Intraduodenal Infusion of Lysophosphatidylcholine Restores the Intestinal Absorption of Vitamins a and E in Rats Fed a Low-Zinc Diet

Abstract

Our previous work has shown that the lymphatic absorptions of lipids and lipid-soluble vitamins, retinol and α-tocopherol (αTP), are lowered markedly in rats fed a low-zinc (LZ) diet in parallel with lower lymphatic phospholipid outputs. Phosphatidylcholine (PC), when infused enterally, restored the absorptions of fat and retinol, but further lowered the absorption of αTP in rats fed the LZ diet. This study was conducted to determine whether a luminal infusion of lysophosphatidylcholine, a product of PC hydrolysis by pancreatic phospholipase A2 (PLA2), would simultaneously restore the absorptions of retinol and αTP in LZ rats. Rats were trained to consume two meals per day and were divided into two groups. One group was fed an AIN-93G diet containing a LZ (3.0 mg Zn/kg), and the other was fed the same diet, but containing adequate zinc (AZ; 30.0 mg Zn/kg) for 6 weeks. Rats with lymph cannula were infused at 3.0 ml/hr for 8 hr with a lipid emulsion containing retinol, αTP, and 14C-labeled triolein (14C-oleic acid) with or without 1-oleoyl-2-hydroxy phosphatidyicholine (lysoPC) in 24 ml of PBS (pH 6.5). When the lipid emulsion without lysoPC was infused, the absorptions of retinol and αTP were significantly lower in LZ rats (retinol, 13.2 ± 1.5 nmol; αTP, 430.6 ± 66.8 nmol) than in AZ rats (retinol, 18.2 ± 1.0 nmol; αTP, 543.8 ± 58.9 nmol). The lower absorptions of the vitamins in LZ rats occurred in parallel with a significant decrease in 14C-oleic acid absorption. When the emulsion containing lysoPC was infused, however, absorptions of the vitamins (retinol, 18.4 ± 3.0 nmol; αTP, 777.2 ± 92.1 nmol) in LZ rats were restored completely to the control levels (retinol, 20.4 ± 2.8 nmol; αTP, 756.3 ± 136.1 nmol). The results suggest that the luminal hydrolysis of PC to lysoPC by PLA2 may be impaired in LZ rats, resulting in impaired absorption of fat and the fat-soluble vitamins.