In view of the role of the small intestine in lipoprotein synthesis and bile salt reabsorption, we have determined plasma lipid fractions and apolipoproteins A-I, A-II, and B at regular intervals in 26 patients who underwent jejunoileal bypass surgery for morbid obesity. After surgery, no change in plasma triglycerides was noted, but there was a prompt and significant fall in total plasma cholesterol and low density lipoprotein cholesterol, which persisted beyond 2 yr. Plasma apolipoprotein B levels did not fall concurrently, and hence the protein/lipid composition of low density lipoprotein was permanently altered by the surgery. Levels of high density Jipoprotein cholesterol were low before bypass surgery, decreased after surgery, and rose thereafter toward the normal range. Similar changes in apolipoprotein A-I and A-II values were noted. These postoperative alterations in plasma lipid and apoprotein levels demonstrate the importance of intestinal absorptive integrity in the regulation of lipoprotein metabolism.
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