TRANSFER OF LIPOPROTEIN(A) AND LDL INTO AORTIC INTIMA IN NORMAL AND IN CHOLESTEROL-FED RABBITS

To study the relative atherogenic potential of lipoprotein(a) [Lp(a)], the transfer of Lp(a) and LDL into the arterial wall was compared in normal rabbits, cholesterol-fed rabbits, and normal rabbits in which t he plasma concentration of Lp(a) before injection of labeled lipoprote ins was increased by an intravenous mass injection of 45 mp Lp(a). Aor ta was removed either 60 minutes or 180 minutes after intravenous inje ction of a mixed preparation of human I-125-Lp(a) and I-131-LDL; intim al clearance was calculated as radioactivity in aortic intima/inner me dia divided by the average concentration of the appropriate radioactiv ity in plasma and by the length of the exposure time. The intimal clea rance of labeled Lp(a) and LDL in the aortic arch after 60 minutes of exposure was 87+/-9 and 47+/-7 nL . cm(-2). h(-1) (n=9) in normal rabb its and 82+/-14 and 62+/-10 nL . cm(-2). h(-1) (n=10) in cholesterol-f ed rabbits; after 180 minutes of exposure, the intimal clearance of la beled Lp(a) and LDL was 62+/-14 and 84+/-21 nL . cm(-2). h(-1) (n=6) a nd 30+/-6 and 47+/-12 nL . cm(-2). h(-1) (n=4) in cholesterol-fed and Lp(a)-injected rabbits, respectively. Linear regression analysis showe d positive associations between intimal clearance of the two lipoprote ins in all four groups of rabbits in the aortic arch, the thoracic aor ta, and the abdominal aorta. Aortic immunoreactivity of human apolipop rotein(a) was detected in the intima in association with fatty streak lesions, predominantly within the cytoplasm of foam cells. These resul ts suggest that Lp(a) is transferred into the aortic intima by a mecha nism similar to that for LDL and that Lp(a) can be taken up by intimal foam cells; however, Lp(a) and LDL may be metabolized differently upo n entrance into the arterial wall.