Transmucosal triglyceride transport rates in proximal and distal rat intestine in vivo

A.L Wu,S.B Clark,P.R Holt

doi:10.1016/s0022-2275(20)36711-0

Abstract

Transmucosal transport rates for triolein in proximal and distal intestine were compared in unanesthetized rats. Emulsified [1-14-C] triolein together with bile and pancreatic juice from donor rats was infused for 6 hr into either the duodenum or the midpoint of the small intestine at such a rate that absorption was essentially complete in both regions of the intestine. Lymph was collected from the thoracic duct during triolein infusion and for an additional 6-hr period. The decrease in the rate of lymphatic output of labeled fat was found to follow a simple exponential function in all animals. This rate of decrease (decay rate) was used to calculate the half-times of lipid turnover through the intestinal wall and the fractional output rates. Distal intestine transported lipid 40% more slowly than proximal intestine, and the difference was associated with a greater accumulation of triglyceride in the distal intestinal wall. Chylomicron synthesis and/or release is the rate-limiting step for distal lymphatic fat transport in vivo, whereas fat uptake from the lumen is rate limiting for proximal intestine.

Highlights

Transmucosal transport rates for triolein in proximal and distal intestine were compared in unanesthetized rats
Es. 1 where y is the amount of lipid 14C in the tissue at any given time, b is the fraction of the tissue lipid 14Ccontent leaving the tissue in unit time, A is the amount of lipid I4C
The results demonstrated that the fractional turnover rate of [''C]triolein through the intestinal wall in vivo was about 40% slower in distal compared with proximal halves of rat intestine, under experimental conditionsin which the luminal uptake rates were complete in the two regions

Summary

Introduction

Transmucosal transport rates for triolein in proximal and distal intestine were compared in unanesthetized rats. The decrease in the rate of lymphatic output of labeled fat was found to follow a simple exponential function in all animals This rate of decrease (decay rate) was used to calculate the half-times of lipid turnover through the intestinal wall and the fractional output rates. T h e regional tissue lipid concentrations best fitted a mathematical model that suggested that maximal lipid uptake rates from the lumen were equal in most regions of intestine but that distal intestine was relatively deficient in triglyceride output on the serosal side. T h e present study was designed to test this model by direct measurement of fractional triglyceride output rates in proximal and distal intestine using direct regional perfusion under conditions where uptake from the lumen was complete.

Methods

Results

Conclusion