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Male Sprague­Dawley strain rats were fed with a diet containing 0.4 per cent β-aminopropionitrile, beginning at 21 days of age. Elastin, collagen and total hexosamine content of the aortas were determined after 7, 14 and 21 days of this diet. Morphologic examination was paralleled with the chemical investigation. Elastin content of the aorta gradually decreased, reaching a minimum after 14 days of feeding. It then recovered, closely approaching the control value. The appearance of abnormal elastic material in interlamellar space, and the disappearance of interlamellar elastic fibers were observed. No significant differences in total collagen content were observed between experimental and corresponding control rats. The argyrophilic fibrous sheath of the medial elastic lamellas disappeared in the lathyritic rat aorta. A considerable increase in total hexosamine content was found in the lathyritic rat aorta at 21 days of the diet. Histologically, a localized accumulation of acid mucopolysaccharide was demonstrated along the inner elastic lamellas of the media, even in the 7-day specimen. Remarkable accumulation was seen in the rat aorta at 14 and 21 days of the lathyrogenic diet. The possible significance of these findings is discussed. [ABSTRACT FROM AUTHOR]

1. The authors made quantitative determinations of the elastin content of the aorta and the pulmonary artery in autopsy tissue specimens from Japanese varying in age from newborn infants to an 81-year old, in cases of accidental deaths (35 males and 22 females), using Scarselli's method. 2. Preliminary electron microscopic observations revealed that elastic fibers of rabbit aorta were fairly selectively diminished by the 4 per cent pancreatin solution, pH 9.5, which was used in Scarselli's method. 3. Elastin content of the aorta in each decade is as follows: 0 to 10 years, 32.9 per cent per nig of sample, dry weight; 11 to 20 years, 36.0 per cent; 21 to 30 years, 29.3 per cent; 31 to 40 years, 24.8 per cent; 41 to 50 years, 25,1 per cent; 51 to 60 years, 21.6 per cent; 61 to 70 years, 22.0 per cent; and 71 to 81 years, 21.1 per cent. 4. Elastin content of the pulmonary artery in each decade is as follows: 0 to 10 years, 27.7 per rent; 11 to 20 years, 31.2 per cent; 21 to 30 years, 26.8 per cent; 31 to 40 years, 27.4 per cent; 41 to 50 years, 27.6 per cent; 51 to 60 years, 25.4 per cent; 61 to 70 years, 23.6 per cent; and 71 to 80 years, 27.5 per cent. Elastin content of the pulmonary artery shows the maximal value in the 2nd decade, as does the aorta, but the decrease of the content is far less marked than that of the aorta. 5. The possible significance of these results was discussed. [ABSTRACT FROM AUTHOR]