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Biomedical subjects

W Stremmel

Publications and source records attributed to W Stremmel.

At least 253 records · Page 14Linked to original sources
PubMed1987

Translocation of fatty acids across the basolateral rat liver plasma membrane is driven by an active potential-sensitive sodium-dependent transport system.

In previous studies it was shown that hepatocellular uptake of fatty acids is mediated by a specific fatty acid binding membrane protein. To determine now directly the driving forces for their entry into hepatocytes, the uptake of a representative long chain fatty acid, [3H]oleate, by basolateral rat liver plasma membrane vesicles was examined. Influx of oleate was stimulated by increasing the Na+ concentration of the medium. In the presence of an inwardly directed Na+ gradient (NaSCN, NaNO3, NaCl) oleate was accumulated during the initial uptake phase (20 s) at a concentration of 1.4-1.9-fold that at equilibrium (overshoot). This activation of influx was not observed after replacement of Na+ by Li+, K+, or choline+. Na+-dependent oleate uptake was significantly stimulated by creation of a negative intravesicular potential, either by altering the accompanying anions or by valinomycin-induced K+ diffusion potentials, suggesting an electrogenic transport mechanism. Na+-dependent fatty acid uptake was temperature dependent, with maximal overshoots occurring at 37 degrees C, and revealed saturation kinetics with a Km of 83.1 nM and Vmax of 2.9 nmol X min-1 X mg protein-1. These studies demonstrate that the carrier-mediated hepatocellular uptake of fatty acids represents an active potential-sensitive Na+-fatty acid cotransport system.

Action Potentials↗
PubMed1987

Haemochromatosis.

Explore the source record for details and available documents.

Diabetes Mellitus↗
PubMed1987

Enhanced biliary gamma-glutamyltransferase excretion following prolonged alcohol consumption in rats.

In order to study the question of whether chronic ethanol consumption may alter the biliary excretion of gamma-glutamyltransferase (gamma-GT), female rats were pair-fed nutritionally adequate liquid diets containing either ethanol (36% of total calories) or isocaloric carbohydrates for 24 days. Compared to pair-fed controls, the administration of the alcohol-containing diet resulted in an increased biliary excretion of gamma-GT (5.84 +/- 0.73 mU 6 h-1 100 g-1 b.w. vs. 8.82 +/- 0.79, P less than 0.001). This was associated with a corresponding enhanced biliary output of total bile acids. An apparent linear relation between the biliary output rates of gamma-GT and those of total bile acids was observed both in alcohol-fed animals (r = 0.83) and in their pair-fed controls (r = 0.95). In addition, there was a significant increase of gamma-glutamyltransferase activities in the liver homogenate and in liver plasma membranes, both in fractions rich in bile canalicular and basolateral membranes and in those rich in blood sinusoidal site. Serum gamma-glutamyltransferase activities as well as serum bile acid concentrations were also enhanced by 96.8% (P less than 0.001) and 233% (P less than 0.001), respectively. These data show that chronic alcohol consumption enhances hepatic gamma-GT activities, leading to an increased efflux of gamma-GT into the bile and possibly into the blood out of the liver cell. Furthermore, these data suggest the involvement of bile acids with their solubilizing properties for the biliary excretion of gamma-GT.

Alcoholism↗
PubMed1987

Iron uptake by rat duodenal microvillous membrane vesicles: evidence for a carrier mediated transport system.

The mechanism of iron translocation from intestinal lumen to portal plasma is poorly understood. To examine these processes, uptake of Fe2+ and Fe3+ by rat duodenal microvillous membrane vesicles prepared by a Ca2+ precipitation procedure was studied. Membrane aliquots were incubated with increasing concentrations of 59FeCl3 in the presence of a one-thousand-fold molar excess of citrate or 59FeSO4 with a twenty-fold molar excess of L-ascorbic acid. After various time intervals the incubation reaction was stopped by addition of 0.1 mM FeCl3 (4 degrees C), and uptake of 59Fe was determined by a vacuum filtration assay. Initial uptake velocity of 59FeCl3 and 59FeSO4 was determined from the slope of the cumulative uptake curves, which was linear for the first 60 s. Initial uptake rates of both, 59Fe3+ and 59Fe2+ revealed an identical saturable uptake component with a Km of 19-22 nM and Vmax of 8 pmol min-1 mg protein-1. In addition, transport of Fe2+ revealed a linear unspecific uptake phase, which was predominant at high substrate concentrations. Saturable uptake of Fe2+ and Fe3+ was temperature dependent, and significantly reduced by trypsin pretreatment of the microvillous membrane vesicles, indicating the involvement of a protein in the uptake process. This suggestion was pursued by isolation of an iron binding protein from duodenal brushborder membranes. After solubilization of microvillous plasma membranes with 1% Triton X 100, affinity chromatography of the membrane protein mixture over an iron chelate gel derived from epoxy activated Sepharose and elution with 50 mM EDTA yielded a single 52,000 dalton protein. The protein co-chromatographed over an Ultro-Pac TSK G 3000SW HPLC column together with 59FeCl3 and 59FeSO4. It showed no immunologic activity to rabbit antibodies against whole rat serum or rat transferrin. Furthermore, by photoaffinity labelling technique a single iron binding protein with a molecular weight of about 52,000 dalton was identified in microvillous membranes of the rat duodenum. These data are compatible with the hypothesis that intestinal iron absorption is mediated by a specific carrier-dependent transport system.

Animals↗
PubMed1986

Selective inhibition of long-chain fatty acid uptake in short-term cultured rat hepatocytes by an antibody to the rat liver plasma membrane fatty acid-binding protein.

Uptake of long-chain fatty acids by short-term cultured hepatocytes was studied. Rat hepatocytes, which were cultured for 16 h on plastic dishes (3.6 X 10(6) cells/dish), were incubated with [3H]oleate in the presence of various concentrations of bovine serum albumin as a function of the concentration of unbound [3H]oleate in the medium. At 37 degrees C initial uptake velocity (V0) was saturable (Km = 9 X 10(-8) M; Vmax = 835 pmol/min per mg protein). V0 was temperature dependent with an optimum at 37 degrees C and markedly reduced at 4 degrees C and 70 degrees C. To evaluate the biologic significance of a previously isolated rat liver plasma membrane fatty acid-binding protein as putative carrier protein in the hepatocellular uptake of fatty acids, cultured hepatocytes were treated with a monospecific rabbit antibody (IgG-fraction) to this membrane protein or the IgG-fraction of the pre-immune serum as controls. Uptake kinetics of [3H]oleate in antibody pretreated short-term cultured hepatocytes revealed a depression of Vmax by 70%, while Km was only reduced by 16% compared to controls, indicating a predominant non-competitive type of inhibition. V0 of a variety of long-chain fatty acids (oleic acid, arachidonic acid, palmitic acid, stearic acid) was reduced by 56-69%, while V0 of [35S]sulfobromophthalein, [3H]cholic acid and [14C]taurocholic acid remained unaltered. These data support the concept that in the system of cultured hepatocytes, uptake of long-chain fatty acids is mediated by the rat liver plasma membrane fatty acid-binding protein.

Animals↗
PubMed1986

Hepatocellular influx of [14C]oleate reflects membrane transport rather than intracellular metabolism or binding.

When [14C]oleate bound to bovine serum albumin was incubated at 37 degrees C for 7 min with isolated rat hepatocytes in the absence of glucose, the cumulative oleate uptake curve had two components: a rapid, linear segment over the first 30 sec, followed by a slower, curvilinear component. At 173 microM [14C]oleate/albumin (1:1, mol/mol), the initial component had a slope (Vo) of 118 +/- 18 pmol per min per 5 X 10(4) hepatocytes (mean +/- SD). During this initial 30 sec, virtually no oleate was oxidized, and less than 11% was esterified. By 5 min, 79% was esterified; oxidation never exceeded 4%. Addition of 2 mM glucose significantly increased oleate esterification and thereby available oleate binding sites on cytosolic fatty acid binding protein but had no influence on Vo. Pretreatment with trypsin reduced Vo by 49 +/- 15%. These data indicate that the initial component of the oleate uptake curve reflects predominantly influx, whereas the subsequent component reflects a balance between influx, efflux, and intracellular metabolism. Influx is independent of intracellular binding, oxidation, and esterification and may reflect a membrane-associated carrier-mediated process.

Animals↗
PubMed1986

Hepatocellular uptake of oleate is energy dependent, sodium linked, and inhibited by an antibody to a hepatocyte plasma membrane fatty acid binding protein.

Several studies suggest that a portion of hepatocellular nonesterified fatty acid uptake may be carrier mediated. To further investigate this process, initial rates (Vo) of [14C]oleate uptake into rat hepatocytes, isolated by collagenase perfusion and incubated at 37 degrees C with oleate in the presence of bovine serum albumin, were studied as a function of the concentration of unbound [14C]oleate in the medium. Vo was saturable with increasing unbound oleate concentration (Km = 8.3 X 10(-8) M; Vmax = 197 pmol per min per 5 X 10(4) hepatocytes) and was not inhibited by up to 40 microM sulfobromophthalein, taurocholate, or cholic acid. Oleate uptake was sodium dependent. Vo was significantly diminished when Li+, K+, choline, or sucrose were substituted for Na+ in the incubation medium and was reduced 46% by 1 mM ouabain. Uptake was also markedly reduced after exposure of cells to metabolic inhibitors (e.g., 2,4-dinitrophenol, carbonyl cyanide m-chlorophenylhydrazone, antimycin, KCN). To evaluate the physiologic significance of the previously isolated rat liver plasma membrane fatty acid-binding protein, the effect of an antibody directed against this protein on hepatocellular [14C]oleate uptake was examined. Preincubation of hepatocytes with the IgG fraction of this antiserum inhibited Vo of [14C]oleate by up to 65% in dose-related fashion, without altering Vo for [35S]sulfobromophthalein, [14C]taurocholate, or [3H]cholate. These data indicate that at least a portion of hepatocellular oleate uptake is energy dependent, sodium linked, and mediated by a specific liver plasma membrane-fatty acid-binding protein.

Animals↗
PubMed1986

Hepatocellular uptake of sulfobromophthalein and bilirubin is selectively inhibited by an antibody to the liver plasma membrane sulfobromophthalein/bilirubin binding protein.

To clarify sulfobromophthalein (BSP) and bilirubin uptake mechanisms, isolated rat hepatocytes were incubated with [35S]BSP. The initial uptake velocity (V0), determined from the first, linear portion of the cumulative uptake curve, was saturable (Michaelis constant [Km] = 6.2 +/- 0.5 microM; Vmax = 638 +/- 33 pmol X min-1 per 10(5) hepatocytes), maximal at 37 degrees C and pH 7.4, and competitively inhibited by bilirubin, but not by taurocholate, cholate, or oleate. Preloading with unlabeled BSP led to trans-stimulation of V0. Sodium substitution or pretreatment of hepatocytes with ouabain or metabolic inhibitors had no effect on V0; trypsin reduced V0 by 39% (P less than 0.001). A rabbit antiserum to the rat liver plasma membrane (LPM)-BSP/bilirubin binding protein selectively reduced V0 of 5 microM [35S]BSP and [14C]bilirubin by 41 and 42%, respectively (P less than 0.01); uptakes of [3H]oleate, [3H]cholate and [3H]taurocholate were not affected. Hence, the LPM-BSP/bilirubin binding protein plays a role in the carrier-mediated uptake of BSP and bilirubin by hepatocytes.

Animals↗
PubMed1985

Survival and causes of death in cirrhotic and in noncirrhotic patients with primary hemochromatosis.

We analyzed survival and causes of death among 163 patients with primary hemochromatosis diagnosed between 1959 and 1983. The mean follow-up period was 10.5 +/- 5.6 years (+/- S.D.). Cumulative survival was 92 per cent at 5 years, 76 per cent at 10 years, 59 per cent at 15 years, and 49 per cent at 20 years. Life expectancy was reduced in patients with cirrhosis of the liver as compared with those without cirrhosis (P less than or equal to 0.05), in patients with diabetes mellitus as compared with those without diabetes (P less than or equal to 0.002), and in patients who could not be depleted of iron during the first 18 months of venesection therapy as compared with those who could be depleted (P less than or equal to 0.001). Prognosis was not influenced by sex (P less than or equal to 0.5). Patients without cirrhosis had a life expectancy that was not different from that expected in an age- and sex-matched normal population. Analysis of the causes of death in 53 patients, as compared with the normal population, showed that liver cancer was 219 times more frequent among the patients (16 patients), cardiomyopathy was 306 times more frequent (3 patients), liver cirrhosis was 13 times more frequent (10 patients), and diabetes mellitus was 7 times more frequent (3 patients). Death rates for other causes, including extrahepatic carcinomas (seven patients), were not different from the rates expected. We conclude that patients with hemochromatosis diagnosed in the precirrhotic stage and treated by venesection have a normal life expectancy, whereas cirrhotic patients have a shortened life expectancy and a high risk of liver cancer even when complete iron depletion has been achieved.

Adolescent↗
PubMed1985

Isolation and partial characterization of a fatty acid binding protein in rat liver plasma membranes.

When [14C]oleate-bovine serum albumin complexes were incubated in vitro with rat liver plasma membranes (LPM), specific, saturable binding of oleate to the membranes was observed. Maximal heat-sensitive (i.e., specific) binding was 3.2 nmol/mg of membrane protein. Oleate-agarose affinity chromatography of Triton X-100-solubilized LPM was used to isolate a single 40-kDa protein with high affinity for oleate. On gel filtration, the protein comigrated with various fatty acids but not with [14C]bilirubin, [35S]sulfobromophthalein, [14C]taurocholate, [14C]phosphatidylcholine, or [14C]cholesteryloleate. A rabbit antibody to this membrane fatty acid-binding protein gave a single precipitin line with the antigen but no reactivity with concentrated cytosolic proteins, LPM bilirubin/sulfobromophthalein-binding protein, or rat albumin or other rat plasma proteins. The antibody selectively inhibited heat-sensitive binding of [14C]oleate to LPM. Immunofluorescence studies localized the antigen in liver-cell plasma membranes as well as in other major sites of fatty acid transport. These data are compatible with the hypothesis that this protein may act as a receptor in a hepatocellular uptake mechanism for fatty acids.

Animals↗
PubMed1985

Pressure studies of the ileocecal sphincter after small bowel resection in rabbits.

The function of the ileocecal sphincter (ICS) in rabbits was investigated after extensive small bowel resection. The reflux pressure in anterograde (P1) and retrograde (P2) direction was measured before, 7 days after, and 1 year after small bowel resection, nd compared with a group of rabbits in which a bypass-operation of the same length of the small bowel had been performed. After 7 days, both P1 and P2 showed a marked decrease in the resection group. One year after the operation, pressures had increased again but were still lower than before the resection. Significantly minor pressure changes were found 7 days after bypass surgery. We consider that ICS-insufficiency can be one cause of the features of short bowel syndrome.

Animals↗
PubMed1985

Identification, isolation, and partial characterization of a fatty acid binding protein from rat jejunal microvillous membranes.

The mechanisms by which FFA are absorbed by the gut are unclear. To examine these processes, binding of [14C]oleate to isolated rat jejunal microvillous membranes (MVM) was studied in vitro. When [14C]oleate alone or compounded with bovine serum albumin at various molar ratios was incubated with MVM aliquots, binding was time- and temperature-dependent, inhibitable by addition of excess cold oleate, and decreased by heat denaturation or trypsin digestion of the membranes. When [14C]oleate binding to heat denatured MVM, which increased continuously as a function of the free oleate concentration and was taken as a measure of nonspecific binding, was subtracted from total binding to native MVM, a curve suggestive of saturable specific binding was observed. In contrast to fatty acids, there was no specific binding of [14C]taurocholate or [35S]sulfobromophthalein to jejunal MVM. After MVM solubilization with 1% Triton X-100, affinity chromatography over oleate-agarose and elution with 7 M urea yielded a single 40,000-mol-wt protein. This Sudan Black/periodic acid-Schiff-stain-negative protein co-chromatographed on Sephadex G-100 with [14C]oleate, [14C]palmitate, [14C]arachidonate, and [14C]linoleate, but not with the [14C]oleate ester of cholesterol, [14C]phosphatidylcholine, [14C]taurocholate, or [35S]sulfobromophthalein. A rabbit antibody to the previously reported hepatic membrane fatty acid binding protein (FABP) gave a single line of immunologic identity between the FABPs of rat jejunum and rat liver membrane. It inhibited the binding of [14C]oleate to native MVM but not heat denatured MVM, and, in immunohistochemical studies, demonstrated the presence of the FABP in the apical and lateral portions of the brush border cells of the jejunum, but not on the luminal surface of esophagus or colon. These data are compatible with the hypothesis that a specific FABP plays a role in fatty acid absorption from the gut.

Animals↗
PubMed1985

Conversion of androgens to estrogens in idiopathic hemochromatosis: comparison with alcoholic liver cirrhosis.

Hypogonadism is common in patients with some liver diseases, such as idiopathic hemochromatosis (IHC) and alcoholic cirrhosis (AC). However, gynecomastia, a typical feature in AC, does not occur in IHC. To determine the hormonal basis for this difference, the following parameters were determined in patients with IHC and AC as well as in normal men: plasma concentrations of androgens and estrogens, metabolic clearance and production rates of androstenedione and testosterone, and the contribution of peripheral conversion of androstenedione and testosterone to the circulating estrogens. Severe impotence in both patients with IHC and those with AC was associated with more than 50% reduction in plasma testosterone. The reduction was due to 63% and 70% decreases in testosterone production in IHC and AC, respectively. The MCRs were less affected in IHC and AC (19% and 37% reductions, respectively). In IHC, the fall in testosterone concentrations was accompanied by decreased production and plasma concentrations of androstenedione, a precursor for estrogen synthesis. In contrast, production and plasma concentrations of androstenedione were significantly increased in AC. Patients with IHC had estradiol und estrone levels similar to those in normal men (mean +/- SD, 16.2 +/- 4.6 vs. 20.3 +/- 3.7 pg/ml; P = NS), whereas in AC, estradiol and estrone were significantly elevated (38.0 +/- 5.3 and 68.5 +/- 17.2 pg/ml, respectively). In IHC, sex hormone-binding globulin levels were in the same range as in the normal men, whereas sex hormone-binding globulin was increased in AC. In IHC, the instantaneous contribution of plasma androstenedione to estrone and estradiol was normal, whereas that of plasma testosterone to plasma estrogens was decreased by about 50%. In contrast, in AC, the instantaneous contribution of plasma androstenedione to estrogens was greatly enhanced, and that of testosterone was in the normal range. Since the MCRs of androgens and the conversion ratios of androgens to estrogens indicate normal peripheral metabolism of sex hormones in IHC, decreased androgen formation implies decreased testicular synthesis. This was confirmed by a significantly decreased LH level in IHC (5.5 +/- 1.9 vs. 10.5 +/- 3.1 mU/ml in normal men), indicating pituitary failure. In AC, however, increased LH (20.0 +/- 2.7 mU/ml) may be indicative of primary testicular failure. These results confirm clinical features of hypogonadism and normal estrogenic activity in patients with IHC.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗