Rate-limiting steps in steady-state intestinal absorption of trioctanoin-l-14C

Abstract

A B S T R A C T During continuous intraduodenal infusion of emulsified fat in rats, a steady state of intestinal absorption is achieved.Maximal steady-state absorption of trioctanoin, a medium-chain triglyceride (MCT), by unanesthetized, restrained rats was found to be the same after total bile diversion as in controls (1560 ,/moles of fatty acid per hr).After pancreatic and bile diversion, absorption of MCT was still one-third as rapid as in controls, and mucosal uptake apparently occurred in the form of unhydrolyzed triglyceride. Returning bile to the intestinal lumen during pancreatic diversion did not increase the absorption rate.From intestinal tissue lipid-14C concentrations measured during steady-state maximal absorption it was possible to calculate turnover times for labeled lipid passing through the mucosal cells. Mucosal turnover times of about 4 min for control and bile-diverted rats, and about 20 min for animals with pancreatic diversion were obtained.The rate-limiting step in octanoic acid absorption in control and bile-diverted rats was probably mucosal penetration. During absorption of unhydrolyzed triglyceride by pancreatic flow-diverted rats, both passage from the lumen into the mucosal cell and intracellular lipolysis were rate-controlling factors.This work was published in part as an abstract (1).

Inhibition of steady-state intestinal absorption of long-chain triglyceride by medium-chain triglyceride in the unanesthetized rat

“…Computations were based on the data of Mattson and Volpenhein (13) which implied that 75% of triolein fed to rats was absorbed as fatty acid. It was assumed that trioctanoin already absorbed had entered the mucosa as free fatty acid (6). The results of such calculations in animals receiving maximal infusions of triolein with differing amounts of trioctanoin appear in When the total fatty acid (LC and MC) released into the intestinal lumen in 2 hr in all experimental groups was plotted against the total lipid infused (Fig.…”

“…TRIOCTANOIN-'4C INFUSION RATE (pEq FA/hr) FIGURE 6 Effect of triolein-9,10-8H infusion on steady-state absorption of trioctanoin-1-14C. 0, mean trioctanoin absorption rates.…”

“…Both are hydrolyzed to fatty acids and glycerides by pancreatic lipase in the intestinal lumen (4,5), and the products of lipolysis of both triglycerides probably enter the mucosal cell membrane from an aqueous luminal phase. The absorption of medium-chain fat differs from that of long-chain fat in the lumen, where mediumchain fatty acids do not require bile salts for adequate solubilization (6), and inside the mucosal cell, where they are not reesterified (7) but pass rapidly into the portal blood stream. One approach to the understanding of the rate-controlling steps in fat absorption was to study the steady-state absorption of a typical long-chain triglyceride, triolein (LCT), in the presence of graded amounts of a typical medium-chain triglyceride, trioctanoin (MCT).…”

Hydrolysis and Absorption of Medium-Chain Triglycerides and Soy Oil

“…However, the use of olive oil as a vehicle for administering the trioctanoin in these studies may have interfered with its utilization. Clark and Holt (10) have shown that diversion of pancreatic juice decreases absorption of trioctanoin to one-third of the normal rate in the rat, but that bile diversion has no effect on MCT absorption.…”

Pancreatic Extracts Are Necessary for the Absorption of Elemental and Polymeric Enteral Diets in Severe Pancreatic Insufficiency

“…This assumption has been recently challenged by the observation that a similar nitrogen balance can be achieved in pancreatectomized patients using whole protein or protein hydrolysates as nitrogen source (7); moreover. pancreatic enzymes enhance the digestion of medium-chain tri-glycerides in rats (8) and their absorption in infants with cystic fibrosis (9). The aim of this study was to test the absorption of elemental and polymeric diets in pancreatic insufficiency and to evaluate the possible effect on it of highdose pancreatic supplements.…”