The lymphatic absorption of lipids is normalized by enteral phosphatidylcholine infusion in ovariectomized rats with estrogen replacement

Abstract

Estrogen (ES) replacement previously was shown to decrease the lymphatic absorption of fat with a simultaneous decrease in phospholipid (PL) output in ovariectomized (OX) rats. The present study was conducted to investigate whether intraduodenal infusion of phosphatidylcholine (PC) would normalize the absorption of 14C-linoleic acid ( 14C-LA) and unlabeled oleic acid (OA) in OX rats implanted s.c. with an estradiol pellet (OXE; 25 μg/day/rat), compared with OX rats implanted with a placebo pellet (OXP). Additionally, this study examined whether ES would alter the rate of fatty acid esterification into various lipids in the intestinal mucosa. Both groups were meal-trained and pair-fed for 7 weeks. Each rat with a lymph cannula was infused at 3 mL/hr via a duodenal catheter with a lipid emulsion containing 14C-LA and triolein (380 μmol) with or without PC (41 μmol). Lymph was collected hourly for 8 hr via a lymph fistula. Without PC infusion, the total lymphatic absorption of 14C-LA was significantly lower (26.0 ± 3.4% dose) in OXE rats than in OXP rats (31.8 ± 2.0% dose) with a close parallel decrease in OA output at 2 hr and thereafter. Also, the total lymphatic secretion of PL was significantly lower in OXE rats (26.5 ± 2.4 μmol) compared with OXP rats (37.1 ± 4.1 μmol). When PC was infused, the total lymphatic absorption of 14C-LA and OA in OXE rats was restored completely to normal, whereas PC infusion had no effect on the lymphatic outputs of 14C-LA or OA in OXP rats. The lymphatic outputs of PL were enhanced markedly in both groups with PC infusion. The hourly output of PL was correlated highly with the absorption of 14C-LA ( r = 0.81) and OA ( r = 0.78). Regardless of whether lysophosphatidylcholine (lysoPC) was present in the intestinal lumen, the rates of mucosal 14C-LA incorporation into triglycerides (TG), PL, and other lipids were not affected by ES treatment. The results indicate that the slower rate of lymphatic absorption of fatty acids in ES-treated rats is not due to alteration in mucosal fatty-acid esterification, but to a limited availability of PL to the enterocyte. This may be associated with an inhibitory effect of ES on the hepatic secretion of PL via the biliary route.