Maximal lymphatic triglyceride transport rate from the rat small intestine

In previous studies, we demonstrated that the hydrophobic surfactant Pluronic L-81 blocks lymphatic triglyceride transport from the small intestine and leads to accumulation of triglyceride in the mucosa. The onset of action of Pluronic L-81 is rapid and quickly reversed once its administration is discontinued. We have taken advantage of these effects of Pluronic L-81 on intestinal lipid transport in order to determine the apparent maximal triglyceride transport capacity of the proximal half of the rat small bowel using lymph fistula rats infused intraduodenally with a phosphate-buffered, taurocholate-stabilized emulsion containing 40 mumol [3H]triolein and 0.5 mg Pluronic L-81 at 3 ml/h for 8 h to load the proximal small bowel with lipid. Studies were done in one group of rats in order to be certain that only the proximal half of the small bowel contained 3H-lipid after this period of infusion. In other rats treated similarly, the 8 h of lipid-Pluronic L-81 infusion were followed by infusion of 3 ml/h of 0.15 M salt solution for 5 h. Lymphatic transport of lipid was determined throughout the entire period of infusion. During lipid-Pluronic L-81 infusion, transport of 3H-triglyceride fatty acid into lymph was only 22-27 mumol/h but rose steadily after substitution of saline and reached a maximal transport rate of 109 +/- 6.2 mumol/h (means +/- SE) after 3.5 h. During this 3.5-h period, the amount of 3H-lipid in the proximal mucosa declined from 530 to 263 mumol. While Pluronic L-81 was infused, only very low-density-lipoprotein-sized particles were seen in lymph by electron microscopy, whereas, at the peak of triglyceride transport during saline infusion, chylomicrons of up to 6,000 A were observed in lymph.