Rate Of Protein Secretion Research Articles

Phospholipase A2-catalysed modification of plasma low density lipoproteins caused reduction of hypercholesterolemic rabbit plasma cholesterolin vivo

Phospholipase A2 (PLA2) hydrolyses certain phospholipids of low density lipoproteins. PLA2-treated LDL is known to be rapidly cleared from plasma. A prototype plasma filter containing immobilizedCrotalus atrox PLA2 on agarose beads was developed. After a 90 min treatment with the extracorporeal device, plasma cholesterol concentration in cholesterol-fed NZW rabbits decreased by 32%. The decrease was dependent on the enzymatic activity in the plasma filter. The decrease in plasma cholesterol of hypercholesterolemic rabbits that were treated with control reactors (agarose beads only) was 5%. White and red blood cell counts and platelets remained unchanged during the treatment. Plasma cholesterol reduction (25–40%) was also obtained following intravenous injection of active PLA2 to modify plasma lipoproteins. PLA2 infusion created a radical change in biliary composition. Bile phospholipid composition was 90–95% lysophosphatidylcholine as compared with more than 95% before injection of active PLA2. Phospholipid and bile salts total mass increased by 10%. While biliary secretion rate of protein increased by 10%, biliary secretion rate of cholesterol remained unchanged. This technique is specific for lipoproteins, does not require any fluid replacement of sorbent regeneration, and offers a potential new approach for lowering serum cholesterol and LDL levels.

Morphological Characterization of Immortalized Hypothalamic Neurons Synthesizing Luteinizing Hormone-Releasing Hormone

An immortalized LHRH cell line has recently been developed by genetically targeting these neurons for tumorigenesis. One of the subclones, the GT1-7 cells, was characterized at both the light and electron microscopic levels to study the cellular and subcellular organization of these cells, particularly as they relate to biosynthesis, processing, and secretion. The cells were fixed onto slides 18-36 h after plating. LHRH and GnRH-associated peptide (GAP) immunoreactivities (IR) were detected by immunocytochemistry using colloidal gold labeling. These cultured cells exhibited the classical neuronal appearance of LHRH neurons, and they established numerous interconnections. Neighboring neurons were coupled by tight junctions, while more distant cells were interconnected with neural axon-like processes and collaterals. This cellular organization is suggestive of a neural network where neuronal activity is coordinated. At the ultrastructural level, the nondividing cells possessed indented nuclei, well developed Golgi complexes, and abundant numbers of ribosomes and secretory granules. Clathrin-coated vesicles were found in fusion with the plasma membrane. The ribosomes and secretory vesicles were particularly prominent, suggestive of high rates of protein biosynthesis and secretion. All of the cells immunostained for both LHRH and GAP; however, GAP IR was always more pronounced than that for LHRH. This finding was corroborated by biochemical data reported in a companion paper. The GAP IR was associated with ribosomes and secretory vesicles. By comparison, LHRH IR was restricted mainly to the secretory vesicles. Using colloidal gold particles of different sizes to denote LHRH or GAP IR, it was determined that both GAP and LHRH IR were colocalized within the same secretory vesicle. Taken together, these data suggest that pro-LHRH is biosynthesized on the ribosomes, packaged as an intact protein into the secretory vesicles, processed to LHRH and GAP-(1-56) within these vesicles, and transported to the periphery of the cell in preparation for secretion. These morphological data emphasize the utility of using these immortalized LHRH neuronal cells to dissect the cellular and subcellular architecture involved in biosynthesis, processing, and secretion. In addition, our results provide the first detailed evidence for the intracellular pathway involved in pro-LHRH biosynthesis, processing, and secretion in these cultured neuronal cells.

Studies in human lactation: milk composition and daily secretion rates of macronutrients in the first year of lactation

Time-dependent changes in milk composition and secretion from pregnancy through greater than or equal to 6 mo of exclusive breast-feeding were studied in 13 multiparous women. Concentrations and secretion rates of lipid, lactose, protein, sodium, chloride, potassium, total calcium, ionized calcium, magnesium, glucose, citrate, inorganic phosphate, creatinine, and urea and pH were analyzed longitudinally from day 6 until weaning commenced. The composition of the antepartum secretion was related to the permeability of the junctional complexes between mammary cells. Significant increases in lactose, glucose, pH, and ionized calcium and significant decreases in protein, sodium, potassium, chloride, and calcium concentrations were observed between 1 and 6 mo. Significant differences among individuals, which persisted through lactation, were observed for the concentrations of sodium, potassium, chloride, and inorganic phosphate. The amount of lactose, ionized calcium, and magnesium transferred to the infant was also characteristic of each mother-infant pair. Our data imply that lactation performance is determined in the first month postpartum.

Metabolism of n−3 polyunsaturated fatty acids by the isolated perfused rat liver

The hepatic metabolism of oleic acid and n-3 fatty acids (eicosapentaenoic acid, EPA and docosahexaenoic acid, DHA), and secretion of very low density lipoprotein (VLDL) were studied in isolated perfused rat livers from normal chow fed male rats. The basal perfusion medium contained 30% bovine erythrocytes, 6% bovine serum albumin (BSA), and 100 mg/dL glucose, in Krebs-Henseleit bicarbonate buffer (pH 7.4), which was recycled through the liver for 2 hr. Individual fatty acids (EPA, DHA or oleic acid), as complexes with 6% BSA, or albumin alone, were infused at a rate of 70 mumol/hr. When any of these fatty acids was infused at this rate, the ambient concentration in the medium was maintained at 0.3-0.4 mumol/mL, indicative of similar hepatic rates of uptake for each fatty acid (i.e., approximately 6 mumol/g liver/hr). When fatty acid was not infused, the ambient free fatty acid level was 0.16 mumol/mL. The concentrations of infused free fatty acids increased appropriately in the perfusion medium; however, with infusion of EPA, DHA, or oleate, the concentrations of perfusate palmitate and linoleate were the same as when fatty acid was not infused. Additionally, the perfusate concentration of oleate in the free fatty acid fraction was not affected by infusion of EPA and DHA. These data indicate a constant outflow of endogenous fatty acid unaffected by the presence of the exogenously supplied fatty acid. The net secretion rate of VLDL lipids and protein was stimulated by infusion of oleate, whereas when EPA was infused, secretion rates were lower and similar [except for VLDL cholesterol (C), which was greater] to those occurring when fatty acid was not provided.(ABSTRACT TRUNCATED AT 250 WORDS)

Induction of Hepatocyte Differentiation by the Extracellular Matrix and an RGD-Containing Synthetic Peptide

ABSTRACTTo design novel biomaterials for hepatocyte transplantation it will be necessary to determine whether specific extracellular matrix (ECM) molecule(s) or the adhesive interactions between the surface and hepatocytes are responsible for regulation of hepatocyte function. Purified ECM molecules (laminin, fibronectin, types I and IV collagen) and a synthetic peptide containing the arginine-glycine-aspartate (RGD) cell-binding sequence were precoated at defined densities to non-adhesive polystyrene dishes. Hepatocytes cultured on dishes coated with a low density of ECM molecules (1 ng/cm2) maintained a round morphology, and high liver-specific protein secretion rates. In contrast, culturing hepatocytes on increasing ECM densities (50–1000 ng/cm2) resulted in extensive cell spreading, a loss of liver-specific protein secretion, and cell growth. Hepatocytes cultured on dishes coated with the RGD-containing peptide did not spread even on a high density of the peptide (10,000 ng/cm2), and albumin secretion remained high for hepatocytes cultured on all peptide densities (1–10,000 ng/cm2). These results suggest that a variety of ECM molecules and synthetic peptides are capable of inducing hepatocyte differentiation in vitro, and these effects depend on their ability to promote cell spreading.

Increased hepatic lipase activity and increased direct removal of very-low-density lipoprotein remnants in Watanabe heritable hyperlipidaemic (WHHL) rabbits treated with ethinyl oestradiol

We studied the effects of ethinyl oestradiol on the serum concentrations and metabolism of very-low- and low-density lipoproteins (VLDL and LDL) in Watanabe heritable hyperlipidaemic (WHHL) homozygous rabbits, an animal model for familial hypercholesterolaemia. The results were compared with those in untreated homozygotes as well as in heterozygotes treated or not with ethinyl oestradiol. The gain in body weight was similar in all groups. Treatment with ethinyl oestradiol resulted in the homozygotes in an approx. 80% decrease in the concentrations of lipids and apoprotein B in the d less than 1.019 lipoprotein fraction; those in the LDL fraction did not change. In the heterozygotes, basal serum lipids and apoprotein B levels in the d less than 1.019 fraction were low; ethinyl oestradiol treatment especially affected the LDL fraction (cholesterol -84%, apoprotein B -64%). Turnover experiments with 125I-labelled VLDL revealed that, on treatment with ethinyl oestradiol, the fractional catabolic rate in homozygous rabbits increased 2-fold. The secretion rates of lipids and protein in the d less than 1.019 fraction as estimated after injection of Triton WR-1339 was not decreased. In homozygotes and heterozygotes increases in post-heparin hepatic lipase activity of 62 and 80% respectively were observed, with no changes in lipoprotein lipase activity. We conclude that ethinyl oestradiol induces in homozygous WHHL rabbits a direct removal of VLDL and VLDL remnants from the plasma, apparently due to an increase in hepatic lipase activity.

Interferon-induced transcriptional and post-transcriptional modulation of factor H and C4 binding-protein synthesis in human monocytes

Cultured human monocytes synthesize factor H (H) and C4 binding protein (C4-bp), as assessed by measuring their presence in culture fluids, and demonstrating the presence of their corresponding mRNAs in total monocyte RNA by Northern blot analysis and by nuclear run-on experiments. H mRNA (4.3 kb and 1.8 kb) could only be detected when cycloheximide (2.5 micrograms/ml) was present in monocyte culture fluid. Recombinant interferon-gamma (IFN-gamma) and lymphoblastoid interferon-alpha (IFN-alpha) produce dose-related increases in the synthesis of H and C4-bp and in the abundance of C4-bp mRNA (2.5 kb). Increased abundance of H mRNA was also seen when cycloheximide (2.5 micrograms/ml) was present in the cultures. Both cytokines increased the transcription rates of the H and C4-bp genes. These changes in transcription were rapid, with significant increases being observed within 30 min of exposure. Following the removal of the cytokines from the cultures the transcription rates of both genes returned to control levels within 4 h. The effects of combining IFN-alpha and IFN-gamma on H and C4-bp transcription rates, mRNA abundances and protein secretion rates were not quantitatively additive. The half-life of H mRNA in monocytes was 15 min, whereas that of C4-bp mRNA was 2 h 45 min. Neither half-life was altered by IFN-gamma.

Optimal chemostat cascades for periplasmic protein production.

This theoretical work predicts the optimal system design for the steady-state production of secreted protein in a chemostat cascade, using bakers' yeast (Saccharomyces cerevisiae) as the host organism. The protein of interest, mutant invertase, is secreted to the periplasmic space instead of the culture medium on account of its large size. This work uses the secretion model developed and tested by Park and Ramirez (1988). It is shown that the highest productivity is achieved when the chemostat cascade contains two stages, although the improvement over the single-stage productivity is small. When no recycle is used, the advantage of two stages results from the tradeoff between maximizing the cell concentration and maximizing the rate of protein production per cell. When recycle is used, the cell concentration and protein productivity are increased, and the advantage of two stages results from the tradeoff between maximizing the specific protein production rate and maximizing the specific protein secretion rate. Cascades with three stages were also investigated, but these were found to have no improvement over the corresponding two-stage cascades.

Albumin absorption and protein secretion by the gallbladder in man and in the pig†

To study albumin absorption by the gallbladder in man, an in vitro model was first established in the pig and compared with in vivo function in the same species. Water and electrolyte transport and 125I-albumin absorption and protein secretion in vivo and in vitro were compared. Then similar in vitro studies were performed on human gallbladders obtained at surgery. The in vivo study in the pig was performed without disturbing the gallbladder except to tie a cannula in the cystic duct end. The in vitro model was identical in the pig and human gallbladders. Gallbladders were excised using a technique causing minimal injury and anoxia. They were oxygenated on both mucosal and serosal surfaces in a temperature-controlled environment. Luminal and external bath test solutions consisted of modified Ringers bicarbonate with added glucose; luminal solutions also contained 125I-albumin from different species, depending on the study. Active absorption of sodium and water occurred in both types of studies in the pig but in vivo absorption rates were considerably greater than in vitro rates. Albumin absorption in vivo was substantial; although present in vitro, the absorption of albumin was diminished relatively more than electrolyte transport rates. Protein secretion rates into the gallbladder were similar in vitro and in vivo. The results of studies in the human gallbladders in vitro were similar to the pig, except albumin absorption was greater. Some human gallbladders were obtained from control patients and some from patients with cholesterol gallstones. There were no significant differences between the two groups for any of the variables studied; however, the numbers were small and some control gallbladders were not normal gallbladders.

Effects of Halothane on Human and Rat Hepatocyte Cultures

The aim of this study was to investigate direct cytotoxicity to human and rat hepatocytes in primary culture from halothane and compare it with that of isoflurane, which is known to be minimally metabolized and less toxic in vivo. Both human and rat parenchymal cells were isolated by the two-step collagenase perfusion method and after attachment to plastic were incubated with either volatile anesthetic for 24 h. All the cultures were maintained in 20% O2 condition and were not induced prior to anesthetic treatment. Temperature, atmosphere conditions, and anesthetic concentrations were kept constant during the study period. Evaluation of cytotoxicity was based on morphologic, biologic (determination of both extracellular and intracellular lactate dehydrogenase activity), and metabolic (protein synthesis and secretion) end points. Protein synthesis and secretion rates were found to be the most sensitive parameters in hepatocyte cultures from both species. Protein synthesis was inhibited by 18% and protein secretion by 50% in the presence of 1 and 1.25 mM halothane, respectively, in human cell cultures (P less than 0.05). With 1.25 mM halothane intracellular lactate dehydrogenase was also decreased; lactate dehydrogenase leakage and morphologic alterations were detected only beyond 5 mM halothane. By contrast, in rat hepatocyte cultures protein secretion was inhibited by 26% and protein synthesis by 20% in the presence of 0.1 and 0.75 mM halothane, respectively, whereas morphologic alterations and a 37% lactate dehydrogenase leakage increase were observed with the concentration of 1 mM (P less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Protein secretion by the endometrium during pregnancy in the ewe

Mature Merino ewes were surgically prepared so that after mating they became unilaterally pregnant. Ewes were killed between days 91 and 124 of pregnancy and the uterine milk was collected from the ligated uterine horn. Explants of intercaruncular and intercotyledonary endometrium were collected from the ligated and unligated uterine horns, respectively, and incubated in the presence of L-[4,5-3H]leucine to determine in vitro rates of protein synthesis and secretion. Protein:DNA and DNA:wet tissue ratios were also determined in the explants from some ewes. The proteins secreted in vitro and those present in uterine milk were partially characterized, using several procedures. Antisera raised in rabbits against uterine milk and absorbed against plasma from an ovariectomized ewe were used to detect uterine milk antigens in a variety of tissues and plasma. An average of 150 +/- 26 mL of creamy coloured uterine milk containing 30.7 +/- 4.6 mg mL-1 protein was recovered from 14 ewes. The rates of protein synthesis and secretion in vitro and the protein:DNA ratio were all higher in intercotyledonary than in intercaruncular endometrium, but the predominant radiolabelled protein(s) secreted in vitro by both types of endometrium was shown by gel filtration to have a molecular weight of approximately 60 kDa. This 'uterine pregnancy protein' was not secreted by endometrial explants from a non-pregnant ewe. Uterine milk contained a substantial amount of 60 kDa protein. The molecular weight and lack of sub-unit structure of the 60 kDa fraction of proteins secreted in vitro was confirmed by SDS-acrylamide electrophoresis and density gradient centrifugation. Pronase treatment confirmed the proteinaceous nature of the 60 kDa fraction, and heparin-Sepharose affinity chromatography showed that the predominant secreted protein(s) in this fraction was a glycoprotein. In immuno-double-diffusion tests antisera prepared against uterine milk produced a number of precipitation bands against both uterine milk and culture medium (after incubation of endometrial explants from a pregnant ewe) and a single band against allantoic fluid, but did not react with plasma from an ovariectomized ewe or a day-124 pregnant ewe or its fetus. The antisera did not react with lung, kidney or liver from the same pregnant ewe or with uterine flushings from a non-pregnant ewe. In immuno-electrophoresis tests, at least eight distinct antigens were detected in uterine milk and three of these were also present in allantoic fluid.

Total protein output during rapid reduction of bile salt secretion rates in man.

An investigation was undertaken to study the effect of bile salt secretion on total biliary protein secretion in man. Bile was collected in eight patients from a tube in the bile duct. Collection was started after a meal and continued for six hours, in order to obtain bile salt secretion rates over the entire physiological range. Total protein secretion rates did not vary with change in bile salt secretion or bile flow. The protein pattern assessed by SDS-PAGE did not vary with bile salt secretion. The results indicate that bile salt secretion has little influence on biliary protein secretion under these conditions in man. Changes in bile salt secretion were associated with linear change in bile flow, but there was no relationship between bile flow and protein secretion rates. This argues against convective sieving of plasma proteins into bile.

Neutrophil and eosinophil involvement of the small bowel affected by chronic alcoholism.

Excessive ethanol intake may affect the intestinal mucosa functionally and morphologically. The ethanol effect could partly be the result of inflammatory mechanisms, possibly reflected by an enhanced local granulocyte turnover. This study investigated habitual alcoholics by segmental perfusion of the jejunum and analysed the perfusion fluid content of granulocyte granule constituents. The mean jejunal secretion rate of myeloperoxidase (MPO), a neutrophil granule constituent, was 152 (26) (SE) ng/min/40 cm jejunal segment in the controls (n = 16). The MPO secretion rate in non-cirrhotic habitual alcoholics (n = 7) was on average 450 (103) ng/min and significantly increased compared with controls (p less than 0.001). In contrast alcoholics with cirrhosis (n = 6) had normal MPO secretion rate. The mean secretion rate of eosinophil cationic protein (ECP), an eosinophil granule constituent, was in the controls 77 (15) ng/min/40 cm jejunal segment. Corresponding values in non-cirrhotic and cirrhotic alcoholics were 141 (38) and 130 (93) ng/min, respectively (ns). The data suggest an enhanced neutrophil granulocyte turnover in the jejunum in alcoholics, possibly contributing to the ethanol induced affection of the small bowel. The lack of increased neutrophil activity in cirrhotic alcoholics may reflect a role of the liver for granulocyte activity.

Casein Gene Expression in Bovine Mammary Gland

The objectives were to examine the rate of synthesis of casein mRNA transcripts in bovine mammary tissue at different hormonal states and to study the effects of hormonal stimuli (insulin, hydrocortisone, and prolactin) on the accumulation of casein mRNA and on the rate of protein secretion by epithelial cells from bovine mammary tissues. Total cytoplasmic RNA was extracted from mammary tissues of cows obtained by biopsy (8 mo pregnant) and upon slaughter (lactating). The relative specific activities of cytoplasmic mRNA for αs1-, αs2-, β-, and κ-casein were about 3.2, 4.6, 3.3, and 4.5-fold higher in tissues of lactating cows than in those of 8 mo pregnant cows. Mammary alveolar epithelial cells retained hormone-inducible milk protein gene expression for total milk protein secretion and for αs1- and β-casein messages. Prolactin, even in the absence of insulin and hydrocortisone, induced significant amounts of milk protein mRNA. Hydrocortisone in the presence of prolactin amplified the lactogenic effects on mammary epithelium. Maximal induction of β-casein mRNA and protein secretion occurred when all three hormones were present.

Cryopreservation of isolated rat hepatocytes: A critical evaluation of freezing and thawing conditions

Various parameters, including the nature and proportion of the constituents of the cryoprotective medium, the cooling rate, and the composition of the thawing medium, were evaluated for the cryopreservation of adult rat hepatocytes. The highest percentage of cells able to survive in culture was obtained by freezing in L15 medium containing 16% dimethyl sulfoxide, at a rate of 3 °C/min, and by adding 0.8 M glucose to the thawing medium. More than 50% of hepatocytes capable of attachment just after cell isolation kept this property after freezing and survived in primary culture. Dead cells could be eliminated before seeding by centrifugation on a Percoll layer. In culture, frozen cells exhibited a morphology similar to that of unfrozen cells and after 24 hr their protein secretion rate was reduced by only about 40%.

Tear secretion and lacrimal gland function of rabbits treated with isotretinoin

Adverse ocular reactions including dry eye symptoms and blepharoconjunctivitis are common side effects of treatment with isotretinoin (13- cis-retinoic acid), However, there is little agreement in the literature on the effect of this drug on the tears. Because we have previously shown that the lacrimal gland secretes isotretinoin, we conducted a study of the effect of isotretinoin on lacrimal gland function, Rabbits were treated with isotretinoin for 5 months. Throughout the study tear secretion was monitored by the Schirmer test. At the end of the study lacrimal gland function was assessed by measurement of fluid and protein secretion rates and secretion of retinol in response to a pilocarpine stimulus. Lacrimal gland function was not affected by isotretinoin as compared with a group of age-matched control rabbits; however, Schirmer test scores were signiricantly increased in the treated animals as compared with control values. We conclude that isotretinoin is not toxic to the lacrimal gland of rabbits. This suggests that ocular irritation in patients treated with isotretinoin is not caused by decreased tear secretion during therapy.

Salivary changes associated with experimental motion sickness condition in man

The effect of experimental motion sickness condition (rotation) on salivary flow and composition was studied in 34 healthy male volunteers. In most subjects, the flow rate of whole saliva was significantly decreased, while the potassium concentration was markedly increased during rotation. These results contrast with the classic reports of subjectively increased salivation in the first stages of motion sickness and may tentatively be explained in terms of sympathetic activation. The salivary protein concentration and secretion rate observed before and during rotation were consistently higher in those subjects categorized as moderately or severely sick during rotation. The salivary protein levels may perhaps be considered as an additional objective variable in the prediction of susceptibility to motion sickness.

Synthesis and secretion of lipoproteins by human hepatocytes in culture.

Confluent monolayers of normal human hepatocytes obtained by collagenase perfusion of liver fragments were incubated in a serum-free medium. Intracellular apolipoproteins apo AI, apo C, apo B, and apo E were detected between Day 1 and Day 6 of the culture by immunoenzymatic staining using polyclonal antibodies directed against these apoproteins and monoclonal antibodies directed against both forms of apo B (B100 and B48). Translation of mRNA isolated from these hepatocytes in an acellular system revealed that apo AI and apo E were synthesized as the precursor forms of mature plasma apo AI and apo E. Three lipoprotein fractions corresponding to the density of very low density lipoprotein (VLDL), low density lipoprotein (LDL), and high density lipoprotein (HDL) were isolated from the medium at Day 5 of culture and examined by electron microscopy after negative staining. VLDL and LDL particles are similar in size and shape to plasma lipoproteins; spherical HDL are larger than normal plasma particles isolated at the same density. Their protein represented 44, 19.5, and 36.5% respectively, of the total lipoprotein protein. The secretion rate of VLDL protein corresponded to that measured in primary cultures of rat hepatocytes. After incorporation of [3H]glycerol, more than 92% of the [3H]triglyceride secreted into the medium was recovered in the VLDL fraction. These results demonstrate that primary cultures of normal human hepatocytes are able to synthesize and secrete lipoproteins and thus could be a useful model to study lipoprotein metabolism in human liver.

Role of acetaldehyde in the ethanol-induced impairment of hepatic glycoprotein secretion in the rat in vivo.

Ethanol administration inhibits hepatic protein and glycoprotein secretion. Previous studies have shown that the metabolism of ethanol is required for this effect. Experiments were designed to determine whether acetaldehyde, the first metabolite of ethanol oxidation, mediated the ethanol-induced secretory defect in rats with normal and stimulated (inflammation-induced) rates of hepatic protein secretion. This study used cyanamide, an aldehyde dehydrogenase inhibitor, to correlate enhanced acetaldehyde levels with an increased ethanol-induced inhibition of hepatic protein secretion. Inflammation was induced by turpentine 24 hr prior to cyanamide (5 mg per kg body weight) or saline pretreatment. Nonfasted rats were intragastrically gavaged with ethanol (4 to 6 gm per kg body weight) or isocaloric glucose 1 hr following pretreatment. [3H]Fucose and/or [14C]leucine were injected intravenously 2 hr following intubation. With elevated levels of acetaldehyde, the ethanol-induced impairment of secretion of labeled proteins and their parallel retention in the liver were markedly potentiated. During inflammation, this inhibition of secretion by ethanol was maintained and further increased with cyanamide pretreatment. These results indicate that the ethanol-induced impairment of hepatic glycoprotein secretion is mediated by acetaldehyde in both normal and inflammation-stimulated animals.

Effect of a Low Protein Diet on Bile Flow and Composition in Rats

The effect of feeding a low protein (LP) diet on bile flow and biliary lipid and protein secretion was studied with young female rats. Animals fed a 8% protein diet (LP) for 4, 8 and 12 wk had a significantly lower bile flow and a lower biliary bile acid and protein secretion rate compared with rats fed a 26% protein (normal) diet (NP). The bile acid-independent fraction of bile flow was significantly increased. The slope of the regression line to zero bile acid was markedly smaller in the LP than in the NP group, indicating lower bile acid-dependent bile flow. Biliary phospholipid and cholesterol secretion rates were significantly higher in the LP than in the NP group, demonstrating an uncoupling between bile acid and lipid secretion at the low rates of bile acid secretion. The percentage increase for these parameters was of similar magnitude (30%). Absolute concentrations of bile acid, phospholipid and cholesterol were significantly higher in LP-fed rats than in NP rats, while relative concentration of bile acid was lower and those of cholesterol and phospholipid were higher. Analysis of biliary bile acids showed that the percent contribution of chenodeoxycholic acid and of deoxycholic acid increased significantly in the LP-fed rats, while that of cholic acid decreased. These data indicate that the lower bile flow in the rats fed LP can be attributed to lower bile salt-dependent flow associated with significantly lower choleretic potency of bile acids secreted.