Intestinal biosynthesis of apolipoproteins during active fat absorption in rabbits.

: To gain some insight in the biosynthesis of apolipoproteins in small intestinal walls of rabbits we investigated the in vivo incorporation of [14C]leucine into mesenteric lymph lipoproteins during active fat absorption. The labeled amino acid was predominantly incorporated into the apo B-containing lipoproteins, but also in HDL. More than 40% of total lymph radioactivity were associated with the lipoprotein bound apolipoproteins of chylomicrons, VLDL and HDL. About half of this radioactivity was incorporated into apo B, predominantly into that of the triglyceride-rich lipoproteins. Apo A-I and apo A-IV contained about 17 and 3% of total lymph radioactivity, respectively. In contrast, no radioactivity was detectable in the gel zones corresponding to plasma apo E or lower molecular weight peptides (apo C-II and C-III). During active fat absorption the small intestine of rabbits secretes apo B and apo A into mesenteric lymph, which are obviously necessary for the lymphatic transport of lipids.