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Biomedical subjects

M Grün

Publications and source records attributed to M Grün.

At least 19 recordsLinked to original sources
PubMed2000

Synthesis of spherical porous silicas in the micron and submicron size range: challenges and opportunities for miniaturized high-resolution chromatographic and electrokinetic separations.

Classical silica technology has reached its limit with respect to an ultimate minimum particle size of about 2 microm in diameter. Here, a novel process is presented which allows one to synthesize porous silica beads and control their particle diameter in situ, within the range of 0.2-2.0 microm. As a result, no sizing is required and losses of silica are avoided. Furthermore, the process enables one to control in situ the pore structural parameters and the surface chemistry of the silica beads. Even though surface funtionalized silicas made according to this process can principally be applied in fast HPLC the column pressure drop will be high even for short columns. In addition, the column efficiency, expressed in terms of the theoretical plate height is about H-2d(p) in the best case and limited by the A and C term of the Van Deemter equation. In other words the gain in total plate number when using 1-2 microm silica beads in short columns is minimal as compared to longer columns packed with 5 microm particles. Capillary electrochromatography (CEC) as a hybrid method enables the application of micron size as well as submicron size particles. This consequently enhances column efficiency by a factor of 5-10 when compared to HPLC. The use of short CEC columns packed with submicron size silicas provides the basis for fast and efficient miniaturized systems. The most significant feature of CEC as compared to HPLC is that the former allows one to resolve polar and ionic analytes in a single run. An alternative method for miniaturization is capillary electrophoresis (CE) which generates extremely high efficiencies combined with fast analysis. Its application, however, is limited to ionic substances.

Chromatography, Liquid↗
PubMed1998

Pore Size Analysis of MCM-41 Type Adsorbents by Means of Nitrogen and Argon Adsorption.

Methods of nonlocal density functional theory (NLDFT), proposed recently for predictions of adsorption equilibrium and calculations of pore size distributions in micro- and mesoporous materials, were tested on reference MCM-41 materials. Five newly synthesized MCM-41 adsorbents with presumably uniform pore channels varying from 32 to 45 Å were characterized by X-ray diffraction (XRD), nitrogen adsorption at 77 K, and argon adsorption at 77 and 87 K. New sets of intermolecular interaction parameters of the NLDFT model for N2 and Ar adsorption on MCM-41 were determined. The parameters were specified to reproduce the bulk liquid-gas equilibrium densities and pressures, liquid-gas interfacial tensions, and standard adsorption isotherms on nonporous surfaces in the multilayer adsorption region. The pore size distributions calculated from the desorption branches of the experimental isotherms measured at three different temperatures were consistent with each other. Comparison of the NLDFT-calculated pore sizes with XRD data showed that the thickness of pore walls in the MCM-41 samples under consideration varied from ca. 6 to 12 Å. We found no correlation between the pore size and the pore wall thickness. The results obtained support the NLDFT model as a suitable tool for characterizing nanoporous materials and predicting adsorption equilibrium. The MCM-41 samples studied can be used as references for adsorption measurements. Copyright 1998 Academic Press.

Journal Article↗
PubMed1994

Influence of type of diet and incubation time on in sacco release of Cu, Fe, Mn and Zn from Italian ryegrass, untreated and ammonia treated wheat straw.

Artificially dried ryegrass, untreated and ammonia-treated wheat straw were ground and incubated in nylon bags in the rumen of three sheep each fed with diets based on roughage or concentrate. Dry matter degradability, the concentration and the release of the trace elements Cu, Fe, Mn and Zn from the incubated feeds were measured after 0 (washing loss), 6, 12, 24, 48 and 72 h rumen incubation time. Dry matter degradability, trace element concentration and their release were significantly influenced by the kind of incubated feeds, incubation time and feeding of sheep. Cu- (1.8-6.9 mg kg-1 DM) and Zn concentrations (36-103 mg kg-1 DM) of straw residues in the bags were much higher than those of original straw (1.2-1.6 and 8.1-9.9 mg kg-1 DM resp.). The inflow of Cu and Zn in the bags containing straw residues was higher than their release. The Cu-, Fe- and Mn-release from ryegrass was similar to the dry matter degradability, but the Zn-release was much lower.

Ammonia↗
PubMed1991

Portacaval shunt as an experimental model of impaired hepatic release of vitamin A in liver disease.

Vitamin A concentrations in serum and liver were studied in rats with a portacaval shunt for 48 days after shunt surgery. In addition, serum and tissue concentrations of zinc were analyzed. Following portacaval shunting serum vitamin A concentration decreased to 25% of the level in sham-operated controls, whereas serum zinc concentration decreased to 80%. The mean urinary excretion rate of zinc increased in shunted rats [18.7 +/- 2.1 micrograms/day (0.28 +/- 0.03 mumol/day)] compared with controls [13.8 +/- 1.7 micrograms/day (0.21 +/- 0.03 mumol/day)] (P less than 0.01). The concentration of retinol and total retinoids in liver tissue increased 2-3-fold in rats with a portacaval shunt, and the ratio of retinol to retinoids was slightly increased. The differences were reduced when the total organ content was calculated, because of the reduced liver weight in the shunted rats. The concentration of zinc in liver tissue decreased in rats with portacaval shunts [30.8 +/- 4.9 micrograms/g wet wt (0.47 +/- 0.07 mumol/g) vs. 35.6 +/- 3.7 micrograms/g wet wt (0.54 +/- 0.06 mumol/g) in controls; P less than 0.01]. The concentration of zinc was inversely correlated with retinol (r = -0.52, P less than 0.05) and total retinoid levels (r = -0.70, P less than 0.05) in rats with portacaval shunts but not in controls. The data are consistent with the hypothesis of an impaired release of vitamin A from the liver in rats with portacaval shunts, an impairment that could be due to liver zinc deficiency.

Animals↗
PubMed1990

[Autoradiography determination of the GABA(A) receptor density in the brain of rats with portacaval shunt].

Quantitative autoradiography was used to assess the densities of gamma-aminobutyric acid (GABAA) receptors in the brains of rats with a portacaval end-to-side shunt (PCA). The shunt alone induced only mild encephalopathy with ataxia and decreased locomotion. Aggravation of the encephalopathy was achieved by gavage feeding of packed erythrocytes or by induction of severe hyperammonemia by intraperitoneal injection of urease. Gavage feeding of erythrocytes led to severe encephalopathy in about 50% of the animals with PCA. The combination of PCA and urease treatment caused severe encephalopathy in every animal. The serum ammonia concentration increased 5 times normal by PCA alone, 20 times normal by gavage feeding of erythrocytes and more than 30 times normal by urease-treatment of the PCA-animals. For autoradiography, coronal slices were cut at the level of the hippocampal formation and through the cerebellum. Radioligand binding was measured using as a ligand 3H-muscimol, a specific GABAA receptor agonist. The specific binding of 3H-muscimol was assessed densitometrically in several microregions of cerebral cortex, hippocampus and cerebellar cortex. No significant differences were observed between the magnitude of ligand binding to specific microregions of brains from normal animals, animals with PCA without overt encephalopathy and animals with severe encephalopathy induced by a combination of PCA and gavage feeding of erythrocytes or urease treatment.

Ammonia↗
PubMed1989

[Ileus symptoms due to 3 distinctively differentiated small intestine carcinomas in nontropical sprue].

Recently recurring abdominal pain, bouts of diarrhoea and weight-loss of 15 kg developed in a 50-year-old woman who had for 18 years been treated by diet for nontropical sprue. She was hospitalized for signs of mechanical ileus. Radiological examination revealed three stenosing small intestine tumours, one of them obstructing the lumen. After resection of the affected segments, with end-to-end anastomosis, histological, histological examination of the surgical specimens demonstrated three small intestine carcinomas of different grades of differentiation. The largest tumour had already metastasized to four regional lymph nodes. This case illustrates the potentially precancerous nature of nontropical sprue which has been present for many years and thus requires careful follow-up.

Adenocarcinoma↗
PubMed1989

Increased bioavailability of enzymes of eicosanoid synthesis in hepatic and extrahepatic tissues after portacaval shunting.

Metabolites of arachidonic acid have been attributed to severe circulatory, metabolic and hormonal alterations in patients with chronic liver disease. In order to study changes of the tissue-specific availability of enzymes of eicosanoid synthesis, we used portacaval-shunted rats, as this model exhibits many clinical and biochemical similarities to patients suffering from cirrhosis of the liver. Microsomal mass and maximal velocity of prostaglandin H synthase, the initial enzyme of prostaglandin synthesis, were markedly and permanently increased after shunting in both hepatic and extrahepatic tissues as compared to those of sham-operated rats. Maximal velocity of thromboxane synthase and prostacyclin synthase, two more peripheral enzymes of the arachidonic acid cascade, were tissue-specifically enhanced, whereas the apparent affinities (Km) remained unchanged. Determination of 5-lipoxygenase activity in tissue preparations disclosed a preferential increase in the liver, lung and renal cortex after portacaval shunting. Furthermore, exposure to endotoxin closely mimicked the shunting-induced changes. These results suggest that after portacaval shunting and possibly in patients with advanced liver disease, profound abnormalities at the level of local enzyme expression might play a pathophysiologically important role in the control of eicosanoid synthesis.

6-Ketoprostaglandin F1 alpha↗
PubMed1989

The lead status of horses from central Europe depending on breed, sex, age and living area.

The breed of horses took a significant effect on the Pb content of animals with a normal Pb supply. Warm-blooded horses stored more Pb in skeleton, kidneys, liver and cerebrum than heavy horses. The sex only had the trend of influencing the Pb status. Mares with a normal Pb supply incorporated more Pb than geldings. Age only took a slight effect on the skeleton. Older horses stored more Pb in the metatarsal bone than younger ones. The Pb content of horse meat was not influenced by Pb exposure. Pb was not additionally deposited in the musculature. The Pb offer of the living area took a significant effect on the Pb status of horses. Skeleton, liver and kidneys indicated the site-specific influences significantly.

Aging↗
PubMed1989

[Hyperestrogenemia following various shunt operations: on the role of estrogens in the development of focal nodular hyperplasia of the liver].

Hormones especially estrogens have been suspected to induce liver cell tumours or hepatic focal nodular hyperplasia (FNH). In rats 6 months after portocaval anastomosis (PCA) the occurrence of FNH has been observed. Modified portocaval anastomosis (mPCA) does not lead to FNH. To test the concept of estrogen induced tumour formation we measured in both groups as well as in a shamoperated control group (SOP) the levels of estradiol (E2), estrone (E1) and of testosterone (T). In a further experiment the hormone levels were measured in rats with portocaval transposition (PCT), an operation which leads to high gonadal hormone production. In groups of 6 male rats each (280-300 g) either SOP, PCA, mPCA or PCT were performed. 30 days later the blood levels of E2, E1, and of T were measured by radioimmunoassay. In PCT-rats hormone levels were measured in the blood synchronously taken from the inferior vena cava (prehepatic) and from the heart (posthepatic), to get an information of the hepatic hormone degradation. After PCA the median level of E2 (77 pg/ml) and E1 (63 pg/ml) are significantly elevated when compared with SOP-rats (41 and 43 pg/ml). Equally after mPCA the E2 and E1 levels are significantly higher (61 and 70 pg/ml) than in controls rats. In contrast the concentrations of T are significantly reduced (PCA 0.03, mPCA 0, 10, SOP 1.0 ng/ml). PCA as well as mPCA result in a hyperestrogenic and hypoandrogenic status. When PCA and mPCA are compared, only the testosterone blood levels are significantly different.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1987

Bladder carcinogenesis in portacaval shunt rats.

The induction of transitional cell bladder tumors following portacaval shunt (PCA) in rats was investigated. Thirty-five (29 males; 6 females) out of 86 animals developed a carcinoma. The highest incidence of tumors (73%) was seen in control animals without a PCA but with implantation of a bladder stone. PCA rats had an induction rate of 34% and a spontaneous bladder tumor was seen in 2/13 sham-operated controls. All rats with a bladder tumor also had urolithiasis; 34 rats had bladder stones in 1 rat had kidney stones. The induction rate in males was 29/52, 55.7% compared to 6/34, 17.6% in females. All tumors were transitional cell carcinomas and were graded G0-GIII [1(G0); 24 (GI); 1 (GI-II); 9 (GII)] accompanied in 20 cases by squamous cell metaplasia. Chronic irritation by stones and infection are the most likely causes of tumor development; however, other mechanisms such as excretion of carcinogens or tumor promoters cannot be completely excluded. The sex difference in stone formation - and tumor induction - are subject to further investigations.

Animals↗
PubMed1986

Hepatitis A-like non-A, non-B hepatitis: light and electron microscopic observations of three cases.

To date, three types of NANBH have been distinguished by epidemiological, clinical and experimental data. We examined the liver biopsies of three patients with an acute NANBH resembling hepatitis A from the infection route, incubation period and clinical course. The liver biopsies revealed lesions with a portal and periportal predominance, thus also exhibiting parallels with hepatitis A on the histopathological level.

Adult↗
PubMed1984

Neoplastic surface changes in urothelium of rats after portacaval anastomosis. A combined light and scanning electron microscopic study.

The development of preneoplastic and neoplastic alterations in the urinary tract was investigated by light and scanning electron microscopy in rats after portacaval anastomosis. The changes consisted of slight hyperplasia to papillary hyperplasia after 24 weeks. Carcinomas were present in all animals after 52 weeks. Surface characteristics can be correlated with the sequence of changes in urothelial cells. Short uniform microvilli appear in moderate hyperplasia and a cobblestone formation of the cells is typical of papillary hyperplasia. In transitional cell carcinomas the cells varied in shape and size and they were densely covered with pleomorphic microvilli. Although the cause of tumour induction after portacaval anastomosis is not clearly understood, possible mechanisms are discussed.

Animals↗
PubMed1984

Nickel--an essential element.

Nickel is necessary for the biosynthesis of the hydrogenase, carbon monoxide dehydrogenase, and of factor F 430, found in a number of genera of bacteria. Urease from jack beans and several species of plants is also a nickel protein. These plant enzyme systems can affect animals via the microbiological digestion of food in the rumen. Nickel is a constituent part of all organs of vertebrates. Its absorption can be controlled. Low nickel offers reduce growth; this is particularly true of intra-uterine development. Such offers also decrease the life expectancy of reproducing animals. Nickel deficiency is accompanied by histological and biochemical changes and reduced iron resorption and leads to anaemia. It can disturb the incorporation of calcium into skeleton and lead to parakeratosis-like damage, which finds expression in disturbed zinc metabolism. Nickel deficiency results in lower activities of different dehydrogenases and transaminases and, above all, of alpha-amylase, and particularly affects carbohydrate metabolism. A marked decrease in metabolism was observed in the case of the energy sources fat, glucose, and glycogen. Nickel therefore performs a vital function in metabolism: it is an essential element. The nickel requirements of human beings and animals amount to less than 500 micrograms/kg and are probably even considerably lower. It therefore follows that, in view of the available nickel offer, primary nickel deficiency in human beings and animals can be excluded, at least in the present state of knowledge. On the other hand, it should be remembered that, 25 years after the discovery of the essentiality of manganese, this element was included among the trace elements of academic importance only, whereas today it is a feed additive.

Aldehyde Oxidoreductases↗
PubMed1984

Ultrastructural characteristics of hyperplastic alterations in the liver of congenital portacaval-shunt rats.

A congenital portacaval shunt was discovered in five rats. In these animals the hepatic artery was the only blood vessel perfusing the liver; the portal vein was absent. The livers were small and mainly hypoplastic, but light microscopy revealed the occurrence of focal hyperplastic alterations and occasional hyperplastic nodules. TEM and SEM showed these areas to be composed of clustered hepatocytes, separated by widened intercellular spaces. The cell membranes carried numerous pleomorphic microvilli, and the cytoplasma contained densely packed mitochondria, some of which were giant sized. Liver cells in the centrilobular region were hypoplastic. Comparison with findings of experimental portacaval anastomosis suggest that in congenital-shunt animals, the overall hypoplasia of the liver with the formation of hyperplastic areas is a consequence of the lack of portal blood.

Animals↗
PubMed1984

[Sex hormones and fertility following portacaval anastomosis in rats].

Portocaval anastomosis (PCA) in the normal male rat causes profound alterations in testicular morphology and function and in plasma levels of sex steroids as well as of gonadotropins. Testicular atrophy is accompanied by a significant decrease of plasma testosterone (0.03 ng/ml versus 0.99 ng/ml) and an increase of estradiol (76.2 pg/ml versus 39.7 pg/ml) and estrone (68. pg/ml versus 45.5 pg/ml). Plasma levels of gonadotropins (LH, FSH) and prolactin are lowered too (LH: 15 ng/ml versus 28.5 ng/ml, FSH:119 versus 182 ng/ml, prolactin:53 versus 109 ng/ml). The altered sex hormone metabolism is reflected in marked changes of the morphology and nucleic acid content of the metabolizing organs i.e. liver, gonades and kidney. The results of this study are consistent with the hypothesis that portosystemic shunt per se plays an important role in the pathogenesis of the disturbed metabolism of sex hormones observed in patients with liver cirrhosis and portal hypertension.

Adrenal Glands↗