Further studies on the properties of bile acids. I. Bile acid-induced changes of the action of drugs acting on the autonomic nervous system on the heart and blood vessels

The action of certain drugs on the autonomic system was studied under the influence of bile acids: 3,12-dihydroxycholanic acid (deoxycholic), 3,7,12-trihydroxycholanic acid (cholic), and 3,7,12-triketocholanic acid (dehydrocholic). The experiments were carried out on rat heart in vivo and on isolated rat vessel preparation. It was shown that bile acids reduced the stimulating effect of isoprenaline on rat heart and the relaxing effect on the blood vessels. An inversion of the effects of adrenaline and noradrenaline on the rat heart was observed, and an enhancement of the vasoconstrictor effect of these substances. Under the conditions of this experiment an inversion was noted of the action of acetylcholine on the heart and blood vessels.     

Prejunctional alpha 2 adrenoceptors inhibit contraction of tracheal smooth muscle by inhibiting cholinergic neurotransmission

Ring preparations obtained from the guinea pig trachea contracted on short trains of electrical field stimulation. These contractions were mediated by activation of cholinergic nerves since they were abolished by atropine or tetrodotoxin. In the presence of beta blocking drugs noradrenaline and adrenaline dose-dependently inhibited contractions induced by field stimulation. By contrast, contractions on exogenous acetylcholine were left completely unaffected. It is concluded that the adrenergic agonists inhibited cholinergic neurotransmission by a prejunctional action. In order to characterize the noradrenaline receptor the effects of alpha₁ and alpha₂ blockers were evaluated using the Schild plot. For comparison experiments were also conducted on the guinea pig aorta and electrically stimulated guinea pig ileum. The results indicate that in guinea pig trachea and ileum noradrenaline inhibits cholinergic neurotransmission by acting on prejunctional alpha₂ receptors whereas in guinea pig aorta it induces contraction by stimulating alpha₁ receptors.     

Differential control of glycogenolysis and flow by arterial and portal acetylcholine in perfused rat liver.

The effects of acetylcholine on glucose and lactate balance and on perfusion flow were studied in isolated rat livers perfused simultaneously via the hepatic artery (100 mmHg, 25-35% of flow) and the portal vein (10 mmHg, 75-65% of flow) with a Krebs-Henseleit bicarbonate buffer containing 5 mM-glucose, 2 mM-lactate and 0.2 mM-pyruvate. Arterial acetylcholine (10 microM sinusoidal concentration) caused an increase in glucose and lactate output and a slight decrease in arterial and portal flow. These effects were accompanied by an output of noradrenaline and adrenaline into the hepatic vein. Portal acetylcholine elicited only minor increases in glucose and lactate output, a slight decrease in portal flow and a small increase in arterial flow, and no noradrenaline and adrenaline release. The metabolic and haemodynamic effects of arterial acetylcholine and the output of noradrenaline and adrenaline were strongly inhibited by the muscarinic antagonist atropine (10 microM). The acetylcholine-dependent alterations of metabolism and the output of noradrenaline were not influenced by the alpha 1-blocker prazosin (5 microM), whereas the output of adrenaline was increased. The acetylcholine-dependent metabolic alterations were not inhibited by the beta 2-antagonist butoxamine (10 microM), although the overflow of noradrenaline was nearly completely blocked and the output of adrenaline was slightly decreased. These results allow the conclusion that arterial, but not portal, acetylcholine caused sympathomimetic metabolic effects, without noradrenaline or adrenaline being involved in signal transduction.     

The effect of bile, bile acids and detergents on calcium absorption in the chick

1. Bile from rachitic or normal chicks causes an immediate increase in the intestinal absorption of soluble calcium in rachitic and vitamin D(3)-treated chicks as tested in vivo by intestinal-loop and oral-dosing methods. 2. This effect is apparently solely due to the taurine-conjugated bile acids present in the bile and is independent of the action of vitamin D. 3. Chick bile and bile acids can increase the solubility and the absorption of calcium presented as sparingly soluble calcium hydrogen phosphate. 4. In addition, bile is necessary to some extent at least for the intestinal absorption of vitamin D(3) in the chick and this would indirectly enhance the absorption of calcium. 5. Thus bile is capable of a threefold action in the absorption of calcium in the chick. It is suggested that the direct action on sparingly soluble forms of calcium is of considerable physiological importance since most of the calcium in the normal bird's diet would be in this form. 6. Bile acids enhance the absorption of calcium in all regions of the small intestine of the chick. 7. Of a range of bile acids and detergents tested for enhancement of calcium absorption, various taurine-conjugated bile acids and sodium lauryl sulphate, an anionic detergent, are effective. A non-ionic detergent (Tween 80) and a cationic detergent (Zephiran) are without effect. 8. The ability of a substance to increase directly the intestinal absorption of soluble calcium appears to depend to some extent on an anionic detergent action, i.e. the ability to form a salt or complex soluble to some extent in both aqueous and lipid phases. 9. In chicks the immediate deposition of calcium ((45)Ca) in the bones closely reflects any increase in plasma calcium radioactivity regardless of the cause of the increase and regardless of the vitamin D(3) status. Although sodium lauryl sulphate can increase markedly the calcium absorption from the gut and the immediate deposition in the bones it has no significant effect on rickets. 10. Some of the implications of these findings are discussed.     

The action of parotoid venom on the heart of the toad (Bufo ictericus ictericus Spix 1824) and its effects on the inhibition caused by vagal stimulation

1. The administration of crude venom of the parotoid glands of the toad Bufo ictericus ictericus to the in situ (via abdominal vein) or isolated heart of this anuran causes both chronotropic and inotropic effects. 2. While under action of parotoid venom, the heart of the animal is insensitive to vagus nerve stimulation. 3. This blocking of vagal action is dose dependent and it is suggested that it results from a functional antagonism between the venom constituents and the acetylcholine liberated by the nerve endings on stimulation. 4. The venom constituents probably involved in this antagonism are catecholamines (adrenaline and noradrenaline), tryptamine derivatives (serotonin and bufotenidin) and genins (bufagin and bufotoxin), possibly also ATP. 5. Adrenaline, noradrenaline and serotonin, or a mixture of the three, mimic, at least partially, the blocking of vagal action caused by crude venom. 6. The blocking action of crude venom can be prevented by previously or simultaneously adding acetylcholine to the infused crude venom. This prevention is dose dependent. 7. The blocking action persists in the boiled venom and in the material dialysed from crude venom.     

Influence of dietary bile acids on formation of bile acids in rat

Various taurine-conjugated bile acids were fed to rats at the 1%-level in the diet for 3 or 7 days and the effect on several hydroxylations involved in the biosynthesis and metabolism of bile acids was studied. The hydroxylations studied were all catalyzed by the microsomal fraction of liver homogenate fortified with NADPH. The 7α-hydroxylation of cholesterol was inhibited by feeding taurocholic acid, taurocheno-deoxycholic acid and taurodeoxycholic acid for 3 as well as 7 days. No marked inhibition was obtained with taurohyodeoxycholic acid or taurolithocholic acid. The 12α-hydroxylation of 7α-hydroxy-4-cholesten-3-one was inhibited after 3 as well as 7 days by all bile acids except taurohyodeoxycholic acid. With this acid a marked stimulation of 12α-hydroxylation was observed. The effects of the different bile acids on the 7α-hydroxylation of taurodeoxycholic acid were not very marked. The 6β-hydroxylation of lithocholie acid and taurochenodeoxycholic acid was stimulated by taurocholic acid and taurodeoxycholic acid. The reaction was inhibited by taurochenodeoxycholic acid, at least after 7 days. Taurohyodeoxycholic acid inhibited the 6β-hydroxylation slightly and taurolithocholic acid had no effect. The results were discussed in the light of present knowledge concerning mechanisms of regulation of formation and metabolism of bile acids and it was suggested that the mechanisms may be more complex than previously thought.     

Improved suppression by dietary taurine of the fecal excretion of bile acids from hypothyroid rats.

The effect of dietary taurine, 2-aminoethanesulfonic acid, on hypercholesterolemia caused by thiouracil-induced hypothyroidism was investigated in hypothyroid rats. Serum total- and HDL-cholesterol were significantly increased, and the excretion of fecal bile acids was significantly decreased. Taurine did not change the hypercholesterolemia, but significantly recovered the excretion of bile acids.     

Effects of bile acids on the muscle functions of guinea pig gallbladder

Hydrophobic bile acids impair gallbladder emptying in vivo and inhibit gallbladder muscle contraction in response to CCK-8 in vitro. This study was aimed at determining the mechanisms of muscle cell dysfunction caused by bile acids in guinea pig gallbladders. Muscle cells were obtained by enzymatic digestion. Taurochenodeoxycholic acid (TCDC), a hydrophobic bile acid, caused a contraction of up to 15% and blocked CCK-induced contraction. Indomethacin abolished the TCDC-induced contraction. Hydrophilic bile acid tauroursodeoxycholic acid (TUDC) had no effect on muscle contraction but prevented the TCDC-induced contraction and its inhibition on CCK-induced contraction. Pretreatment with NADPH oxidase inhibitor PH2I, xanthine oxidase inhibitor allopurinol, and free-radical scavenger catalase also prevented TCDC-induced contraction and its inhibition of the CCK-induced contraction. TCDC caused H2O2 production, lipid peroxidation, and increased PGE2 synthesis and activities of catalase and SOD. These changes were significantly inhibited by pretreatment of PH2I or allopurinol. Inhibitors of cytosolic phospholipase A2 (cPLA2), protein kinase C (PKC), and mitogen-activating protein kinase (MAPK) also blocked the TCDC-induced contraction. It is concluded that hydrophobic bile acids cause muscle cell dysfunction by stimulating the formation of H2O2 via activation of NADPH and xanthine oxidase. H2O2 causes lipid peroxidation and activates cPLA2 to increase PGE2 production, which, in turn, stimulates the synthesis of free-radical scavengers through the PKC-MAPK pathway.     

Enhancement of the autocatalytic activation of trypsinogen to trypsin by bile and bile acids

The activation of trypsinogen to trypsin in the small intestine can occur by the action of enterokinase or, alternatively, as an autocatalytic process catalysed by trypsin itself. We have found that bile salts and human bile cause a significant enhancement of the autocatalytic activation of trypsinogen. This effect is dependent on the calcium ion concentration and is most marked around pH 5.4 and 7.8. An optimum concentration exists for each bile salt at which the greatest enhancement occurs. At this concentration, certain bile salts have been shown to produce activation effects of up to 55-fold. It is suggested that this activation of the autocatalytic process by bile plays an important role in protein digestion in the small intestine, since it has been shown previously that duodenal trypsin levels are abnormally low in patients with an impairment of bile secretion.     

Differential regulation of cytosolic and peroxisomal bile acid amidation by PPAR alpha activation favors the formation of unconjugated bile acids

In human liver, unconjugated bile acids can be formed by the action of bile acid-CoA thioesterases (BACTEs), whereas bile acid conjugation with taurine or glycine (amidation) is catalyzed by bile acid-CoA:amino acid N-acyltransferases (BACATs). Both pathways exist in peroxisomes and cytosol. Bile acid amidation facilitates biliary excretion, whereas the accumulation of unconjugated bile acids may become hepatotoxic. We hypothesized that the formation of unconjugated and conjugated bile acids from their common substrate bile acid-CoA thioesters by BACTE and BACAT is regulated via the peroxisome proliferator-activated receptor alpha (PPARalpha). Livers from wild-type and PPARalpha-null mice either untreated or treated with the PPARalpha activator WY-14,643 were analyzed for BACTE and BACAT expression. The total liver capacity of taurochenodeoxycholate and taurocholate formation was decreased in WY-14,643-treated wild-type mice by 60% and 40%, respectively, but not in PPARalpha-null mice. Suppression of the peroxisomal BACAT activity was responsible for the decrease in liver capacity, whereas cytosolic BACAT activity was essentially unchanged by the treatment. In both cytosol and peroxisomes, the BACTE activities and protein levels were upregulated 5- to 10-fold by the treatment. These effects caused by WY-14,643 treatment were abolished in PPARalpha-null mice. The results from this study suggest that an increased formation of unconjugated bile acids occurs during PPARalpha activation.     

Intestinal microflora and bile acids. Effect of bile acids on the distribution of microflora and bile acid in the digestive tract of the rat

The population levels of intestinal microflora and bile acid composition in the digestive tract were examined in rats fed bile acids to determine the relationships between gastrointestinal microflora and the host. The population level of Bacteroides was increased in the ceca of rats fed cholic acid or deoxycholic acid. In the ileum, the concentration of conjugated bile acid in rats fed cholesterol, cholic acid, hyodeoxycholic acid or lithocholic acid was higher than that in control rats, and was very low in ceca and feces of all the rats. The concentration of total free bile acid was much higher in the ceca than in the ilea of rats fed hyodeoxycholic acid or lithocholic acid. Cholic acid and deoxycholic acid were found in the ilea, ceca and feces of the cholic acid-fed rats. In the deoxycholic acid-fed rats, cholic acid was localized in the ileum. 7-Ketodeoxycholic acid was also found in the ceca of the cholic acid-fed rats. 12-Ketolithocholic acid was found in the feces of rats fed cholic acid or deoxycholic acid. 3-Ketocholanic acid was found in some samples from the lithocholic acid-fed rats. Therefore, some kinds of bile acids influence the population levels of gastrointestinal microflora and bile acid composition in the intestine.     

Neurotransmitters in the intestine of the Atlantic cod, Gadus morhua

The effects of the putative neurotransmitters acetylcholine, adrenaline, adenosine, ATP, bombesin, 5-hydroxytryptamine, met-enkephalin, neurotensin, somatostatin, substance P and VIP have been investigated in the perfused intestine of the cod, Gadus morhua. The presence and distribution of the different types of nerves was investigated with immunohistochemistry and Falck-Hillarp fluorescence histochemistry. A spontaneous rhythmic activity of the perfused preparations usually occurred within a few minutes from the start of the experiment. This activity was diminished or abolished by addition of atropine, methysergide or tetrodotoxin to the perfusion fluid. Acetylcholine, 5-hydroxytryptamine or substance P caused a contraction of the intestinal wall. The response to acetylcholine was blocked by atropine but not by tetrodotoxin, while the response to 5-hydroxytryptamine was blocked by methysergide and usually also by tetrodotoxin. This indicates that the effect of acetylcholine is direct on the muscle cells, while the effect of 5-hydroxytryptamine may be at least partly via a second neuron. All adrenergic agonists (adrenaline, isoprenaline and phenylephrine) had a dominating inhibitory effect on the intestine. Experiments with antagonists showed that the inhibition is due to stimulation of both alpha-adrenoceptors and beta-adrenoceptors. ATP, adenosine and somatostatin also caused a relaxation of the intestinal wall, often followed by a contraction. Met-enkephalin produced variable responses, either a relaxation, a contraction or both. Bombesin caused a weak inhibition, if anything. Neurotensin and VIP did not visibly affect the intestinal motility. 5-HT-, substance P- and VIP-like immunoreactivity and catecholamine fluorescence were observed in the myenteric plexus, submucosa and muscle layers in all parts of the intestine.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effect of blood flow and muscle contraction on noradrenaline spillover in the canine gracilis muscle

Many authors have reported that, during exercise, noradrenaline spillover increases and fractional extraction decreases. It has been suggested that the increase in blood flow to active muscles may contribute to these effects. Muscle contraction also causes changes in many factors that may affect noradrenaline spillover and fractional extraction. In this experiment, we studied the effect of muscle contraction and blood flow on noradrenaline and adrenaline spillover and fractional extraction in the in situ canine gracilis muscle. The low intensity stimulation protocol enabled us to have muscle contractions without any effect on the local concentration of noradrenaline, as measured by microdialysis, and noradrenaline spillover. Fractional extraction of both noradrenaline and adrenaline was unaffected by increasing blood flow three and four times its resting value. In addition, noradrenaline spillover was increased by the higher blood flow, from 188 to 452 pg x min(-1) at rest and from 246 to 880 pg x min(-1) during stimulation. Stimulation of muscle contraction caused a significant increase in fractional extraction of noradrenaline and a nonsignificant increase in adrenaline extraction. In addition, an adrenaline spillover was observed in certain conditions. In light of our results, it seems that blood flow may not be the main factor decreasing fractional extraction of noradrenaline during exercise. However, blood flow could contribute to the increase in noradrenaline spillover observed in the active muscles during exercise.     

Bile acids in the rat: studies in experimental occlusion of the bile duct

Bile acids in the plasma, urine, and small intestine of adult male rats with occluded bile ducts have been studied using a method of high specificity for their determination. After bile duct ligation cholic acid rapidly accumulates in the plasma for 8 hr, remains high for a further 8 hr, and subsequently diminishes; bile acids disappear from the small intestine. During the first 12 hr after bile duct ligation the excretion of trihydroxy acids in the urine was 10 times that of the dihydroxy acids. Subsequently the two excretion rates became equal. Because bile acids have been implicated in the etiology of hepatic damage following bile duct ligation, studies have been made of the effect on the liver of removing (with cholestyramine) and supplementing (with cholic acid) the intestinal bile acid pool. The addition of cholestyramine to the stock diet prevented the rise in trihydroxy bile acids after bile duct ligation, but did not prevent the development of histological abnormalities in the liver. Supplementing the diet with cholic acid raised the plasma cholic acid levels but had little effect on the hepatic histological findings.     

Interaction of gut microbiota with dysregulation of bile acids in the pathogenesis of nonalcoholic fatty liver disease and potential therapeutic implications of probiotics

The intestinal microbiota is now recognised to play key roles in health due to its involvement in many aspects of human physiology. Disturbance in gut microbiota (dysbiosis) is thus associated with many diseases including nonalcoholic fatty liver disease (NAFLD) which includes nonalcoholic fatty liver and nonalcoholic steatohepatitis. The mechanisms for the effect of dysbiosis in NAFLD pathogenesis are not completely elucidated. Many explanations have been proposed to trigger dysbiosis, leading to NAFLD including inflammation, ethanol produced by the gut bacteria and lipotoxicity. Recently the roles of bile acids and nuclear receptors are highly regarded. It is well known that gut microbes produce enzymes that convert primary bile acids into secondary bile acids in the intestines. Several studies have demonstrated that disturbance of the intestinal microbiota leads to decreased synthesis of secondary bile acids, which in turn decreases activation of nuclear receptors such as farnesoid X receptor (FXR), pregnane X receptor, Takeda G-protein–coupled bile acid protein 5 and vitamin D receptor. These receptors are important in energy regulation and their dysregulation can cause NAFLD. Therefore, stimulation of nuclear receptors especially FXR has been extensively explored for the amelioration of NAFLD. However, paradoxical effects of nuclear receptor activation are a major problem for the clinical application of nuclear receptor stimuli. We further posit that microbiome restoration could be an alternative approach for the treatment of NAFLD. Several gut bacteria are now known to be involved in bile acid metabolism. It will be necessary to identify which one/ones is/are feasible. Careful selection of commensal bacteria for probiotics may lead to an effective therapy for NAFLD.     

Radioprotective action of catecholamines on a Chinese hamster fibroblast culture

The radioprotective ability of adrenaline, noradrenaline and isoproterenol in various concentrations has been studied in experiments on cultured Chinese hamster fibroblasts in vitro. Radioprotective effect of isoproterenol is pronounced at 10(-8)M concentration; adrenaline and especially noradrenaline are effective at higher concentrations. The antagonist of beta-adrenergic receptors propranolol blocks the radioprotective effect of catecholamines on cells. The beta-adrenergic mechanism of catecholamines radioprotective action on the mammals cells is under discussion.     

Sterol and bile acid metabolism during development. 1. Studies on the gallbladder and intestinal bile acids of newborn and fetal rabbit

Bile acid composition and content in the intestine and gallbladder of newborn and fetal rabbits were investigated. Unlike the circumstances in adult rabbits, the bile acids were conjugated with both taurine and glycine. The major bile acids of the fetus and newborn rabbit were cholic acid, chenodeoxycholic acid, and deoxycholic acid. This is different from the known bile acid composition of adult rabbits, in which deoxycholic acid is the major bile acid (> 80%). The proportion of chenodeoxycholic acid was higher in the fetal than in the newborn tissues. The total bile acid pool in the newborn was higher than in the fetus. In the fetus, large proportions of bile acids (60.9%) were associated with the gallbladder fraction, whereas in the newborn the bulk of the bile acids were found with the intestinal fraction (64.4%),