The lymphatic absorption of fatty acids and output of phospholipids are lowered by estrogen replacement in ovariectomized rats

Abstract

The lymphatic absorption of fatty acids and output of lipids during intraduadenal lipid infusion were compared in Sprague-Dawley ovariectomized rats with (OXE) and without (OXP) estradiol implants. A time-release estradiol pellet (25 μg/day/rat) was implanted subcutaneously in the OXE rats and a placebo pellet in OXP rats. At 4 weeks, the rats were fitted with lymph cannula and infused at 3.0 ml/hr via a duodenal catheter with a lipid emulsion containing 3.2 μCi 14C-linoleic acid ( 14C-LA), 171 μmol LA, 488 μmol triolein, 520 μmol sodium taurocholate, and 1.5 μmol α-tocopherol in 24 ml phosphate buffered saline (pH 6.4). Lymph was collected at hourly intervals for 8 hours via a mesenteric lymph cannula. The average rate of lymph flow was reduced in OXE (1.4 ml/hr), compared with that of OXP rats (2.2 ml/hr). The total cumulative absorption of 14C-LA during the 8-hr period, as expressed in % dose, was significantly lower in OXE (26.9 ± 5.2%) than in OXP rats (33.6 ± 4.0%). The lymphatic outputs of fatty acids (16:0, 18:0, 18:1, 18:2, and 18:3) also were significantly reduced in OXE rats. The amount of 14C-LA absorbed into the lymph were highly correlated (r = 0.85, P < 0.05) with the amount of phospholipid (PL) released. The results provide the first evidence that the rate of lymphatic absorption of lipids is reduced by estrogen replacement in ovariectomized rats. This may be caused by a limited availability of PL to the enterocyte during chylomicron formation.