The synthesis of soluble elastin, newly synthesized insoluble elastin and total accumulated insoluble elastin was measured in aortic tissue of chickens ranging in age from the 11-day embryo to the adult chicken. Synthesis of soluble elastin reached a maximum in the 1st week after hatching, then decreased rapidly with a second transient increase between 4 and 6 weeks and thereafter decreased continuously until synthesis could no longer be detected in the 35-week-old adult. A portion of this newly synthesized soluble elastin was insolubilized even during 1 h of incubation by a β-aminopropionitrile-inhibited mechanism. Total insoluble elastin accumulated rapidly in aortic tissue in the late embryonic stages and reached a plateau about 1 week after hatching, after which time the proportion of the protein in the tissue remained constant. Synthesis of soluble elastin and total insoluble elastin was also determined in aortic tissue of chickens raised on a diet containing 2% cholesterol for 14 weeks after hatching. This cholesterol-rich diet had an early, but transient effect on the synthesis of soluble elastin, shifting the age of maximal synthesis to 1 to 2 weeks after hatching. However, by 6 to 8 weeks on the diet there was no difference in soluble elastin synthesis between normal and cholesterol-fed groups. Although prolonged cholesterol feeding resulted in serum cholesterol levels 10 times normal, aortic tissue cholesterol levels 3 times normal and grossly visible atherosclerotic lesions, no reinitiation of soluble elastin synthesis or alteration in the quantity and character of insoluble aortic elastin could be detected.

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