Metabolism of iodinated high density lipoprotein subunits in the rat III. Comparison of the removal rate of different subunits from the circulation

Abstract

A comparison of the t 1 2 of in vivo and in vitro labeled rat high density lipoprotein showed that they behave metabolically alike. It was shown that labeling of high density lipoprotein with 125I in vitro, and with [ 14C leucine in vivo, results in a similar distribution of label among the subunits of the apolipoprotein. The rates of degradation of the various subunits of high density lipoprotein of rats were studied. After injection of radioiodinated high density lipoprotein, the distribution of radioactivity in the subunits of high density lipoprotein was determined; it was found to be unchanged between 1 and 48 h after injection. This indicates that the various subunits of high density lipoprotein have similar rates of removal. When the t 1 2 of these subunits was measured, a rather similar half life of 8.5–11.5 h was found. A fast and a slow component were shown to be present in the turnover curve of in vivo labeled very low density lipoprotein. The fast component had a t 1 2 less than 1 h while the slow component had a t 1 2 of 10–12 h. After injection of radioiodinated high density lipoprotein, radioactivity appeared in some of the subunits of very low density lipoprotein. Assuming a common pool for these subunits of very low and high density lipoproteins, these data would suggest that these very low density lipoprotein subunits have a slower rate of removal than the other subunits of very low density lipoprotein.