Enteral infusion of phosphatidylcholine increases the lymphatic absorption of fat, but lowers α-tocopherol absorption in rats fed a low zinc diet☆

Abstract

Our previous study has shown that the lymphatic absorption of both fat and α-tocopherol (αTP) is lowered markedly in rats fed a low zinc diet, with a parallel decrease in lymphatic phospholipid (PL) output. This study was conducted to determine if enteral infusion of phosphatidylcholine (PC) could restore lymphatic absorption of fat and αTP in zinc-deficient rats. One group of rats was fed an AIN-93G diet containing 3 mg Zn/kg (low zinc; LZ) and the other was fed the same diet but containing 30 mg Zn/kg (adequate zinc; AZ). Rats were trained to consume two meals daily of equal amounts of food. At 6 wk, each rat with lymph fistula was infused at 3 mL/h with a lipid emulsion containing 3.6 μmol αTP and 565 μmol [carboxyl- 14C]-triolein ( 14C-OA), with or without 40 μmol 1,2-dilinoleoyl-PC in 24 mL PBS at pH 6.4. The lymphatic absorptions of fat and αTP were determined by measuring 14C-radioactivity and αTP appearing in the mesenteric lymph collected hourly for 8 h. When the emulsion devoid of PC was infused, the absorptions of both 14C-OA (41 ± 4% dose) and αTP (431 ± 55 nmol) in LZ rats were significantly lower than in AZ rats (48 ± 2% 14C-OA dose and 581 ± 70 nmol αTP). When the emulsion containing PC was infused, the absorption of 14C-OA was restored rapidly to normal in LZ rats, along with a parallel increase in lymphatic PL output. However, PC infusion further lowered the absorption of αTP to 311 ± 20 nmol/8 h in LZ rats and also lowered the absorption of αTP in AZ rats (347 ± 48 nmol/8 h). The results demonstrate that low zinc intake results in impaired intestinal absorption of both αTP and fat. The findings also indicate that PC significantly improves the intestinal absorption of fat, but inhibits αTP absorption, suggesting that PC affects the intestinal absorption of αTP and fat via distinctly different mechanisms.