The distribution of radio-iodinated serum albumin and low-density lipoprotein in tissues and the arterial wall

Abstract

Plasma low-density lipoprotein labelled in the peptide component with radioiodine (RI-LDL) was injected into 11 patients in coma, in whom death was considered inevitable. Injected material was primarily Sf 0–9 LDL. The serum turnover of RI-LDL was followed until death of the patient. Parallel studies were carried out in another 11 subjects using radioiodinated human serum albumin (RI-HSA). Various tissues were recovered at necropsy and their radioactivity measured. The temporal pattern of radioactivity distribution in tissues was studied by comparing results from the individual patients in ascending order of the time elapsing between administration of labelled proteins and recovery of tissue. Results for RI-LDL and RI-HSA tissue to plasma radioactivity ratios were qualitatively similar.Equilibration between plasma and tissue radioactivity was most rapid in liver and spleen. Intima and inner media of aorta and coronary arteries showed rising ratios of tissue to plasma radioactivity over the 14–16-day maximum duration of these studies, and higher levels of radioactivity were reached in the arch and abdominal segments than in the thoracic aorta. Outer medial tissue/plasma ratios were lower and appeared to reach equilibrium earlier. The results show that plasma LDL peptide does enter the inner arterial wall, presumably across the intima, and that the intima may be the site of a slowly exchanging LDL pool.