Acid Metabolism In Rats Research Articles

Effects of beta-lactam antibiotics on intestinal microflora and bile acid metabolism in rats.

Wistar male rats were treated for six days with broad spectrum beta-lactam antibiotics, latamoxef, and cefotaxime. On the seventh day, the number of fecal anaerobic microbes decreased, total fecal bile acids decreased, and bile acid pools increased. Secondary bile acids such as beta-hyocholic, hyodeoxycholic, lithocholic, and deoxycholic acids decreased in the feces while the primary bile acids, cholic, beta-muricholic, and chenodeoxycholic acids, became predominant. Coprostanol, a microbial metabolite of cholesterol, also disappeared from the feces during the treatment. The cecum enlarged to almost twice the size of that in control rats, whereas the liver weight was not significantly changed. After treatment was stopped, the number of fecal microbes returned to the initial counts within a week, but restoration of bile acid and cholesterol metabolism required at least three weeks.

Arachidonic acid metabolism in galactosamine/endotoxin induced acute liver injury in rats.

The changes of the levels of LTC4, PGI2 and TXA2 in the liver tissue in SD rats with GaIN/LPS-induced acute liver injury was studied with radioimmunoassay (RIA). As a result, 12 h after the administration of GaIN/LPS, serum AST (398 +/- 37 u), ALT (565 +/- 43 u) increased (P < 0.001) and the concentration of TXA2 (12,188 +/- 588 pg/g.w.wt) in liver tissue increased significantly (P < 0.001), while the content of LTC4 (9713 +/- 3557 ng/g.w.wt) and PGI2(1748 +/- 560 pg/g.w.wt) in liver tissue were not obviously changed (P > 0.05) and the inflammatory changes of the pathological findings were observed. The improvement of serum ALT (330 +/- 168 u) (P < 0.05) and AST (273 +/- 124 u) (P < 0.05) and histopathological damage was observed after the administration of diethylcarbamazine (DEC), a LTA4 synthesis inhibitor, the liver TXA2 (12,740 +/- 699) concentration significantly increased (P < 0.001), while the levels of LTC4 (8179 +/- 1653) and PGI2 (2320 +/- 630) were not obviously changed. Serum ALT (536 +/- 74 u) and AST (416 +/- 41 u) (P > 0.05) levels and histopathology did not change with administration of indomethacin, a cyclooxygenase inhibitor, but the liver LTC4 (12,166 +/- 1327) contents increased (P < 0.05) and TXA2 (1868 +/- 791) reduced significantly (P < 0.001). The present study suggests that arachidonic acid metabolism in rats with acute liver injury are significantly abnormal. Leukotrienes and thromboxane are important inflammatory mediators in the liver injury.

Mechanisms of impaired hepatic fatty acid metabolism in rats with long-term bile duct ligation.

Hepatic metabolism of fatty acids is impaired in experimental animals with long-term bile duct ligation. To characterize the underlying defects, fatty acid metabolism was investigated in isolated hepatocytes and isolated liver mitochondria from rats subjected to long-term bile duct ligation or sham surgery. After starvation for 24 hr, the plasma beta-hydroxybutyrate concentration was decreased in rats with bile duct ligation as compared with control rats. Production of beta-hydroxybutyrate from butyrate, octanoate and palmitate by hepatocytes isolated from rats subjected to bile duct ligation was also decreased. Liver mitochondria from rats subjected to bile duct ligation showed decreased state 3 oxidation rates for L-glutamate, succinate, duroquinone, and fatty acids but not for ascorbate as substrate. State 3u oxidation rates (uncoupling with dinitrophenol) and activities of mitochondrial oxidases were also decreased in mitochondria from rats subjected to bile duct ligation. Direct assessment of the activities of the subunits of the electron transport chain revealed reduced activities of complex I, complex II and complex III in mitochondria from rats subjected to bile duct ligation. Activities of the beta-oxidation enzymes specific for short-chain fatty acids were all reduced in rats subjected to bile duct ligation. Mitochondrial protein content per hepatocyte was increased by 32% in rats subjected to bile duct ligation compared with control rats. Thus the studies directly demonstrate mitochondrial defects in fatty acid oxidation in rats subjected to bile duct ligation, which explain decreased ketosis during starvation.

Mechanisms of impaired hepatic fatty acid metabolism in rats with long-term bile duct ligation*1

Mechanisms of impaired hepatic fatty acid metabolism in rats with long-term bile duct ligation*1

Psychosocial stress, catecholamines, and essential fatty acid metabolism in rats.

To examine the effects of psychosocial stress and the "stress hormone," epinephrine, on essential fatty acid metabolism in rats, two studies were conducted. In the first, the effects of four weeks of (i) social isolation and (ii) group housing (control) on liver microsomal delta 6 and delta 5 n-6 desaturase activity were studied in group-reared male normotensive (Wistar Kyoto) and spontaneously hypertensive (SHR) rats (n = 5/group). The second study examined the effects of acute ip epinephrine (0.0, 1.0, 2.0, and 4.0 mg/kg) 6 hr prior to and following an ig dose (4 g/kg) of safflower oil (rich in 18:2n-6, LA) on plasma and liver LA, 20:4n-6 (AA), and LA/AA ratios in adult essential fatty acid deficient Sprague-Dawley rats (n = 6/group). In the first experiment, isolation stress significantly inhibited the activity of delta 6 (P < 0.05) and delta 5 (P < 0.01) desaturase in the normotensive rats and of delta 5 desaturase in the SHR (P < 0.05). In the second study, epinephrine increased plasma and liver LA at doses 1.0 and 2.0 mg/kg in most of the fractions examined, and suppressed AA levels. The response of the LA/AA ratio to epinephrine varied between tissues and among lipid fractions, but increased this ratio at the moderate doses (2.0-4.0 mg/kg) of epinephrine in most cases. These data suggest that psychosocial stressors are capable of inhibiting the rate limiting steps of essential fatty acid metabolism and that this response is more pronounced in the SHR than in the Wistar Kyoto. They also suggest that epinephrine is capable of altering the in vivo metabolism of essential fatty acids in the rat.

Effect of various non-hepatotoxic compounds on urinary and liver taurine levels in rats.

Administration of compounds which alter protein synthesis or sulphur amino acid metabolism in rats results in changes in the excretion of urinary taurine. Treatment with diethylmaleate (DEM) or phorone, which will deplete glutathione (GSH), reduces taurine excretion, whereas treatment with buthionine sulphoximine (BSO), which will inhibit glutathione synthesis, increases taurine excretion. Treatment with cycloheximide, an inhibitor of protein synthesis, increases taurine excretion, whereas pretreatment with phenobarbital, which will increase protein synthesis, decreases taurine excretion. Administration of agents which damage organs other than the liver such as the kidney, heart and testes, does not increase urinary taurine.

Changes in brain ECF amino acids in rats with experimentally induced hyperammonemia.

Using microdialysis, we studied brain extracellular fluid (ECF) amino acid metabolism in rats with experimentally induced hyperammonemia and regional elevation of brain ECF ammonia levels. The total brain ECF amino acid level was increased by an elevation of the blood ammonia level. Hyperammonemia elevated brain ECF aromatic amino acids and reduced arterial blood branched chain amino acids. When rats with hyperammonemia were intravenously administered norleucine, the brain ECF norleucine level rose markedly, suggesting increased permeability of the blood-brain barrier. When rats with hyperammonemia were infused with a branched chain amino acid-rich preparation, the elevated brain ECF aromatic amino acids level was not suppressed. Following local intracerebral ammonia infusion, only glutamate levels showed a marked elevation. These results suggest that impairment of the blood-brain barrier related to hyperammonemia increases the inflow of low molecular weight substances including amino acids. Furthermore, the ammonia-induced increase of glutamate in the cerebral ECF suggests that high ammonia levels may increase the excitability of the brain. Thus, ammonia may serve as a key factor in the onset of hepatic encephalopathy.

Dietary fish oil interferes with renal arachidonic acid metabolism in rats: Correlations with renal physiology

Dietary fish oil has been reported to have both beneficial and deleterious effects in animal models of renal disease, which may be related to alterations in renal eicosanoid metabolism. The influence of dietary fish oil on glomerular and renal tubular responses that are linked to arachidonic acid metabolism was examined. Dietary fish oil had antidiuretic and antinatriuretic effects, which correlated with reduced renal cortical endogenous prostaglandin E 2 (PGE 2). Fish oil altered the renal balance of dienoic prostacyclin (PGI 2) to thromboxane (TXA 2) in favor of vasodilation, which may explain the observed exaggerated compensatory increases in glomerular function in response to uninephrectomy. Intact rats fed fish oil for 6 months developed proteinuria and impaired glomerular filtration rates (GFR). These deleterious effects were associated with evidence of increased renal lipid peroxidation. These results suggest that dietary fish oil modifies glomerular and renal tubular function in rats, and worsens age-associated proteinuria and declines in GFR. These effects may reflect the impact of dietary fish oil on renal fatty acid composition and arachidonic acid metabolism.

Bile Acid Metabolism in Rats Fed Two Levels of Corn Oil and Brans of Oat, Rye and Barley and Sugar Beet Fiber , , ,

High concentrations of fecal bile acids are associated with a higher incidence of colon cancer. Dietary changes that alter bile acid metabolism are therefore of interest. Here, we report the effect of feeding diets containing four fiber sources and two fat levels for 7 wk on bile acid excretion and small intestinal bile acids (an index of pool size) in rats. The fiber sources were oat bran, rye bran, barley bran and sugar beet fiber. Fiber-containing diets were 8% dietary fiber and contained either 5 or 20% corn oil. All fiber sources caused significantly greater fecal output compared with the fiber-free basal diet. All fiber sources also resulted in significantly (P < 0.05) lower fecal bile acid concentration compared with the fiber-free basal diet. Only rye bran resulted in significantly (P < 0.05) higher total fecal bile acid excretion. Oat bran resulted in a slightly but significantly (P < 0.05) higher quantity of small intestine bile acids compared with the other diets. Dietary fat level had no significant effect on fecal bile acid concentration or excretion or quantity of small intestinal bile acids. We conclude that all four fiber sources tested resulted in lower fecal bile acid concentration, by effectively causing greater fecal mass. Changes in dietary fat level as corn oil had no effect on fecal bile acids.

The effect of chemical hepatocarcinogenesis on liver phospholipid composition in rats fed N-6 and N-3 fatty acid-supplemented diets.

The effect of dietary fats on essential fatty acid metabolism in rats subjected to chemically induced hepatocarcinogenesis was studied. Sixty male rats were fed a diet supplemented with one of the following three oil compositions: 10% hydrogenated coconut oil (HCO); 5% hydrogenated coconut oil and 5% gamma-linolenic acid (18:3n-6)-rich evening primrose oil (EPO); or 5% hydrogenated coconut oil and 5% marine oil (FO). Half of the animals in each dietary regimen were subjected to hepatocarcinogenesis induction using diethylnitrosamine and 2-acetylaminofluorene (2-AAF) followed by partial hepatectomy, whereas the other half underwent hepatectomy without receiving diethylnitrosamine and 2-acetylaminofluorene. Liver phospholipid composition was analyzed. In comparison to the HCO group, the EPO group showed raised levels of arachidonic acid (20:4n-6) and suppressed n-3 fatty acids. The FO group, on the other hand, showed suppressed levels of n-6 and increased n-3 fatty acids. Hepatocarcinogenesis suppressed the level of 20:4n-6 and this effect was greater in the FO rats. The levels of dihomo-gamma-linolenic acid (20:3n-6) were increased by the hepatocarcinogenic treatment, and this effect was further accentuated in the EPO rats. These results suggest that hepatocarcinogenesis may suppress the activity of delta-5-desaturase, which may be one of the reasons why tumor cell membranes have low levels of long chain fatty acids, especially 20:4n-6 cells, and have an impaired capacity to undergo lipid peroxidation.

Effect of chitosan feeding on intestinal bile acid metabolism in rats

The effect of chitosan feeding (for 21 days) on intestinal bile acids was studied in male rats. Serum cholesterol levels in rats fed a commercial diet low in cholesterol were decreased by chitosan supplementation. Chitosan inhibited the transformation of cholesterol to coprostanol without causing a qualitative change in fecal excretion of these neutral sterols. Increased fiber consumption did not increase fecal excretion of bile acids, but caused a marked change in fecal bile acid composition. Lithocholic acid increased significantly, deoxycholic acid increased to a lesser extent, whereas hyodeoxycholic acid and the 6 beta-isomer and 5-epimeric 3 alpha-hydroxy-6-keto-cholanoic acid(s) decreased. The pH in the cecum and colon became elevated by chitosan feeding which affected the conversion of primary bile acids to secondary bile acids in the large intestine. In the cecum, chitosan feeding increased the concentration of alpha-,beta-, and omega-muricholic acids, and lithocholic acid. However, the levels of hyodeoxycholic acid and its 6 beta-isomer, of monohydroxy-monoketo-cholanoic acids, and of 3 alpha, 6 xi, 7 xi-trihydroxy-cholanoic acid decreased. The data suggest that chitosan feeding affects the metabolism of intestinal bile acids in rats.

Impaired fatty acid metabolism in rats with secondary biliary cirrhosis

Impaired fatty acid metabolism in rats with secondary biliary cirrhosis

Effects of Corn Oil and Wheat Brans on Bile Acid Metabolism in Rats

High concentrations of colonic bile acids may promote tumor formation. Some studies have found that high levels of dietary fat increase fecal bile acid excretion, whereas others report no effect. Wheat bran appears to reduce fecal bile acid concentration. This study was conducted to determine the effect of different dietary fat levels and types of wheat bran on bile acid metabolism. Rats were fed diets containing either no fiber, 2% cholestyramine (CHO) or brans of hard red spring, soft white winter or durum wheat--at both a 5 or 20% fat level. Animals were fed for 7 wk, and feces were collected in the last week. Wheat bran (all types) significantly increased fecal mass approximately fourfold, and CHO significantly increased fecal mass twofold compared to the fiber-free diet. Increasing the fat level did not increase fecal bile acid excretion, nor did the addition of wheat bran. Addition of CHO, however, more than doubled it. CHO increased fecal bile acid concentration, all wheat brans decreased it and fat level had no effect. Bile acid pool size was increased slightly by fat level and cholestyramine feeding but not by wheat brans. These results indicate that fat level slightly alters bile acid metabolism but that wheat brans do not.

Effect of exogenous cortisone on amino acid metabolism in rats

1. 1. The effect of exogenous cortisone on concentration of free amino acids in serum, skeletal muscle, kidney, small intestine and liver was studied. 2. 2. The amino acid pool in serum, skeletal muscle and small intestine decreased significantly. 3. 3. Glutamine synthesis increased significantly in skeletal muscle. 4. 4. Levels of branched amino acids increased in serum and small intestine. 5. 5. Levels of alanine increased in kidney and liver.

Age–related changes of bile acid metabolism in rats

Cholesterol and bile acid leves were examined in young (8 weeks), middle-aged (12 months) and old (24 months) germ-free male rats, and young (8 weeks) and middle-aged (12 months) conventional male rats. The plasma cholesterol levels were higher in the aged rats, being more marked in the conventional rats. The liver cholesterol levels also increased with age and the increases were almost identical for both groups. No age–related changes were found in the biliary bile acid secretion, the pool size and distribution of bile acids in the bile, small intestine and large intestine, nor in the turnover frequency of bile acids, but the pool size in the young and middle–aged germ–free rats was much larger than that in the conventional rats. The turnover frequency was less in the germ–free rats. The bile acid synthesis presumed from the fecal bile acid excretion decreased in the aged germ–free rats but not in the conventional rats. A most remarkable age–related change was found in the bile acid composition; cholic acid increased and β-muricholic acid derived from chenodeoxycholic acid in the rat decreased by aging, resulting in an increase of the CA/CDCA ratio (bile acids belonging to the cholic acid group/bile acids to the chenodeoxycholic acid group) in the bile, feces and pool. These results suggest that cholic acid synthesis increases while chenodeoxycholic acid synthesis is impaired by aging in rats.

Effect of phosphatidylethanolamine and its constituent base on the metabolism of linoleic acid in rat liver

Dietary phosphatidylethanolamine (PE) contributes the circulatory and hepatic free-ethanolamine in rats (Ikeda et al. (1987) Biochim. Biophys. Acta 921, 245). A role for circulatory ethanolamine has not been defined; however, our recent studies have shown that exogenous ethanolamine influences cholesterol and linoleic acid metabolism in rats (Imaizumi et al. (1983) J. Nutr. 113, 2403). In order to understand the role of dietary PE the effects of PE and its base on the hepatic metabolism of linoleic acid were investigated in vivo and in primary cultured hepatocytes in rats. Dietary PE increased the plasmic level of ethanolamine from 37 to 52 μM and decreased the ratio of arachidonate to linoleate in hepatic phospholipids. Activity of hepaticΔ 6-desaturase decreased in rats given PE and the desaturation of [ 14C]linoleate in the cultured hepatocytes decreased by the addition of ethanolamine. Secretion of [ 14C]linoleate labeled very-low-density lipoprotein from the cultured hepatocytes decreased by the addition of ethanolamine. Dietary PE caused an increased formation of CO 2 from [ 14C]acetate by liver slices, and ethanolamine added to the hepatocytes caused an increased oxidation of [ 14C]linoleate and a suppression of fatty acid synthesis from [ 3H]serine. These results suggest that ethanolamine derived from the dietary PE plays a regulatory role in the linoleate metabolism in the liver.

Effect of aging and dietary restriction on bile acid metabolism in rats.

The aim of the present study was to determine whether increased output of phospholipid in bile during aging may be due to alteration of bile acid composition and stimulated hydrophobic bile acid formation. In female Sprague-Dawley rats we examined the influence of aging and life long dietary restriction (60% of the ad libitum intake) on bile flow, total bile acid secretion, bile acid composition and conjugation pattern, as well as phospholipid output. Rats were cannulated at 3.5, 8-12 and 24-27 months of age and bile collected for analysis. With age, there was a significant reduction in bile flow and total bile acid secretion, however, phospholipid output increased. Restriction of dietary intake exerted a beneficial effect on the age-related decline in bile formation. Studies of bile composition indicated that 12 alpha-hydroxylated bile acids (cholic acid and deoxycholic acid) secretion decreased in aged rats compared to 3.5-month-old rats. This was associated with a corresponding increase in secretion of chenodeoxycholic acid and hyodeoxycholic-ursodeoxycholic acid. However, the magnitude of the change in secretion of these bile acids could not account for the increased output of phospholipid in bile.

Effects of chronic inhibition of glutathione biosynthesis on cholesterol and bile acid metabolism in rats

The objective of this study was to examine the effect of chronic inhibition of glutathione (GSH) biosynthesis on cholesterol and bile acid metabolism in rats. Male Sprague-Dawley rats, weighing between 60 and 65 g, were randomly assigned to one of two groups and allowed a 1-week adaptation period to a 6 a.m.–6 p.m. light cycle. Food and water were available ad libitum. Following the adaptation period, 1 group was given a solution of 30 mM dl-buthionine sulfoximine (BSO, an inhibitor of GSH biosynthesis) in saline, while the other group received saline only. All studies were carried out during, or at the end of the second week of BSO treatment. While body weight was minimally affected by BSO treatment, liver weight (% of body weight) was significantly greater in the BSO group (control 4.8 ± 0.2 vs. BSO 5.2 ± 0.3; P < 0.05). The increase in liver weight, however, was not associated with a change in the specific content of cytochrome P-450. Even though fecal output (g/100 g per day) was significantly greater in the BSO group (control 2.4 ±0.1 vs. BSO 2.7 ± 0.3; P < 0.05), it was not commensurate with an increase in fecal bile acids and neutral sterols. In fact, fecal bile acid excretion (mg/100 g per day) was significantly reduced in the BSO group (control 9.0 ± 2.0 vs. BSO 6.2 ± 0.9; P < 0.05), a finding consistent with a significant reduction in bile acid pool size (mg/100 g) in that group (control 23.1 ± 1.9 vs. BSO 14.3 ± 4.8; P < 0.05). Hepatic GSH content (μmol/g) and cholesterol 7α-hydroxylase activity (pmol/mg per min) were assayed at two time points: 12–2 a.m. (mid-dark point) and 12–2 p.m. (mid-light point). At mid-dark point, BSO-treated animals had a significantly lower hepatic GSH content (control 4.5 ± 0.3 vs. BSO 0.6 ± 0.3; P < 0.05) and a significantly lower cholesterol 7α-hydroxylase activity (control 33.5 ± 1.3 vs. BSO 14.7 ± 3.9; P < 0.05). At mid-light point, hepatic GSH content in the two groups was similar to that at mid-dark point. While cholesterol 7α-hydroxylase activity in both groups was significantly lower ( P < 0.05) at mid-light point relative to that at mid-dark point, there was no difference between the two groups in cholesterol 7α-hydroxylase activity at mid-light point. This suggests that the amplitude of the diurnal rhythm of cholesterol 7α-hydroxylase activity was reduced by chronic inhibition of GSH biosynthesis, resulting in the reduction in bile acid pool size. The results of this study suggest that while hepatic GSH content does have a role in regulating the diurnal rhythm of cholesterol 7α-hydroxylase activity, it is probably not the only factor Involved.

Effects of low magnesium diet on the vascular prostaglandin and fatty acid metabolism in rats

Deficiency of magnesium with cardiovascular effects is thought to be related to alterations in the biosynthesis of prostaglandins (Pgs) in the vasculature. Measurements were made of the PGE2, 6-keto-PGF1α and the thromboxane B2 (TxB2) outflow from the perfused isolated mesenteric arterial bed and the fatty acid composition of the tissue in rats maintaines for 14 weeks on a low magnesium (LMg) diet. The serum Mg leves were significantly decreased and the serum Ca levels were significantly increased in the LMg group as compared to the controls. The arachidonic acid concentration in the triacylglyceride fraction was significantly increased in the LMg group. Long chain polyunsaturates such as 22:4n6 and 22:6n3 were consistently increased in the LMg rats as compared to the controls in both the phospholipid and triglyceride fractions as previously reported in other tissues. The PGE2, 6-keto-PG1α and TxB2 outflows were significantly increased in the LMg group as compared to the controls. This findings suggest that the biosynthesis of eicosanoids, mainly PGI 2, is stimulated in Mg deficiency, and this may provide protection against intracellular Mg depletion and Ca accumulation, so as to counteract to the constricted and hyperactive state of the vasculature in such a condition.

Dietary Linolenic Acid and Longer-Chain n-3 Fatty Acids: Comparison of Effects on Arachidonic Acid Metabolism in Rats

Rats were fed graded amounts of purified 18:3n-3 or fish oil concentrate in the presence of a constant amount of 18:2n-6 to evaluate the ability of 18:3n-3 compared with longer-chain n-3 fatty acids to inhibit 20:4n-6 metabolism in platelets and lungs. Dietary 18:3n-3 at a ratio of 0.28 (n-3 to n-6 fatty acids) suppressed levels of 20:4n-6 in lung and plasma phospholipids and the capacity of the tissues to synthesize cyclooxygenase-derived products in a dose-dependent fashion. At similar ratios of n-3 to n-6 dietary fatty acids, longer-chain n-3 fatty acids, which are abundant in fish oil, appear to be more effective than 18:3n-3 in suppressing 20:4n-6 levels and the capacity of the tissues to synthesize cyclooxygenase-derived products. Much greater amounts of 12-hydroxyeicosapentaenoic acid (12-HEPE) and 5-HEPE than of 12-hydroxyeicosatetraenoic acid (12-HETE) and 5-HETE appeared to be formed in tissues of the group receiving the highest amount of fish oil. These results suggest that ingestion of fish oil leads to increased formation of lipoxygenase-derived products of longer-chain n-3 fatty acids.