Fat transport and lymph and plasma lipoprotein biosynthesis by isolated intestine.

An apparatus and procedure are described for investigating fat transport and lipoprotein biosynthesis in isolated, lymph-cannulated rat intestine perfused with blood under physiological conditions. The small bowel, cecum, proximal half of the colon, and attached mesentery were removed into a tissue bath and perfused vascularly in a recycling system free of blood-air interfaces. Perfusion was continued for 5 hr. Lymph flow, glucose utilization, and oxygen consumption continued unchanged, as did intestinal motility and glucose and water transport from the lumen. No measurable lactate was produced. When 70 micro moles of soybean oil and 9 micro moles of lecithin were infused luminally, more than 50% of the fatty acids were recovered in the lymph, 90% as triglycerides of which 75% appeared in chylomicrons with average diameters estimated to be 100-200 nm, based on their phospholipid content. The preparation incorporated [(3)H]-lysine into the protein moieties of lipoproteins of d < 1.006 g/ml (chylomicrons plus very low density) which appeared in lymph and accounted for more than 30% of all labeled lymph protein. No labeled d < 1.006 lipoproteins appeared in the perfusate. [(3)H]Lysine was also incorporated into the d 1.006-1.21 lipoproteins of both lymph and perfusate, but the specific activity of the former was 500 times as high as the latter, indicating that d 1.006-1.21 as well as d < 1.006 lipoproteins are produced by gut and reach the blood via mesenteric lymph. Most of the labeled d 1.006-1.21 protein appeared to be high density lipoprotein (d 1.063-1.21).