Cholesterol reduces the effects of dihydroxy bile acids and fatty acids on water and solute transport in the human jejunum.

Jejunal perfusion studies were performed in 16 healthy volunteers to test the hypothesis that intraluminal cholesterol can mitigate the fluid secretion induced by dihydroxy bile acids and fatty acids. Fluid secretion in the presence of 5 mM taurodeoxycholate was somewhat reduced by 4 mM mono-olein which was used for the solubilization of cholesterol. Addition of 0.8 mM cholesterol reduced fluid secretion further (P less than 0.05). Fluid secretion induced by 4 mM oleic acid was changed to net absorption in a linear fashion with increasing cholesterol concentration in the perfusion solutions. 1 mM cholesterol reduced fluid secretion induced by 6 mM oleic acid (P less than 0.005), but had no effect on fluid secretion induced by 6 mM linolenic acid. Glucose absorption was generally affected in a similar manner as water transport. In vitro, 1 mM cholesterol reduced monomer activity of 6 mM oleic acid to 72.3 +/- 0.9% of control and that of linolenic acid to 81.1 +/- 1.7% of control. Although statistically significant (P less than 0.001), the difference in the effects of cholesterol on monomer activities of the two fatty acids was rather small and it is unlikely that changes in monomer concentration of fatty acids and bile acids account for the protective effect of cholesterol. The in vivo observations point to a new physiological role for biliary cholesterol: the modification of the response of the small intestine to the effects of dihydroxy bile acids and fatty acids.     

Role of bile acid conjugation in hepatic transport of dihydroxy bile acids

The effect of conjugation and side chain length on dihydroxy bile acid unidirectional hepatic uptake and efflux was studied using the isolated perfused rat liver which was perfused prograde or retrograde in single pass fashion. Deoxycholic acid (DC) and its C23 (nor) derivative nor-DC, as well as the synthetically prepared taurine conjugate of DC, were administered at a constant dose of 1 mumol/min/kg (body weight), upon which a bolus tracer dose of labeled bile acid was superimposed. Analysis of radioactivity recovery in perfusate indicated that unidirectional uptake of all three bile acids was equally rapid, but that only nor-DC showed considerable and continuing efflux into the perfusate; this involved mostly the unchanged acid. Nor-DC was not amidated but was metabolized to mostly ester glucuronides and hydroxylated derivatives; the biotransformation products did not reflux and were secreted into bile; similarly, DC was amidated with taurine; its taurine conjugate did not efflux and was secreted into bile. When nor-DC-taurine was infused, it did not efflux and was secreted rapidly into bile. When the liver was perfused retrograde fashion to increase concentrations of bile acids pericentral cells, only nor-DC showed efflux, which again involved only the unchanged acid. All bile acids were partly 7 alpha-hydroxylated, the magnitude being greater during retrograde perfusion presumably because slower cellular transport exposed bile acid to hydroxylation enzymes for a longer period. It is concluded that bile acid conjugation, whether by esterification with CoA formation adn subsequent amidation or by esterification with glucuronate, restricts the movement of lipophilic dihydroxy bile acids to the hepatocyte and canalicular lumen.(ABSTRACT TRUNCATED AT 250 WORDS)     

Metabolism of steroid and amino acid moieties of conjugated bile acids in man: II. Glycine-conjugated dihydroxy bile acids

Chenodeoxycholyl-2,4-(3)H-glycine-1-(14)C and deoxycholyl-2,4-(3)H-glycine-1-(14)C were synthesized and administered orally to 10 healthy subjects. Distribution of radioactivity among bile acids and specific activity of steroid and amino acid moieties were determined in bile samples. (3)H and (14)C were measured in feces. (14)C in breath was calculated from interval (14)CO(2) specific activity determinations.The daily fractional turnover of the glycine moiety of chenodeoxycholyl and deoxycholylglycines was more than three times that of the steroid moiety. Pool size of chenodeoxycholylglycine was about twice that of deoxycholylglycine, but similar fractional turnover rates of steroid and amino acid moieties suggested that intestinal absorption of the two conjugated bile acids was equally efficient (about 95%). The amount of unlabeled deoxycholic acid (newly formed by bacterial 7alpha-dehydroxylation) absorbed from the intestine approximated 30% of the cholic acid that was lost. (3)H radioactivity remained predominantly in administered bile acid implying that, normally, secondary bile acids derived from chenodeoxycholic acid are not appreciably absorbed from the intestine and that deoxycholic acid is not hydroxylated by the liver.Approximately 25% of administered (14)C was recovered in the breath in the first 24 hr and less than 8% in the feces in 8 days; (14)CO(2) excretion correlated highly with fractional turnover of the glycine moiety. (3)H appeared predominantly in feces, and the rate of excretion correlated highly with the fractional turnover of the steroid moiety of bile acids. From the results in this paper plus previous measurements on the metabolism of cholylglycine, we calculated that about 6 mmoles/day of glycine is used for bile acid conjugation in health.     

Effects of bile and bile acids on cultured human fibroblasts

Impaired healing induced by leakage of bile has been postulated as one factor responsible for complications after reconstructive bile duct surgery. The cytotoxicity of human bile and its major bile acids on cultured human fibroblasts was therefore studied by evaluation of their effects on cell morphology and growth, on synthesis and secretion of 35SO4-mucopolysaccharides and on release of a lysosomal enzyme. Normal human fibroblasts derived from a standard culture strain (MRC-5) were grown to confluence and exposed to: (1) sterile human T-tube bile, (2) a mixture of bile acids resembling that of human bile, or (3) various concentrations of the glycine- and taurine conjugates of cholic, chenodeoxycholic or deoxycholic acid. Medium containing whole bile (total bile acid concentration 0.25, 0.75 or 1.6 mmol/l) exerted time and dose dependent cytotoxic effects on morphology and growth and release of lysosomal enzyme. Synthesis and secretion of 35SO4-mucopolysaccharides were markedly inhibited. The bile acid mixture exhibited the same time and dose dependent effects. The conjugates of deoxycholic acid were found to be the most toxic of the individual bile acids studied.     

Actions of ricinoleic acid and structurally related fatty acids on the gastrointestinal tract. II. Effects on water and electrolyte absorption in vitro.

Ricinoleic acid, the active component of castor oil, and related fatty acids were studied to determine their relative inhibitory effects on water and electrolyte absorption using everted hamster jejunal and ileal segments. Differences were found between hydroxylated and nonhydroxylated congeners as well as between cis and trans geometric isomers. At a mucosal concentration of 2.0 mM, the unsaturated fatty acids had the following rank order of potency on inhibition of water absorption: ricionoleate greater than or equal to ricinelaidate- greater than equal to linoleate greater than oleate greater than linelaidate greater than elaidate. Ricinoleyl alcohol was effective at 2.0 mM but the methyl ester of ricinoleic acid was ineffective at this concentration. Among a series of saturated fatty acids including palmitate, stearate, a mixture of 9- and 10-hydroxystearate, and 12-hydroxystearate, only the last compound had any inhibitory effect on water absorption. The results define those portions of the ricinoleic acid molecule required for its effect on water and electrolyte absorption and suggest that classification of this cathartic as an "irritant" or "stimulant" should be re-evlauated.     

Absorption of short and medium chain fatty acids in the jejunum of the rat.

The uptake of the shortest six fatty acids (acetic to octanoic) was studied in vitro, using everted segments of rat jejunum. The marked influence of medium-pH and fatty acid chain-length suggests that non-ionic diffusion through the lipoid membrane is quantitatively the most important way of transport, but ionic diffusion through the membrane as well as transport through hydrophilic pores also seem to play a role. Though fatt acids evidently are accumulated in the tissue-fluid, and saturation kinetics, competitive inhibition and sodium- as well as energy-dependence apparently are observed, the transport mechanism is assumed to involve solely passive diffusion, - the concept of a carrier-mediated transport for short and medium chain fatty acids seems improbable.     

Arachidonic acid absorption in human jejunum in organ culture: effects of ethanol

Human jejunal tissue obtained by peroral biopsy was cultured in control medium and in medium containing 100 mmol l-1 ethanol. Subsequently, the incorporation and metabolism of [3H]-arachidonic and [14C]-linoleic acid were evaluated. Of the two fatty acids a significantly higher amount of [3H]-arachidonic acid was incorporated into phospholipids and more [14C]-linoleic acid was incorporated into triacylglycerols. This preferential distribution of the labelled fatty acids was not affected by ethanol, but when ethanol was present in the tissue culture medium, there was a significant decrease in the incorporation of both fatty acids into tissue phospholipids. The study thus shows that ethanol in moderate concentrations can affect human jejunal absorption and metabolism of polyenoic fatty acids, contributing to a decrease in the amount of eicosanoid precursors available in jejunal tissue.     

The effect of frusemide on water and electrolyte absorption from the human jejunum.

1. Frusemide, in a dose of 120 nmol (40 mg) administered intravenously, significantly reduced the absorption of water and electrolytes from the human jejunum, a double-lumen perfusion system with proixmal occluding balloons being used. Net secretion of water and electrolytes occurred in some subjects. 2. No significant change in water and electrolyte absorption was observed with 60 nmol (20 mg) of frusemide. 3. These findings may explain the diarrhoea which may be induced by fursemide in some patients.     

A study of relations between the absorption of amino acids, dipeptides, water and electrolytes in the normal human jejunum.

1. A double-lumen perfusion technique was used to study the effect of a wide range of concentrations of the dipeptide glycyl-L-alanine and its constituent amino acids on water and electrolyte absorption from iso-osmotic solutions in the upper jejunum of normal human subjects. 2. There was no significant absorption of water and electrolytes from sodium chloride solution (150 mmol/l) but the presence of the dipeptide or its constituent amino acids stimulated water and electrolyte absorption. 3. Water absorption reached a peak at increasing amino acid and dipeptide concentrations and then tailed off. Our data suggest that the tailing off is not solely due to the diminished sodium content of the solutions. 4. During perfusion of the dipeptide-sodium chloride and amino acid-sodium chloride solutions solute and water were absorbed as an iso-osmotic solution. Analysis of the results indicates that this could occur at high dipeptide concentrations only if the majority of the dipeptide enters the cell intact.     

Stimulation of active and passive sodium absorption by sugars in the human jejunum.

The effects of glucose and fructose on water and sodium absorption in the human jejunum were compared to assess the relative contribution of active and passive sugar stimulation of sodium transport. The effect of fructose is assumed to be entirely passive, and the difference between the effects of fructose and glucose is assumed to be a measure of sugar-stimulated, active sodium absorption. Water and sodium movement with mannitol was the base line. Three sets of test solutions with differing sugar concentrations were studied. Fructose stimulated 66-100 per cent as much net sodium and water absorption as glucose. Fructose stimulated potassium absorption, whereas glucose stimulated potassium secretion. Urea absorption was stimulated by both sugars. Glucose and fructose stimulated sodium absorption when chloride was the major anion, but they had relatively little effect on net sodium movement when chloride was replaced by bicarbonate or sulfate. It is concluded that glucose stimulates passive and active sodium transport in the human jejunum. Stimulated active sodium absorption generates an electrical potential across the mucosa that causes sodium (and potassium) secretion and partly or completely nullifies the effect of active sodium transport on net sodium movement. Net sodium absorption sitmulated by glucose is mainly (66-100 per cent) the passive consequence of solvent flow. The accompanying anion determines the degree to which sugars stimulate sodium absorption (C1 greater than SO-4 greater than HCO3). The effects of bicarbonate and sugars on jejunal sodium absorption are not additive.     

Effect of intraluminal hydrocortisone on solute and water absorption in the human jejunum

To compare the effects of intravenous and intraluminal hydrocortisone on jejunal transport, the proximal jejunum was perfused with glucose (28 mmol/l) in saline in two groups of normal subjects. In the first group of seven subjects, compared with the control period results there were no changes in sodium, water and glucose absorption during the intravenous administration of hydrocortisone. In contrast, intraluminal hydrocortisone (100 mg/l) increased sodium, water and glucose absorption by 169%, 223% and 81% respectively (P less than 0.001 in each case) above the control values, when peripheral plasma cortisol levels were similar to those achieved with intravenous hydrocortisone. In the second group of three subjects, intraluminal hydrocortisone (10 mg/l and 30 mg/l), followed by an intravenous infusion of hydrocortisone, had no effects on sodium, water and glucose absorption. In a third group of six normal subjects perfused with fructose (28 mmol/l) in saline and bicarbonate (28 mmol/l) in saline intraluminal hydrocortisone (100 mg/l) had no effect on solute and water absorption. These results suggest that intraluminal hydrocortisone stimulates glucose-coupled sodium transport by exerting a topical effect on the apical membrane of the jejunal mucosa.     

Regulation of pancreatic and gallbladder functions by intraluminal fatty acids and bile acids in man.

The effects of intraduodenal glycerol, fatty acid (FA) chain length and FA loads, and bile acid (BA) concentrations on pancreatic and gallbladder function were investigated in 31 healthy volunteers by a perfusion method. FA absorption rates in the duodenum and proximal jejunum were measured simultaneously. Pancreatic and gallbladder responses were augmented by increasing FA chain length and FA loads until the "maximal" secretory capacity of the pancreas and gallbladder emptying was attained. Glycerol had no effect. Raising BA concentrations above the critical micellar concentration accelerated FA absorption rates but decreased the magnitude of pancreatic and gallbladder responses to FA. Higher BA concentrations exerted an opposite effect, slowing FA absorption and increasing pancreatic and gallbladder responses. Indeed, a significant, inverse correlation was found between FA absorption and pancreatic and gallbladder responses to FA, suggesting a relationship between the length of intestine exposed to FA and the amount of cholecystokinin (and/or other neurohormonal factors) released, which stimulates pancreatic secretion and gallbladder contraction.