Egg Sphingomyelin Lowers the Lymphatic Absorption of Cholesterol and α-Tocopherol in Rats

Abstract

Evidence indicates that phosphatidylcholine (PC) inhibits the intestinal absorption of cholesterol (CH) in rats. This study was designed to determine whether sphingomyelin (SM), structurally similar to PC, also inhibits the lymphatic absorption of CH. Sprague-Dawley rats with lymph cannulae were infused at 3.0 mL/h for 8 h via a duodenal catheter with a lipid emulsion [33.3 kBq 14C-CH, 20.7 μmol CH, 451.7 μmol triolein, 3.1 μmol α-tocopherol (αTP), 75.4 nmol retinol and 396.0 μmol sodium taurocholate in 24 mL of PBS (pH, 6.5)], without egg SM (SM0) as control, or with 5.0 μmol/h (SM5) or 10.0 μmol/h (SM10). Egg SM lowered the lymphatic absorption of 14C-CH in a dose dependent manner. Likewise, SM lowered the lymphatic absorptions of αTP and fatty acid (oleic acid), whereas it had no effect on retinol absorption. SM at a high dose (SM10) lowered the lymphatic outputs of both PC and SM, whereas there was no such effect at a lower dose (SM5). These results indicate that luminal egg SM has an inhibitory effect on the intestinal absorption of CH and other lipids of relatively high hydrophobicity. Our findings suggest that SM, if ingested in sufficient amounts, may inhibit the intestinal absorption of dietary lipids including cholesterol and αTP.