Carotenoids in Man. Iii. The Microscopic Pattern of Fluorescence in Atheromas, and Its Relation to Their Growth1

In a previous study of the carotenoid content of human aortic atherosclerosis it was concluded by Blankenhorn, Freiman, and Knowles that these dietary lipids accumulate in direct proportion to the extent and relative age of the lesions in which they occur. A series of graded aortic segments was assayed, and it was found that increased severity of atherosclerosis was accompanied by a parallel increase in the concentration of carote- noids (1). Exact location of these pigments in relation to the microscopic anatomy of atherosclerotic lesions should aid in evaluation of the role of exogenous lipids of this class in the initiation of atheromas and their continued growth. It seemed possible that this might be accomplished by fluorescence microscopy, since carotenoids and vitamin A, on exposure to ultraviolet light, produce a characteristic pale green fluorescence by which they can be exactly localized and roughly quantitated in tissue sections (2). Although Popper (2), and Hamperl (3), who performed surveys of the fluorescence in human tissue, reported no evidence of carotenoids or vitamin A in atheromas, it was decided to reinvestigate this matter in view of the findings of Blankenhorn, Freiman, and Knowles. The surveys of Popper and Hamperl were performed on tissues fixed in formalin, a pro- cedure known to diminish the fluorescence of carotenoids and vitamin A. Therefore, in the study here reported unfixed atheromas were examined. Green fluorescence was found and evidence will be presented to show that this fluorescence is a valid means of localizing carotenoids and/or 'Supported in part by grants-in-aid from the American