Histology of normal aortas in non-human primates with emphasis on diffuse intimal thickening (DIT).

Little information is available on the histology of the normal aorta in non-human primates, despite their extensive use in atherosclerosis research. This paper consists of a detailed histologic description of normal aortas from 28 non-human primates, including 20 species. Medial and adventitial coats were essentially normal in all animals, and the former were composed of lamellar units similar in structure to those described in detail by other investigators. Intimal thickenings were present in 24 of the 28 individuals. These thickenings were similar in morphology to those of diffuse intimal thickening (DIT) in humans and other animals, and were more prevalent in older animals and in larger animals. The thickenings were not more prevalent or more pronounced in any particular region of the aorta, and their distribution did not provide a clue as to their etiology. Findings suggested that the thickenings underwent recognizable states of growth and maturation, and that growth was accomplished by the addition of smooth muscle cells at the intimomedial junction.