These studies are directed toward identifying an endogenous androgen imprint on metabolic and mechanical properties of elastin and collagen during the post-natal and pre-adult period in rats. The basic question is whether the post-natal rise in plasma androgens, by influencing the arterial elastin and collagen polymerization and turnover, conditions the arterial wall for focal structural changes which lead to the ultimate lesion of obstructive atheromatosis. Currently, we know that the neonate male has higher concentrations of elastin and collagen in the aorta than the female and that the profiles of borohydride-reducible elastin and collagen cross-links are different in the two sexes. Over the past year, the elastin cross-links were labeled with radioactive lysine. Comparisons of the formation, turnover and accumulation of aortic elastin and collagen in the two sexes from the weanling to adult periods are being made. After identifying and characterizing an androgen imprint on aortic elastin and collagen, we will test for sex differences in the biomechanical properties of these two structural proteins. Then the mechanism and the regulation of the androgen imprint will be investigated.