During a 1-h incubation with 5 mM glucose in KRB, pH 7.4, gas phase 5% CO2/95% O2, containing 6% bovine serum albumin, the intact aortic intima-media preparation retains an essentially unmodified EM appearance and exhibits linear rates of respiration. Under these conditions the intact aortic intima-media preparation exhibits significantly higher rates of O2 uptake and glucose uptake than those observed in our previous preparation or in other reported aortic intima-media preparations. The intact aortic intima-media does not exhibit the high rate of aerobic glycolysis during in vitro incubation that has been considered characteristic of the metabolism of rabbit, rat, and swine aortic intima-media. In addition, the magnitude of the Pasteur effect was far greater than that observed in other aortic intima-media preparations. The data suggest that component cells of the aortic intima-media may derive a major fraction of their energy requirements from respiration; they raise further questions concerning the significance of the high rate of aerobic glycolysis observed when aortic intima-media preparations are incubated in vitro, and they suggest that documentation of the EM appearance of the endothelium in such preparations is desirable.

Morphology and metabolism of an aortic intima-media preparation in which an intact endothelium is preserved.