Biomedical subjects

T Berg

Publications and source records attributed to T Berg.

At least 235 records · Page 13Linked to original sources

PubMed1988

Transfer of retinol from parenchymal to stellate cells in liver is mediated by retinol-binding protein.

Newly absorbed chylomicron remnant retinyl ester is endocytosed by parenchymal liver cells, and retinol is subsequently transferred to perisinusoidal stellate cells in liver. In the present study we have used several approaches to elucidate the mechanism for the paracrine transfer of retinol between liver parenchymal and stellate cells. In one series of experiments, chylomicrons labeled with [3H]retinyl palmitate or with retinyl [3H]palmitate were injected intravenously into rats. It was shown that the retinol as well as the palmitate moiety were initially taken up in parenchymal liver cells. However, only the retinol moiety was detected in stellate cells, indicating that the retinyl ester is hydrolyzed before retinol is transferred to stellate cells. It is well known that parenchymal liver cells secrete retinol bound to retinol-binding protein (RBP), and we have recently found that stellate cells do have RBP receptors. Here we report that antibodies against RBP completely block the transfer of retinol from parenchymal to stellate cells. These findings indicate that following uptake of chylomicron remnant retinyl ester in parenchymal cells, the retinyl ester is hydrolyzed, and retinol secreted from parenchymal cells on RBP is taken up by stellate cells by means of RBP receptors.

Animals↗

PubMed1988

Distribution of retinol in rat liver cells: effect of age, sex and nutritional status.

1. We have recently shown that the stellate cells, under normal conditions, contain a majority (more than 80%) of the total store of retinol in liver (Blomhoff et al. 1985). 2. In the present work we have studied the role of the various liver cells in rats of different ages, sex and vitamin A status. 3. In most of these groups of rats, storage of retinol in parenchymal cells was proportional to the liver store of retinol, and less than 10% of total retinol in the liver could be recovered in the parenchymal cells. The only exception was parenchymal cells isolated from vitamin A-deficient rats. In rats containing 5 nmol retinol/g liver, about 16% of total retinol could be recovered in parenchymal cells, while in rats with only 1 nmol retinol/g liver, about 40% of total retinol could be recovered in parenchymal cells. 4. These results indicate that parenchymal cells played a minor role in liver storage of retinol, and that stellate cells stored more than 90% of liver retinol in most instances. Only in rats with a low retinol status did the percentage of retinol in parenchymal cells increase.

Aging↗

PubMed1988

Changes in hepatic parenchymal and nonparenchymal cell vitamin A content during vitamin A depletion in the rat.

Levels of total, unesterified and esterified retinol were determined in liver, liver parenchymal cells (PC) and liver nonparenchymal cells (NPC) during vitamin A depletion in rats. Liver vitamin A levels decreased from 113 to 4 micrograms over a 97-d experimental period; plasma retinol concentrations did not change significantly during this time. Initially, greater than 90% of hepatic vitamin A was in the esterified form and most (93%) was localized in NPC. During vitamin A depletion, there were significant declines in retinyl ester content of both PC and NPC, but unesterified retinol levels were not significantly affected. Plasma retinol concentrations were significantly correlated with unesterified retinol mass in PC and NPC, but not with retinyl ester mass. Although 94% of the liver's negative vitamin A balance was due to changes in NPC retinyl ester levels, the fractional rate of retinyl ester loss from PC and NPC was almost identical. Since unesterified retinol levels in plasma, PC and NPC appeared to be conserved even when liver retinyl ester stores were virtually depleted, and since the retinol utilization rate was apparently not decreasing during this stage of vitamin A depletion, these data support the hypotheses that homeostatic mechanisms controlling the three pools of unesterified retinol are linked, and that vitamin A utilization rate is maintained as long as unesterified retinol levels in plasma, PC and NPC are normal.

Animals↗

PubMed1988

Bacterial agglutinins in rat salivary glands: effect of glandular stimulation and calcium dependency.

The secretory pattern of salivary, bacterial agglutinins was studied in the rat. The three major salivary glands were cannulated bilaterally and their secretions collected separately after parasympathomimetic and sympathetic stimulation. The bacterial aggregating activity of the secretions was tested against four strains of bacteria indigenous to the rat. Agglutinin activity was demonstrated in both parasympathomimetic and sympathetic secretions. The parotid glands tended to show the highest total output of agglutinins, with the highest titers found in parotid saliva on sympathetic stimulation. In submandibular and, particularly, parotid saliva, titers tended to increase when stimulation with pilocarpine was followed by sympathetic stimulation. In contrast, titer in sublingual saliva tended to decrease on sympathetic stimulation. When expressed as titer output per minute, sympathetic parotid secretion showed the highest agglutinin activity. Agglutinin activity appeared unrelated to total protein or to duct-derived amidolytic activity. Titers of parotid or submandibular saliva were increased 5- to 10-fold by the presence of 3.3 mM CaCl2 in the reaction mixture. By contrast, the agglutinating activity of sublingual saliva on parasympathomimetic stimulation was unaffected by extraneous CaCl2. Measurements of Ca concentration in similarly obtained rat salivary secretions did not show patterns of Ca concentration that could be related to the varying sensitivity of the agglutinating activity to Ca.

Agglutinins↗

PubMed1988

Elimination kinetics of circulating antigens and immune complexes. II. Hepatic and extrahepatic elimination of chemically modified albumin preparations in relation to their non-specific physicochemical properties.

Formaldehyde-treated human serum albumin (fHSA) was analysed and compared with dinitrophenylated human serum albumin (DNP35HSA) with respect to net charge, hydrophobicity, and state of aggregation. The blood clearance and tissue distribution of intravenously injected fHSA was studied in mice. Similarly to DNP-HSA, fHSA was rapidly cleared from the blood stream owing to hepatic uptake and to extrahepatic deposition. We found no evidence supporting that fHSA was eliminated from the blood by hydrophobic interaction with cell or tissue surfaces. The blood clearance rate and the hepatic uptake of fHSA was not influenced by the presence of formylated peptides, indicating that receptors for formylated peptides were not involved in the handling of circulating fHSA.

Animals↗

PubMed1987

Liver takes up retinol-binding protein from plasma.

Retinol is transported in plasma bound to a specific transport protein, retinol-binding protein. We prepared 125I-tyramine cellobiose-labeled rat retinol-binding protein and studied its tissue uptake 1, 5, and 24 h after intravenous injection into rats. The liver was the organ containing most radioactivity at all time points studied. After 5 and 24 h, 30 and 22% of the injected dose were recovered in liver, respectively. After separating the liver into parenchymal and nonparenchymal cells in the 5-h group, we found that both cell fractions contained approximately the same amount of radioactivity (per gram of liver). Most of the retinol-binding protein radioactivity in the nonparenchymal cell fraction was in the stellate cells. The implication of these results for a possible transfer mechanism for retinol between parenchymal and stellate cells is discussed.

Animals↗

PubMed1987

Intracellular transport and degradation of chylomicron remnants in rat liver cells after in vivo endocytosis.

The intracellular transport and degradation of in vivo endocytosed chylomicron remnants labelled with 125I in the protein moiety was studied in rat liver cells by means of subcellular fractionation in Nycodenz and sucrose density gradients. Initially, the radioactivity was located in low-density endosomes and was sequentially transferred to light and dense lysosomes. Data from gel filtration of the light and dense lysosomal fractions showed radioactive material with a molecular weight of about 1000-2000, representing short peptide fragments or amino acids which remain attached to iodinated tyramine cellobiose. In addition, undegraded apoproteins accumulated in both types of lysosome. Our data suggest that endocytosed chylomicron remnant apoproteins are first located in low-density endosomes and are sequentially transferred to light and dense lysosomes. Furthermore, the degradation process starts in the light lysosomes.

Animals↗

PubMed1987

The relationship between autophagy and the intracellular degradation of asialoglycoproteins in cultured rat hepatocytes.

The relationship between autophagy and the intracellular distribution of endocytosed asialoorosomucoid was studied in cultured rat hepatocytes. Overt autophagy was induced by shifting the cells to a minimal salt medium. Incubation in minimal salt medium led to the formation of buoyant lysosomes at the expense of denser lysosomes manifested as a dual distribution of these organelles in Nycodenz gradients. Asialoorosomucoid was labeled with 125I-tyramine cellobiose. The labeled degradation products formed from this ligand are trapped at the site of degradation and may therefore serve as markers for the subgroup of lysosomes involved in the degradation. In control cells the degradation of the ligand was initiated in a light prelysosomal compartment and continued in denser lysosomes. In cells with high autophagic activity, the degradation of labeled asialoorosomucoid took place exclusively in a buoyant group of lysosomes. These results suggest that degradation of endocytosed ligand takes place in the same secondary lysosomes as substrate sequestered by autophagic mechanisms. These light lysosomes represent a subgroup of active lysosomes which are gradually recruited from dense bodies. Data are also presented that indicate that insulin may prevent the change in buoyant density brought about by incubation in deficient medium.

Animals↗

PubMed1987

Excess antibody immunoassay for the measurement of tonin in rat tissues and plasma.

Tonin, a proteolytic enzyme isolated from the rat submandibular gland, can generate angiotensin II directly from angiotensinogen. To date a method for the measurement of tonin in plasma has not been available and the present paper describes a sensitive and specific excess antibody immunoassay for determination of tonin in tissue homogenates and plasma. Interference from immunologically cross-reacting proteins was evaluated and the assay was found to be specific for tonin. Tonin measured in various tissue homogenates was directly proportional to the amount of sample added, giving a linear dose-response curve. The slope of this curve was determined by the recovery of tonin, which was better than 55% for urine and all tissues tested. The highest concentration of tonin was seen in the submandibular and sublingual gland (69 and 0.7 microgram/mg protein, respectively). The parotid gland, the exorbital lacrimal gland, liver, kidney, pancreas, and lung contained only negligible amounts (less than 4 ng/mg protein). Tonin in plasma was bound to one major inhibitor with a molecular weight of about 650,000-750,000. A partial splitting of the tonin-inhibitor complex was obtained by preincubating plasma with guanidine, allowing tonin to be measured with a recovery of 38 +/- 13% (n = 16) and with a linear dose-response curve. The concentration of immunoreactive tonin in normal arterial plasma from adult male rats was 0.90 +/- 0.53 ng/ml (n = 16). The concentration decreased after removal of the submandibular glands and increased after sympathetic stimulation.

Animals↗

PubMed1987

Rapid purification of tonin, esterase B, antigen psi and kallikrein from rat submandibular gland by fast protein liquid chromatography.

Tonin, esterase B, antigen psi and kallikrein from the rat submandibular gland were purified by fast protein liquid chromatography with Mono P or Mono Q columns. The purity of the separated proteins was evaluated by sodium dodecyl sulphate polyacrylamide gel electrophoresis and by isoelectrofocusing in flat-bed polyacrylamide gel. Tonin and esterase B were purified by DE-52 cellulose anion-exchange chromatography and chromatofocusing on Mono P in two and three steps, respectively. Antigen psi and kallikrein were purified by a two-step procedure using DE-52 cellulose and Mono Q anion-exchange chromatography. The high resolution power of Mono Q revealed the different isoenzymes of kallikrein.

Animals↗

PubMed1987

Parotid salivary flow in response to mechanical and gustatory stimulation in man.

To examine further the role of the oral receptors in the masticatory-salivary reflex, a study with eight subjects was performed. The influence on mean parotid salivation of combined alterations in frequency and force of chewing and length of the chewing object was evaluated by group comparison. Salivary flow rate was recorded using a sensitive micromanometer, and the frequency (12, 60 and 90 cycles min-1) and force of chewing (10 and 40% of maximum) were controlled by a metronome and masseter muscle EMG, respectively. The maximum instantaneous flow and the latency of the masticatory-salivary reflex were examined in three subjects. For comparison with mean salivation rate during chewing, gustatory stimulation was performed with 0.5 or 5.0% citric acid. The masticatory-salivary reflex was mainly ipsilateral, and depended upon having an object between the teeth. Salivation increased with increases in frequency and force of chewing and with the number of teeth involved, each parameter of chewing having the greatest influence when increased from a low level of action. The salivation response to chewing showed two phases; the first, presumably due to contraction of the myoepithelial cells, had a latency of 0.2-0.4 s, while the second phase occurred about 1 s later. Our results support the hypothesis that the periodontal mechanoreceptors have a major role in the parotid response to chewing. Application of 0.5 and 5.0% citric acid on the back of the tongue induced dose-dependent parotid secretions, significantly higher than those of chewing. A negative correlation was found between the maximum fluid outputs during chewing and 5.0% citric acid stimulation.

Adolescent↗

PubMed1987

Isolation, characterization, and localization of antigen gamma, a serine proteinase of the "kallikrein-family" in the rat submandibular gland.

A trypsin-like serine proteinase, antigen gamma, immunologically partially identical to glandular kallikrein when run against anti-rat glandular kallikrein antiserum in immunoelectrophoresis, was purified from the rat submandibular gland. The enzyme was purified by a two-step chromatography procedure, ionexchange chromatography followed by gel filtration. The criteria for purity were one band in SDS-polyacrylamide gel electrophoresis and in immunoelectrophoresis, respectively. Antigen gamma had a molecular mass of 25,000 Da and consisted of two polypeptide chains with molecular masses of 14,000 and 11,000 Da. The preparation contained several isoenzymes with pI ranging from 4.1 to 4.5. The enzyme showed high specific enzyme activity against the substrate D-valyl-L-leucyl-L-arginine-4-nitroanilide (S-2266), some trypsin-like and kininogenase activity, but no angiotensin converting enzyme, kininase, or tonin activity. Amidolytic activity was increased and stabilized by the presence of detergent in the assay buffer. The pH-optimum of antigen gamma amidolytic activity was about 10. Antigen gamma was inhibited by SBTI and PMSF, whereas aprotinin had to be added in a more than 100 times higher concentration than for glandular kallikrein. The binding pattern of antigen gamma to plasma proteins was different from that of tonin and glandular kallikrein. Antiserum against antigen gamma was raised in rabbits and characterized against rat submandibular gland homogenate. Immunohistochemistry showed antigen gamma in the secretory granules of the submandibular gland granular tubular cells but only adhering to the luminal cell wall in the striated and main excretory ducts. Antigen gamma was not detected in the sublingual or parotid gland or in the kidney. Antigen gamma was demonstrated by immunoelectrophoresis in rat submandibular gland saliva. The concentration was higher in sympathetically than in parasympathetically induced secretion.

Angiotensin-Converting Enzyme Inhibitors↗

PubMed1987

Effect of autonomic nerve stimulation on bleb formation in striated duct cells of the rat submandibular gland.

Several previous investigations have shown that blebs form on the apical surface of the striated duct cells of the rat submandibular gland on feeding after starvation. In the present report the influence of autonomic nerve stimulation on bleb formation was studied by electron microscopy. Both parasympathetic and sympathetic stimulation were performed, using electric nerve stimulation. In addition, sympathetic nerve stimulation in combination with alpha- or beta-adrenergic blockers was used. Massive bleb formation took place in response to sympathetic nerve stimulation. This response was almost completely abolished by the administration of alpha- but not by beta-adrenergic blocker. Bleb formation was not seen after parasympathetic nerve stimulation.

Animals↗

PubMed1987

Endocytosis of acetylated low-density lipoprotein, endothelial cell-modified low-density lipoprotein, and formaldehyde-treated serum albumin by rat liver endothelial cells. Evidence of uptake via a common receptor.

Formaldehyde-treated serum albumin (FSA) and acetylated low-density lipoprotein (Ac-LDL) are taken up in vivo and in vitro by the sinusoidal endothelial cells of the liver. It is not known whether both these ligands are removed by the scavenger receptor. We have studied the effect of increasing concentrations of unlabeled FSA, Ac-LDL, and endothelial cell-modified LDL (Ec-LDL) on the endocytosis of trace amounts of these ligands labeled with 125I. Uptake of 125I-Ac-LDL and 125I-Ec-LDL was strongly inhibited by FSA. Likewise, Ac-LDL and Ec-LDL reduced the uptake of 125I-FSA effectively. Our data indicate that these modified LDLs and FSA are bound to and internalized via the same receptor on liver endothelial cells.

Acetylation↗

PubMed1987

Pulmonary and testicular angiotensin-converting isoenzymes.

A variant of angiotensin-converting enzyme occurs in (male) germinal cells. This testicular isozyme is catalytically similar to the widespread pulmonary-type isozyme, but contains a shorter polypeptide chain and does not appear until puberty. The two proteins differ at their NH2- and COOH-termini, but share many tryptic peptides. All antigenic determinants of the testicular form are represented in the pulmonary molecule whereas the latter contains determinants unrelated to catalysis which are lacking in the testicular species. The data indicate that the testicular isozyme corresponds closely to an internal part of the pulmonary polypeptide which includes its active site. The structural and developmental differences between the two polypeptides are pretranslationally determined since they are demonstrable in a cell-free system programmed by the appropriate mRNAs. Characterization of the molecular mechanisms responsible for the relationship of these isozymes may yield useful information regarding cell-specific protein expression.

Animals↗

PubMed1987

Tissue uptake of biologically modified low density lipoprotein in the rat.

Human low density lipoprotein (LDL) was modified by exposure to cultured human endothelial cells. The endothelial cell modified LDL (EC-LDL) and control LDL (con LDL) labelled with 125I-tyramincellobiose (125I-TC) were injected into rats. Since 125I-TC is trapped in lysosomes the contribution of various organs to the catabolism of EC-LDL and con LDL could be studied. First, EC-LDL was cleared from plasma several times faster than con LDL. Then, the liver was found to be the major organ for catabolism of EC-LDL. Con LDL was distributed more evenly among the spleen, liver and adrenals as the main organs. In the liver the endothelial cells were most effective in degrading EC-LDL whereas con LDL was distributed approximately evenly between the Kupffer, endothelial and parenchymal cells. Thus, the liver endothelial cells seem to be a major pathway for catabolism of modified LDL.

Animals↗

PubMed1986

Uptake, intracellular transport and release of 125I-poly(vinylpyrrolidone) and [14C]-sucrose-asialofetuin in rat liver parenchymal cells. Effects of ammonia on the intracellular transport.

We have studied the intracellular transport of 125I-labeled poly(vinylpyrrolidone) (125I-PVP) and [14C]sucrose-asialofetuin (14C-SAF) in isolated rat hepatocytes. 125I-PVP and 14C-SAF are taken up in the cells by fluid phase and receptor-mediated endocytosis, respectively. The labeled degradation products formed from 14C-SAF are trapped in the lysosomes. They can therefore serve as markers for lysosomes in subcellular fractionation studies. The accumulation of 125I-PVP in the cells was rapid initially and then decreased to a constant value. The diminished rate of accumulation was due to release (exocytosis) of previously endocytosed 125I-PVP. The release of 125I-PVP was studied in cells that had accumulated 125I-PVP for various times and then after washing incubated in new medium at 37 degrees. About 25% of the radioactivity associated with the cells after 1 hr was released to the medium subsequently. No such release was observed in cells that had taken up 14C-SAF. Subcellular distribution of 125I-PVP and 14C-SAF was studied by isopycnic centrifugation in sucrose gradients. Both compounds were sequentially associated with light (1.13 g/ml) and dense (1.19 g/ml) vesicles. Exocytosed 125I-PVP was derived from the light vesicles. The denser organelles were probably lysosomes as their distribution coincided with that of lysosomal enzymes. By measuring radioactivity soluble and precipitable in trichloroacetic acid it could be shown that only degraded 14C-SAF was associated with lysosomes. Undegraded 14C-SAF was associated with vesicles banding at 1.13 g/ml. Degraded 14C-SAF was, however, also seen first in this region of the gradient, suggesting that degradation started in a light lysosome. Both uptake and release of 125I-PVP were temperature dependent; both processes ceased at 10 degrees. Ammonium ions had negligible effects on uptake and release of 125I-PVP. The amine inhibited, however, the transfer of both 125I-PVP and 14C-SAF to the lysosomes.

Acetylglucosaminidase↗

PubMed1986

Receptor mediated endocytosis of formaldehyde treated albumin, yeast invertase and chondroitin sulfate in suspensions of rat liver endothelial cells.

Isolated rat liver endothelial cells take up and degrade formaldehyde serum albumin (FSA), invertase and chondroitin sulfate (CS) efficiently. Degradation products start to appear in the medium after 5-30 min. Calcium was necessary for binding of invertase to the cells, but not for the two other ligands. Ammonia and monensin inhibited uptake as well as degradation of all three ligands, whereas leupeptin only inhibited the degradation of FSA and invertase. Uptake of CS was strongly inhibited in the presence of 1 microM FSA. The possibility that these two ligands bind to a common receptor is discussed.

Animals↗