Segments Of Rat Small Intestine Research Articles

Intestinal Absorption of Vitamin B12in Patients with Chronic Pancreatic Insufficiency and the Effect of Human duodenal Juice on the Intestinal Uptake of Vitamin B12

The mean absorption of vitamin B12 (Schilling test) was 13.1 +/- 1.0 (% +/- S.E.M.) in 21 patients with chronic pancreatic insufficiency and 17.6 +/- 1.4 in 13 control patients (p less than 0.01). There was no correlation between pancreatic bicarbonate production after secretion stimulation and vitamin B12 absorption in the patient group (r = 0.117). Human duodenal juice reduced the uptake of 57CoB12-rat intrinsic factor (IF) by perfused rat small intestinal segments in vivo (p less than 0.01) as well as the uptake of 57CoB12-human IF by purified guinea-pig intestinal brush borders in vitro (p less than 0.01). The results confirm reduced absorption of vitamin B12 in chronic pancreatic insufficiency, but the mechanism remains uncertain.

The transamination of glutamate and aspartate during absorption in vitro by small intestine of chicken, guinea-pig and rat.

1. Procedures are described for direct measurement of the extent and rate of transamination of glutamate and aspartate over periods of up to 90 min, during absorption in vitro by the small intestine of chicken, guinea-pig, and rat.2. During absorption of dicarboxylic amino acids by rat small intestinal segments circulated through the lumen in vitro, alanine contributed up to 85% of the amino acids appearing in the fluid secreted at the serosal surface. In guinea-pig and chicken intestine, the proportion of alanine in the secreted amino acids did not exceed 60%.3. For the different species studied, a relationship was found between the extent to which the dicarboxylic amino acids were transaminated to alanine and the total amount of GPT found in other studies to be present in the intestinal mucosa. In both rat and guinea-pig small intestine, the proportion of alanine in the total amino acids appearing at the serosal surface was similar in the jejunum and ileum. The rate of appearance of alanine in serosal fluid was greater in the ileum than in the jejunum of the rat.4. Reasons are given for supposing that for all the species studied there is a limit to the capacity of the small intestinal mucosa to subject free dicarboxylic amino acids to transamination. It is concluded, however, that it is unlikely that this capacity will be exceeded under in vivo conditions.

Uptake of micellar lipids by small intestinal segments (under different experimental conditions).

AbstractUptake of radioactive cholesterol, sitosterol and monoolein from micellar solutions was studied under different conditions in rat small intestinal segments both with and without blood supply, and in inverted segments in vitro. The Na+/K+ ratio of the micellar test solution did not influence the uptake of any species of lipid tested. In vivo the uptake of sterols was maximal at 37°C. It had a Q10 of about 3. Three states of sterol uptake were observed. (1) A high uptake of both cholesterol and sitosterol, (2) a low uptake of both sterols, and (3) a low uptake of sitosterol with a high uptake of cholesterol. The latter state corresponds to normal uptake in vivo. These states were demonstrated under different experimental conditions involving exclusion of blood supply to the small intestine, extensive hypothermic treatment of the rat, extensive hypothermic treatment followed by rewarming to 37°C, and biliary drainage followed by uptake experiments with high concentrations of NaTDC or NaTC. It was demonstrated that the normal uptake of sterols could be both irreversibly and reversibly changed into the other abnormal states of uptake.

Transport characteristics of the amino acid analogues, cycloserine and α-methyldopa, using rat small intestine [formula omitted

Everted sacs and everted segments of rat small intestine were used to investigate the transport characteristics of certain amino acid analogues. There was no evidence for the active transport of D- or L-cycloserine, L-dopa nor of the D- and L-isomers of α-methyldopa, using these intestinal preparations. It is assumed that these compounds pass across the intestinal mucosa by simple diffusion.

Effect of S-(1,2- trans-dichlorovinyl)- l-cysteine on the transport of amino acids and glucose by everted segments of rat small intestine

1. 1. Using everted sacs of rat small intestine, S-(1,2-trans- dichlorovinyl)- l-cysteine (DCVC) was found to suppress the active transport of glucose, glycine and a number of l-amino acids including phenylalanine, leucine, valine, alanine and histidine. 2. 2. The inhibition appeared to be proportional to the concentration of DCVC, and was not readily reversed by simple washing technics. 3. 3. There was no marked alteration in the permeability of the intestinal sacs in the presence of DCVC, as measured by passage of d-phenylalanine in either direction. 4. 4. DCVC inhibition of l-phenylalanine uptake by intestinal tissue appears to be a competitive process. 5. 5. DCVC itself undergoes active transport at low concentrations, with greatest transport occurring in the mid-jejunum region of rat small intestine, and least in the duodenum. 6. 6. DCVC transport through everted intestinal sacs was suppressed by dinitrophenol, anaerobiosis, absence of Na +, and by low temperatures.

Triglyceride biosynthesis from monoglycerides in isolated segments of intestinal mucosa Utilization of an ether analogue of 2-monostearin

1. 1. Triglyceride synthesis from monoglycerides was investigated during uptake by everted segments of rat small intestine. 2. 2. 1-Monoglycerides are converted into triglycerides via a 1,3-diglyceride intermediate. 1,2-Diglycerides are also formed during this conversion in varying amounts depending on the experimental conditions. This indicates the existence of an equilibrium between the 1,2- and 1,3-diglyceride isomers. It could not be ascertained whether 1,3-diglycerides are directly acylated to form triglycerides or are first isomerized to a 1,2-diglyceride. 3. 3. 2-Monoglycerides are converted to triglycerides via a 1,2-diglyceride intermediate. Indirect proof of this was achieved by using the ether analogue of 2-monostearin which was also taken up by the mucosa and esterified.

Intestinal Transport of Glucose and Sodium: Stimulation by Reserpine and the Humoral Mechanism Involved.

SummaryReserpine stimulates transport of glucose and Na by everted segments of rat small intestine. The drug is effective both in vivo and in vitro. Adrenal demedullation does not diminish the response to reserpine injections, but dichloroisoproterenol blocks the effects of reserpine. It is concluded that reserpine acts directly on the gut, and that its effects are at least in part consequent to release of catecholamines from storage sites in the intestine.

The absorption of vitamin B 12 in animals II. The site of absorption of vitamin B 12 and mode of action of intrinsic factor

1. 1. Radioactive vitamin B 12 was given by mouth to rats and baby pigs with and without binding and intrinsic factors. A few hours after dosing the greatest activity found in the wall of the gut was in the middle part of the small intestine and the area just distal to it. The amount of vitamin B 12 in this area of the intestine was increased by materials that promoted, and decreased by those that inhibited, absorption. 2. 2. A similar distribution in the gut wall was observed when vitamin B 12 with or without binding or intrinsic factors was circulated through the small intestine of live anaesthetized rats for 1 h. In these circumstances, however, greater amounts were found in the carcase when the vitamin had not been deposited in the gut wall. 3. 3. When similar perfusions were done with completely isolated small intestine of the rat the radioactivity that passed through the gut wall was all ultrafiltrable if rat stomach extract was in the circulating fluid. Only about 60% of the activity collected after perfusion with vitamin B 12 alone or with Bendogen was ultrafiltrable. 4. 4. Doses of labelled vitamin B 12 placed directly into the caeca of rats and pigs and the colon of pigs were very poorly absorbed. 5. 5. Preparations of mucosal cells from the middle segment of rat small intestine took up more vitamin B 12 on incubation at 38° than did similar preparations from the proximal or distal segments. Uptake of vitamin B 12 by the mucosal cells was enhanced by rat stomach extract and inhibited by Bendogen. 6. 6. Vitamin B 12 was detectable in the lymph collected from mesenteric or thoracic lymph ducts, but not in sufficient quantity to suggest that the lymphatic system is any more important a route of absorption than the blood stream

The uptake of amino acids by isolated segments of rat intestine II. A survey of affinity for uptake from rates of uptake and competition for uptake

Average rates have been determined for the uptake by segments of rat small intestine of 17 amino acids at the concentrations of I m M and IO m M. At IO m M the order is such that the more lipophilic amino acids show the smaller rates, but at I m M the order is distinctly reversed, with the more lipophilic amino acids having the greater rates. On the assumption that Michaelis-Menten kinetics apply to the rate of uptake, Michaelis constants have been calculated from the average rates at I m M and IO m M. From these constants, assuming that the amino acids compete for uptake by a Michaelis-Menten mechanism, predictions have been made of the effect of one amino acid on the other and have been compared with observed values. In general, the predictions agree well with the observed values, suggesting that the assumptions may be correct; but exceptions to the agreement suggest that L-lysine, and probably L-ornithine and L-arginine, may not compete for a common mechanism with the other L-amino acids. If the agreement is taken to implicate a rate-limiting, reversible combination with a common site in the uptake of most L-amino acids, then such a site shows a higher affinity for the more lipophilic amino acids. Limited studies with D-amino acids suggest that they may also combine with the site for uptake of L-amino acids, but have a lower affinity for it.

Distribution of intrinsic factor' activity.

After preincubation with hog intrinsic factor concentrate (HIFC), marked enhancement of Co60-labeled vitamin B12 uptake at 0°C by rat and human liver slices and by segments of rat small intestine was observable. No such marked enhancement by HIFC was observable in rat kidney, heart or spleen slices. After preincubation with serum from normal human beings or patients with pernicious anemia, slight enhancement of Co60-B12 uptake by rat liver slices was noted; marked enhancement was noted after preincubation with a 15-fold concentrate of normal human serum. The hypothesis is presented that there may exist a ‘circulating intrinsic factor’ involved in the selective deposition of vitamin B12 in the human liver.