Concurrent Measurement, in Unanæsthetized Rats, of Intestinal Transport and Fat Absorption From the Lumen

Abstract

A test meal containing emulsified coconut oil mixed with water soluble polyethyleneglycol (PEG) of high mol. wt. was given to rats by gastric intubation. At intervals up to 5 hr. after the meal, rats were killed and the amounts of PEG and fat recoverable from the stomach, small intestine and coecum were measured. PEG was not absorbed from, nor broken down in, the intestine and left the stomach at the same rate as the emulsified fat. It was, therefore, a suitable reference substance. With a test meal of constant volume, 4 ml., increasing doses of fat, 0-25, 0.5 and 140 ml., decreased the rate of stomach emptying and of propulsion of PEG through the small intestine. The rate of fat absorption was limited by the decreasing rate of stomach emptying but there was no indication that the absorptive capacity of the small intestine had been saturated. The ratio of recovery of fat: PEG in successive segments of the small intestine indicated that fat was absorbed chiefly in the distal half. This was probably due to rapid propulsion of material through the proximal half rather than to any lack in capacity for fat absorption proximally.WHEN a suitable reference substance has been added to a test meal, it is possible to follow the progress of the meal through the intestine and to assess the extent to which foodstuffs are absorbed from a given segment. The reference substance must be biologically inert and unabsorbable. It also must pass along the intestine at the same rate as the material whose absorption is being investigated.Reference substances have been used mostly in experiments on watersoluble foodstuffs [Reynell and Spray, 1956 a]. Their use with fat presents difficulties, because the changes which fat undergoes during digestion and absorption are not easily reproduced with an inert, unabsorbable substance. Borgstrom, Dahlquist, Lundh and Sjovall [1957] have used, in human subjects, polyethyleneglycol (PEG) of mol. wt. 3000-3700. They considered that this was a reliable reference substance, despite its high solubility in water, when the fat in the test meal was finely emulsified. PEG therefore seemed worthy of trial in experiments on fat absorption in rats. The objects of these experiments were: (i) to see how the rate of passage of a gastric test meal or its residues through the small intestine was affected by increasing the dose of fat; (ii) to assess the relative importance of proximal and distal segments in fat absorption, and (iii) to see whether the rate of fat absorption was limited by the absorptive capacity of the small intestine or by the rate at which fat was admitted from the stomach.

Site of Fat Absorption and Localization of 3-Hydroxy-3-methylglutaryl Coenzyme A (HMG-CoA) Reductase Activity along the Small Intestine of Rats

“…3 and 7). These observations are in agreement with those of Aberdeen et al 17 ) They compared the ratio of fat to polyethyleneglycol in successive segments of the small intestine of rats and found that fat was absorbed chiefly in the distal half.…”

The digestion and absorption of sucrose by the intact rat

“…(1960) and verified by us, may be that the rinsing of the space between the villi is inefficient. When longer absorption times are used, the solution reaches the lower parts of the intestine where the villi are not so numerous, and consequently more of the polyethylene glycol is recovered (Aberdeen et al 1960). By homogenization of the intestine this difficulty is overcome.…”

Apolipoprotein A-V deficiency enhances chylomicron production in lymph fistula mice

“…While apoA-V is well-demonstrated to profoundly regulate fasting plasma TG in both mice (20,49,15,49,61,70,64) and humans (1,14,23,32,21), little is known about the contribution of apoA-V to lipid absorption and postprandial TG metabolism. Results from apoA-V transgenic mice (15) and adenovirus-mediated gene transfer experiments to mice (49) suggest that apoA-V suppresses the surge in plasma TG after a lipid meal.…”

“…A lipid emulsion was prepared by dissolving triolein {labeled with [9, H(N)]triolein}, cholesterol {labeled with [1,[2][3][4][5][6][7][8][9][10][11][12][13][14] C(N)]cholesterol}, and egg phosphatidylcholine in chloroform, which was then evaporated under nitrogen gas. The chloroform-free mixture was emulsified with 19 mM sodium taurocholate (NaTC) in phosphate-buffered saline (PBS) at pH 6.4.…”

“…Samples from the hourly lymph, luminal washings, and intestinal tissues were taken for determination of radioactivity by scintillation spectroscopy. Lipids recovered from the intestinal lumen and mucosa at the end of the study allowed for analysis of steady-state accumulation of lipids that were not secreted (1).…”