The uptake of oleic acid by rat small intestine: a comparison of methodologies

Role of small intestine in caloric compensations to oil premeals in rats

We postulated that dose-responsive satiety after oil premeals varies with the number of gut sensors stimulated by lipolytic products along intestine. These experiments in fasted rats on satiety after oil premeals were performed to 1) determine whether satiety was induced by lipolytic products but not triglycerides; 2) confirm that oil empties from the stomach at rates that vary with oil loads; 3) ascertain that increasing rates of oil entry into duodenum extend the length of gut contacted by lipolytic products; and 4) judge whether length of gut contacted correlated with dose-responsive satieties to dietary oils. 5) Using specific antagonists, we attempted to define how satiety was signalled by gut sensors. Timing and degrees of satiety did not correlate with timing and extent of gastric distensions but, rather, with the timing and extent of spread of lipolytic products along small bowel. Satiety after the highest premeal load of oil was blocked by Pluronic L-81, an inhibitor of intestinal secretion of apolipoprotein A-IV, but was unaffected by MK-329 (a specific antagonist of cholecystokinin) or by capsaicin blockade of chemosensory nerves.

Free fatty-acid uptake by isolated rat hepatocytes

In isolated rat hepatocytes, the rate of palmitic acid binding and uptake is directly related to the concentration of free fatty acid (FFA) in the medium. After their entry into the cell, FFA are immediately incorporated into cellular phospholipids and triglycerides and no accumulation of free fatty acids can be demonstrated inside the cell. The rate of free fatty-acid uptake remains unchanged after incubation in a 2 mM KCN containing medium, indicating that in the range of fatty-acid concentrations used in this study, this phenomenon does not require energy.

The absorption and transport of dietary cholesterol in the presence of peanut oil or randomized peanut oil

Peanut oil has been shown to be unexpectedly atherogenic for cholesterol-fed rats, rabbits and rhesus monkeys. However, randomization (rearrangement of fatty acids to random distribution) of peanut oil significantly reduced its atherogenicity for rabbits and monkeys. This study was conducted to investigate whether the absorption and transport of dietary cholesterol was altered in the presence of peanut oil or randomized peanut oil, thereby accounting for the difference in the atherogenicity of the two diets. Intestinal lymph fistula rats were infused intraduodenally with a lipid emulsion at a rate of 3 ml/hr. The lipid emulsion contained either peanut oil (control) or randomized peanut oil (experimental) (10 mM), 14C-cholesterol (1.3 mM) and sodium taurocholate (19 mM) in phosphate-buffered saline, pH 6.4. Lymph triglyceride, cholesterol and phospholipid outputs were similar in both groups of rats during fasting and subsequently during lipid infusion. Comparable recovery of 14C-cholesterol from the intestinal lumen and the intestinal mucosa of the control and the experimental rats showed that the absorption and transport of dietary cholesterol were similar in both groups of rats. Analyses of the fatty acid of both lymph and intestinal mucosal lipid again failed to reveal a difference between the 2 groups of rats. It is concluded that the difference in the atherogenicity between the peanut oil and the randomized peanut oil is probably caused by events subsequent to the release of cholesterol containing chylomicrons and very low density lipoproteins by the small intestinal epithelial cells.

Food intake after intragastric meals of short-, medium, or long-chain triglyceride

Food-deprived Sprague-Dawley rats were given equicaloric intragastric infusions of mixed meals consisting largely of short- (SCT), medium- (MCT), or long-chain triglyceride (LCT). When animals were allowed to feed 20 min after infusion, there was an immediate reduction of food intake that was sustained over the 2 hr feeding period. During the first hour of feeding, the SCT, which is digested and absorbed more rapidly than the MCT or the LCT, was more effective per calorie in reducing food intake than these longer-chain triglycerides. However, during the second hour, cumulative intakes after the different triglyceride infusions were not significantly different. Equicaloric infusions of the MCT and the LCT resulted in equivalent reductions of food intake at all times. The satiety effects of these two triglycerides appear to be related to their caloric properties rather than to chain length. Since the LCT reduced food intake before the absorbed fat could have entered the blood to stimulate satiety signals, this satiety effect may be mediated by a gastroenteric signal. None of the triglyceride infusions resulted in a conditioned taste aversion suggesting that food intake was reduced through normal satiety rather than through discomfort.

Lipid absorption in unanesthetized, unrestrained rats. Effects of 4-aminopyrazolopyrimidine and ethinyl estradiol

Emulsified triacylglycerol containing [14C]palmitate was infused intraduodenally in unanesthetized, unrestrained animals treated with 4-aminopyrazolopyrimidine or pharmacologic doses of ethinyl estradiol. 4-Aminopyrazolo-pyrimidine practically eliminated the appearance of radioactivity in plasma but in ethinyl estradiol-treated animals the peak of radioactivity and shape of the plasma curve were similar to control, although lower in amplitude. A delayed appearance of radioactivity was also observed in 48-h- compared to 15-h-fasted controls, suggesting a requirement for induction of lipoprotein production prior to fat absorption.

The importance of the lysophosphatidylcholine and choline moiety of bile phosphatidylcholine in lymphatic transport of fat

A luminal supply of biliary phosphatidylcholine is important in the translocation of absorbed fat into lymph and in the amount and composition of phosphatidylcholine concurrently synthesized. This study was undertaken to determine whether the effect was due to absorbed lysophosphatidylcholine, to a specific (1-palmitoyl) biliary lysophosphatidylcholine or to extra choline supplied by lysophosphatidylcholine. Rats with bile fistulae and thoracic duct lymph fistulae were given test meals of oleic acid and monoolein (molar ratio 2 : 1) infused duodenally for 8 h. Addition of choline chloride to the test meal increased lymphatic output of triglyceride and phospholipid but not to values found previously in rats with supplements of bile phosphatidylcholine or with bile ducts intact. Addition of dioleoyl phosphatidylcholine increased triglyceride and phospholipid output to values found in rats with intact bile ducts. Since dioleoyl phosphatidylcholine was as efficient as biliary phosphatidylcholine it was concluded that a luminal supply of 1-palmitoyl lysophosphatidylcholine was not essential. It seemed likely from the smaller effect of supplemented choline and from the fatty acid composition of lymph phosphatidylcholine that the essential requirement was a supply of absorbed lysophosphatidylcholine for rapid reacylation to phosphatidylcholine.

Comparison of linoleic acid and stearic acid absorption by the gallbladder

The absorption of [14C]linoleic acid and [14C]stearic acid in guinea pig bile by the in situ guinea pig gallbladder was compared. Linoleic acid was adsorbed at a faster rate than was stearic acid. Differences were also observed in the incorporation of these two fatty acids into complex lipids of the gallbladder mucosa. A greater portion of adsorbed linoleic acid was incorporated into triacylglycerol whereas a greater portion of stearic acid was incorporated into sphingomyelin. The significance of these findings in relation to the fatty acid composition of bile is discussed.

Intestinal lipid absorption: evidence for an intrinsic defect of chylomicron secretion by normal rat distal intestine

Intracellular triglyceride accumulation and delayed chylomicron secretion were demonstrated in distal but not in proximal rat intestine following prolonged steady state fat absorption. After 1 and 4 hr of intraduodenal triolein infusion, the mucosal triglyceride content in distal intestinal segments was greatly increased compared with proximal segments. Electron microscopy at each time interval disclosed greater quantities of lipid droplets within the distal cells and these were much larger than the intracellular droplets in the proximal cells, some attaining an enormous size (9000 mum). When proximal and distal cells were compared at intervals after cessation of a 4 hr triolein infusion, the differences in intracellular lipid accumulation were also evident because, even after 6 hr the distal cells were still filled with large droplets, whereas the proximal cells were almost devoid of fat. These results indicate a basic cellular difference between proximal and distal intestine in the processing of fat and, in contrast to current concepts, suggest that defective chylomicron secretion is not necessarily associated with limited B-apoprotein availability.