Changes of serum apolipoprotein levels after oral administration of fat in human subjects

Abstract

Changes of serum apolipoprotein levels were studied every hour for 6 h after the administration of 55 g butter to 8 healthy male subjects. The mean serum apo A-IV level was significantly increased at 4 h ( P < 0.05) after fat ingestion compared to the mean initial level, although no significant changes of levels in other apolipoproteins (apo A-I, A-II, B, C-II, C-III, and E) were observed. The mean apo A-IV level in the triglyceride-rich lipoprotein (TRL) fraction ( d < 1.006) increased progressively over 6 h. In all 8 subjects, the time of peak concentration of apo A–IV in TRL fraction was delayed by 1–2 h compared to that in whole serum. On the other hand, the mean apo B-48 level in the fraction reached a peak at 4 h. These results raise the possibilities that some apo A–IV, newly synthesized or already existing in intestinal cells, may be directly secreted into the venous circulation and that apo A-IV and apo B-48 may distribute differently in different sizes of chylomicron. Alternatively, the amount of each apolipoprotein synthesized may depend upon the content of ingested fat. It is suggested that apo A–IV production by intestinal cells does not appear to be regulated by the rate of fat transport, and that apo A–IV does not play an important role in chylomicron formation compared to apo B-48.