The absorption of phenformin and its effects on glucose and water absorption in isolated perfused rat small intestine

The effects of phenformin on glucose and water absorption from isolated perfused rat small intestine were studied. Luminal phenformin inhibited glocose and water absorption progressively as its concentration was increased from 0-1-1-0 mg.ml-1. At 0-5 mg phenformin ml-1, inhibition increased with time of exposure to phenformin up to 15 min and thereafter remained constant. Arterial infusion of phenformin (1-0 mg-ml-1) produced less inhibition of glucose and water absorption. The site of phenformin's action appeared to be intracellular. Phenformin absorption from a luminal perfusate (0-5 mg-ml-1) was measured. Although it was rapidly absorbed (22 microgram.cm intestine-1.h-1) from the lumen, less than 2 microgram.cm-1.h-1 appeared at the serosal surface of the intestine. In subsequent phenformin-free perfusion, only 25% of the absorbed phenformin was recovered in the luminal and serosal effluents.     

Difructose anhydrides III and IV equally promote calcium absorption from the luminally perfused rat small intestine

We examined the effects of di-D-fructose anhydride (DFA) III and IV on Ca absorption in luminally perfused segments of the small intestine in anesthetized rats. The calcium absorption rate with perfusion of 10 mmol/l CaCl2 was similarly increased by addition of 100 mmol/l DFAIII or IV, and these promotive effects of both DFAs were pronounced at perfusion rate of 0.15 ml/min than at 0.3 ml/min. The promotive effects were higher in the duodenojejunum than in the ileum.     

Efficacy of perfluorodecalin as an oxygen carrier for mouse and rat testes perfused in vitro

Perfluorodecalin is a superior artificial oxygen carrier because of its high oxygen dissolving capacity, low toxicity, and short retention times within tissues. However, the instability of perfluorodecalin emulsions has hindered its application in blood substitutes. The present study addressed two questions. First, is perfluorodecalin deleterious to the endocrine function of testes? This question was examined by comparing testosterone secretion by testes perfused in vitro with medium incorporating either perfluorodecalin or erythrocytes as oxygen carriers. Second, can stable emulsions of perfluorodecalin be attained with the new surfactant Butronic U-1? This question was approached by determining the stability of perfluorodecalin emulsions containing either Butronic U-1 or Pluronic F-68, a proven ineffective surfactant. The experimental results support the efficacy of perfluorodecalin emulsions as oxygen carriers for mouse and rat testes perfused in vitro. Perfluorodecalin emulsions formed with Butronic U-1 were stable during the 4-hr perfusions but not during long-term storage.     

Stimulation of glutathione absorption in rat small intestine by alpha-adrenergic agonists.

The alpha-adrenergic agonist, phenylephrine (1.6 microM), caused a threefold stimulation of glutathione (GSH) transport from the lumen into the vasculature in isolated, vascularly perfused rat small intestine. Stimulation of GSH transport by phenylephrine was blocked by the alpha-adrenergic antagonists, prazosin or phentolamine. Norepinephrine and epinephrine (both alpha and beta agonists) also stimulated GSH absorption but not to the same extent as phenylephrine. Isoproterenol, a strict beta-adrenergic agonist, had no effect on the rate of GSH absorption. Under physiological luminal GSH concentrations, phenylephrine stimulated GSH efflux from the lumen, accumulation in the intestinal mucosa, and transport into the mesenteric vasculature. Phenylephrine did not stimulate the transport of polyethylene glycol, a high molecular weight molecule, and stimulated uptake of cysteine and glycine by 30%. This suggests that the effect of phenylephrine on GSH transport is not due to enhanced bulk flow through paracellular pathways. Studies with isolated small intestinal epithelial cells showed that phenylephrine also stimulated the release of GSH from the cells. Oral administration of phenylephrine with GSH caused a two- to fivefold transient increase in plasma GSH concentrations in rats. Phenylephrine alone or with the amino acid constituents of GSH caused no increase in plasma GSH concentration. Thus, absorption of dietary GSH is under hormonal regulation. The physiological importance of this regulation is not known, although such regulation may function to control utilization of dietary GSH for detoxication and may have therapeutic benefits for individuals with deficient GSH or increased risk of oxidative or chemically induced injury.     

Studies of albumin binding to rat liver plasma membranes. Implications for the albumin receptor hypothesis

To characterize a previously proposed hepatocyte albumin receptor, we examined the binding of native and defatted 125I-labeled rat albumin to rat liver plasma membranes. After incubation for 30 min, binding was determined from the distribution of radioactivity between membrane pellet and supernatant following initial centrifugation (15000 X g for 15 min), and after repeated cycles of washing with buffer and re-centrifugation. 125I-labeled albumin recovered in the initial membrane pellet averaged only 4% of that incubated. Moreover, this albumin was only loosely associated with the membrane, as indicated by recovery in the pellet of under 0.5% of the counts after three washes. Binding of 125I-labeled albumin to the plasma membranes was no greater than to erythrocyte ghosts, was not inhibited by excess unlabeled albumin, and was not decreased by heat denaturation of the membranes, all suggestive of a lack of specific binding. Failure to observe albumin binding to the membranes was not due to a rapid dissociation rate or 'off-time', as incubations in the presence of sufficient ultraviolet light to promote covalent binding of ligands to receptors did not increase 125I counts bound to the membrane. Finally, affinity chromatography over albumin/agarose gel of solubilized membrane proteins provided no evidence of a membrane protein with a high affinity for albumin. These studies, therefore, do not support the hypothesis that liver cell plasma membranes contain a specific albumin receptor.     

Paracellular absorption of D-glucose by rat small intestine in vivo

D-glucose diffusion in both jejunum and ileum using a perfusion system in vivo was determined. 2,4,6-triaminopyrimidine (20 mM) induced an inhibition on D-glucose diffusion of 32% in the two segments of the small intestine studied. Glucose net efflux from the jejunum into the lumen was higher than that from the ileum. Phlorizin increased the sugar efflux in both areas.     

The effects of amino acids on albumin synthesis by the isolated perfused rat liver

Albumin synthesis was measured in the isolated perfused rat liver by using the livers of both well-fed and starved rats. Starvation markedly decreased albumin synthesis. The livers from starved rats were unable to increase synthesis rates after the addition to the perfusates of single amino acids or the addition of both glucagon and tryptophan. Arginine, asparagine, isoleucine, leucine, lysine, methionine, phenylalanine, proline, threonine, tryptophan and valine, added together to ten times their normal peripheral blood concentrations, restored synthesis rates to normal. The plasma aminogram (i.e. the relative concentrations, of amino acids) was altered by depriving rats of protein for 48h. The use of blood from the deprived rats as perfusate, instead of normal blood, decreased albumin synthesis rates significantly by livers obtained from well-fed rats. The addition of single amino acids, including the non-metabolizable amino acid, alpha-aminoisobutyric acid, to the above mixture increased albumin synthesis rates to normal values. It is concluded that amino acids play an important role in the control of albumin synthesis and that more than one mechanism is probably involved.     

Kinetics of the absorption of amino acids by the rat intestine in vivo

The kinetics of l-phenylalanine and l-lysine absorption by the rat small intestine in vivo have been studied by perfusing intestinal segments and monitoring simultaneously the uptake of the substrate into the intestinal tissue and its disappearance from the perfusate.The rate of phenylalanine disappearance is a linear function of the substrate concentration. Its uptake into the tissue is rapid and obeys saturation kinetics, but is not concentrative. Both tissue uptake and disappearance rate can be inhibited by leucine or methionine, but are not influenced by hydrophilic neutral or dibasic amino acids.Lysine disappearance from the perfusate and its uptake into the tissue both display saturation kinetics. Lysine transport is quantitatively smaller than that of phenylalanine. Both uptake and disappearance are inhibited by arginine and leucine, but are unaffected by other neutral amino acids or sugars.To analyse the kinetic results, integrated equations were developed to express the final concentration in the perfusate in terms of the original concentration. The disappearance rate was considered as a mixed process (saturable and non-saturable in parallel) in a one-compartment system, and the uptake by the tissue was treated as a two-compartment system in which the amino acid entered the cells by a mixed process but left them by a pure non-saturable mechanism.The results concerning disappearance from the lumen are compatible with the one-compartment model. Phenylalanine absorption can be described by a major non-saturable component and a minor saturable one, while lysine absorption occurs almost entirely by a saturable process. The two-compartment model does not adequately describe the tissue uptake results.     

Quantitation of zinc in nitric acid-digested plasma by atomic absorption spectrophotometry

Human plasma, digested in a screw-capped Teflon vial for 1 h at 130 degrees C in concentrated nitric acid, is assayed for zinc by atomic absorption spectrophotometry using a single-slot, 10-cm burner and air/acetylene flame. The assay is linear to 10.00 mg Zn/liter, recovery averages 100.9%, and inter- and intraassay coefficients of variation are 5.9 and 1.9%. With this method, there is no burner clogging or adjustment necessary for sample viscosity. Sodium chloride does not interfere with the assay. The linear regression data of the standard curve for milligrams of Zn per liter (x) and milliabsorbance units (y) is y = 40x + 0.001.     

Intestinal absorption in the mechanically obstructed rat intestine: protection by prostaglandins

Intestinal obstruction inhibits amino acid absorption. The inhibition, being dependent on the pathological changes of the absorptive epithelium, was considered as an index of injury and measured after varying periods of obstruction and after pretreatment with clindamycin, indomethacin, 16,16-dimethyl-PGE2 or arachidonic acid. A reduction in amino acid uptake was apparent after 2h of obstruction and was increasingly evident after 4, 6 and 18 h. During the late phase (after 6 h), inhibition was partly prevented by pretreatment with clindamycin, but the antibiotic was ineffective during the early phase (within the first 2 h). Bacterial colony counts of luminal contents of rats obstructed for 2 h, were not different from counts obtained in controls, but significantly lower than counts in rats that have been obstructed for 6 h. Pretreatment of rats with 16,16-dimethyl-PGE2 or with arachidonic acid prevented the early inhibitory effects of the obstruction. The findings suggest that the early inhibition in amino acid uptake may be related to metabolic changes that are correctable by the administration of 16,16-dimethyl-PGE2 or of arachidonic acid. The inhibition, during the late phase, is mainly related to an overgrowth of the enteric bacteria.