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Biomedical subjects

G Schettler

Publications and source records attributed to G Schettler.

At least 55 records · Page 3Linked to original sources
PubMed1985

Visualization of the hepatic low-density lipoprotein receptor in rats by sequential scintiscans.

The usefulness of a gamma camera system for external imaging of the degradation sites of low-density lipoprotein (LDL) is demonstrated in rats. [131I]LDL was injected intravenously in normal rats and rats pretreated with 17 alpha-ethinyl estradiol for LDL receptor induction. Distribution of the radioligand was followed for 20 min, for perfusion control [131I]albumin was administered. Rats pretreated with 17 alpha-ethinyl estradiol showed a marked increase in the LDL uptake by the liver, which was not competed by the preinjection of physiological amounts of unlabelled LDL. It is concluded that the injection of small amounts of [131I]LDL is sufficient to image the hepatic LDL receptor and that the endogenous LDL does not compete effectively at physiological LDL levels.

Animals↗
PubMed1985

[Eicosanoids and phospholipases].

Prostaglandins, thromboxanes, and leukotrienes have been implicated to play an important role in physiology as well as in a growing list of pathophysiologic conditions. These oxidation products of 8.11.14-eicosatrienoic-, 5.8.11.14.-eicosatetraenoic-, and 5.8.11.14.17.-pentaenoic acids have been collectively designated eicosanoids. Many clinically important diseases are associated with altered eicosanoid biosynthesis. Furthermore, a series of hormones are known to induce acutely formation of eicosanoids, suggesting a crucial role in a multitude of tissue responses including phenomena such as secretion, platelet aggregation, chemotaxis, and smooth muscle contraction. The major precursor for the eicosanoids seems to be 5.8.11.14.-eicosatetraenoic acid or arachidonic acid. Virtually all of arachidonic acid however is present in esterified form in complex glycerolipids. Since cyclooxygenase and the lipoxygenases utilize arachidonic acid in its free form, a set of acylhydrolases is required to liberate arachidonic acid from membrane lipids before eicosanoid formation can occur. It became only recently apparent that a minor acidic phospholipid, phosphatidylinositol, comprising only 5%-10% of the phospholipid mass in mammalian cells, plays an important role in arachidonic acid metabolism. Phosphatidylinositol--after phosphorylation to phosphatidylinositolphosphate and phosphatidylinositolbisphosphate--appears to be hydrolyzed by specific phospholipases C generating 1-stearoyl-2-arachidonoyl-diglyceride. Diglyceride serves as substrate for diglyceride lipase to form monoglyceride and free fatty acid. Alternatively diglyceride is phosphorylated by diglyceride kinase yielding phosphatidic acid, which is believed to be reincorporated into phosphatidylinositol. In addition to phosphatidylinositol phosphatidylcholine, phosphatidylethanolamine and phosphatidic acid may contribute to arachidonic acid release. These phospholipids are substrates for phospholipases A2 generating free arachidonic acid and the respective lysophospholipid. Understanding of the biochemistry of arachidonic acid liberation may be critical in developing strategies of pharmacological intervention in a variety of pathological conditions.

Animals↗
PubMed1985

The effects of a combination of cigarette smoking and oral contraception on coagulation and fibrinolysis in human females.

Oral contraception as well as cigarette smoking influence haemostasis. The simultaneous effect of both on blood coagulation and fibrinolysis was studied in nine female smokers. While continuing oral contraception after a 4-week abstinence from smoking the concentration of fibrinogen, antithrombin III and alpha 1-Antitrypsin decreased (P less than 0.01 or P less than 0.04) and of plasminogen increased (P less than 0.03). The other coagulation parameters remained unchanged. Although all determinations of these parameters were in the normal range, the observed trends were statistically significant. The concentrations of the fibrinopeptide A and B 15-42 did not differ. It is concluded that the observed alteration is caused by cessation from cigarette smoking.

Adult↗
PubMed1985

Cell cycle-dependent changes in arachidonic acid and glycerol metabolism in Swiss 3T3 cells stimulated by platelet-derived growth factor.

Quiescent Swiss 3T3 cells stimulated to divide by human platelet-derived growth factor (PDGF) were used to investigate cell cycle-dependent changes in arachidonic acid, stearic acid, and glycerol metabolism. PDGF at 12 ng/ml stimulated incorporation of labeled arachidonic and stearic acid into phosphatidic acid and phosphatidylinositol within 60 min. With similar kinetics PDGF stimulated glycerol incorporation into phosphatidic acid and phosphatidylinositol indicating early growth factor-dependent stimulation of de novo phosphatidylinositol synthesis. This early effect of PDGF was specific for the phosphatidylinositol synthesis pathway since no comparable changes were noted in other glycerolipids. After a lag of 4-6 h, PDGF strongly stimulated arachidonic acid incorporation into triacylglycerol: at 6 h, arachidonate radioactivity in triacylglycerol exceeded that in phosphatidylcholine, phosphatidylethanolamine, and phosphatidylinositol. This effect of PDGF was not associated with de novo triacylglycerol synthesis since no increase in the rate of glycerol incorporation into this lipid was noted. Finally, PDGF stimulated incorporation of glycerol into all major phospholipids and triacylglycerol during S-phase. These results disclose three novel effects of PDGF on glycerolipid metabolism in Swiss 3T3 cells: 1) early selective activation of the phosphatidylinositol synthesis pathway; 2) delayed strong stimulation of arachidonic acid incorporation into triacylglycerol; and 3) late induction of de novo phosphatidylcholine, phosphatidylethanolamine, and triacylglycerol synthesis. These PDGF effects are likely to play important roles in phosphatidylinositol metabolism, membrane biosynthesis, and fatty acid turnover in rapidly growing cells.

Animals↗
PubMed1985

Characterization of binding sites for acetylated low density lipoprotein in the rat liver in vivo and in vitro.

Acetylated low density lipoprotein (acetyl-LDL) binding to hepatic membrane proteins of rats was analysed in vitro by ligand blotting. Specific binding could be demonstrated to two hepatic proteins with an apparent mol. wt. of 250 kd and 220 kd. Polyanionic competitors and maleylated bovine serum albumin inhibited the binding of acetyl-LDL effectively. To determine the sites of the catabolism of acetyl-LDL, [131I]-acetyl-LDL was injected intravenously into control rats and rats pre-treated with the known competitors of the acetyl-LDL binding. Distribution of the radiolabelled acetyl-LDL was followed by a scintillation camera. Six minutes after injection, the radioactivity was concentrated in the liver. The competitors and unlabelled acetyl-LDL but not native LDL reduced the hepatic uptake of [131I]acetyl-LDL dramatically. Thus, the sensitivity of the 220- and 250-kd membrane binding sites to the competitors for the acetyl-LDL binding resembled that of the hepatic compartment in vivo. Finally, an application of scintigraphy with radiolabelled low density lipoproteins for diagnostic evaluation of tumor compartments is presented.

Animals↗
PubMed1985

The effect of nicotine on cultured cells of vascular origin.

Monolayers of endothelial, smooth muscle and fibroblastic cells of healthy porcine, bovine or human fetal origin were treated with 10(-4) to 10(-9) M final concentrations of nicotine. The effect was registered as changes in the synthesis and polyimerization of the cytoskeleton. The silver and gold impregnation method produced anisotropy of the synthetic granules and of the final polymers of microtubules and filaments under physiological conditions as revealed by polarization microscopy. Since the orientation of the cells was inhomogeneous in the cultures, the organization of the orientation was expressed as the sum of alternative diagonal and orthogonal measuring of anisotropy by a computerized microraster morphometry system joined to an OPTON cytophotometer. The 8-day-old control and treated cultures were also examined by electronmicroscopy. Nicotine stimulated the synthesis and polyimerization of the cytoskeletal protein. This phenomenon is evident in smooth muscle cells, and partly also in endothelium. Fibroblasts were not influenced by the doses of nicotine tested.

Animals↗
PubMed1985

Human platelet-derived growth factor stimulates prostaglandin synthesis by activation and by rapid de novo synthesis of cyclooxygenase.

Human platelet-derived growth factor (PDGF) stimulated prostaglandin (PG) E2 synthesis in the cell cycle of Swiss 3T3 cells at two distinct time intervals, with a first plateau within 10 min and a second plateau within 2-4 h after addition of PDGF. At 4 h, the concentration of PGE2 in PDGF-stimulated cultures exceeded the quiescent control cells by a factor of 10-15. Quiescent cells incubated with up to 16 microM exogenous arachidonic acid (AA) synthesized only small amounts of PGE2. In contrast, 4 h after addition of PDGF, the concentration of PGE2 synthesized from exogenous AA exceeded that in quiescent cultures by a factor of 28. The effect of PDGF stimulation on PG synthesis from exogenous AA could not be explained by growth factor-mediated increase in the cellular free AA pool as shown in experiments using [14C]AA. PDGF also stimulated synthesis of PGI2 (prostacyclin), thromboxane, and PGF2 alpha from exogenous AA. While inhibition of protein synthesis by 10 micrograms/ml cycloheximide had no effect on the early increase in PGE2 synthesis, the second increase was completely prevented. Additionally, cycloheximide treatment at 6 h after PDGF stimulation resulted in rapid decline of PGE2 synthesis from exogenous AA. Quiescent cultures pretreated with 100 microM aspirin and stimulated by PDGF thereafter recovered from cyclooxygenase inhibition within 180 min. Our results suggest that phospholipase activation and resultant AA release is not sufficient to induce the burst of PG synthesis observed in PDGF-stimulated cells. Instead, PDGF stimulates PG synthesis by direct effects on the PG-synthesizing enzyme system, one involving a protein synthesis-independent mechanism and another that requires rapid translation of cyclooxygenase.

Arachidonic Acid↗
PubMed1985

The low density lipoprotein and low density lipoprotein receptors and their possible importance in the pathogenesis of atherosclerosis.

In man and in experimental animals, elevations in plasma cholesterol lead to premature atherosclerosis. It is likely that the cholesterol-rich low density lipoprotein (LDL) plays a keyrole in atherogenesis. LDL accumulates in patients with familial hypercholesterolemia (FH), a genetic syndrome associated with a defective LDL receptor in parenchymal cells and premature atherosclerosis. Monocytic/macrophage-like cells invading the vessel wall are becoming enriched with cholesteryl ester and concentrating in the early atherosclerotic lesion. Modification of LDL stimulates the uptake of cholesterol by macrophages in vitro leading to the conversion of the cells to lipid laden foam cells. Because of this phenomenon recent investigations were focussing on the lipid metabolism of macrophages. In vitro studies have demonstrated that macrophages have specific cell surface receptors for modified forms of LDL. It was suggested that these scavenger receptors could mediate foam cell formation in vivo, too. In vivo analysis by sequential scintiscans revealed that the liver is accumulating most actively modified LDL, possibly acting as a sieve for atherogenic lipoproteins. The putative liver receptor for modified (= atherogenic) LDL was characterized as a membrane protein of 220 000 to 250 000 D by ligand blotting.

Acetylation↗
PubMed1984

A simple and rapid anti-ligand enzyme immunoassay for visualization of low-density lipoprotein membrane receptors.

Triton X-114 was used to solubilize the membrane proteins of bovine adrenal cortex and human leukocytes. The solubilized membrane proteins were subjected to electrophoresis and transblotted to nitrocellulose paper and incubated with LDL/acetyl-LDL. The combination of peroxidase-conjugated second antibody and 4-chloronaphthol/H2O2 allowed rapid development of colored bands where LDL or acetyl-LDL bound to electroblotted proteins. The ELISA is highly sensitive and efficient for screening a large number of samples and avoids the need for a continuous supply of radiolabeled antibodies and autoradiography.

Adrenal Cortex↗