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Biomedical subjects

W Gevers

Publications and source records attributed to W Gevers.

At least 55 records · Page 3Linked to original sources
PubMed1982

The metabolic response to squash including the influence of pre-exercise carbohydrate ingestion.

Serum glucose, free fatty acid, insulin and growth hormone values, blood lactate levels and changes in body weight and rectal temperature were measured in 6 squash players during two separate 90-minute matches, one of which started 25 minutes after the players had ingested 67 g carbohydrate. Serum glucose, growth hormone and blood lactate levels rose during both matches, reaching peak values after 45 minutes, whereas serum free fatty acid levels rose progressively and insulin levels fell. The mean weight loss was 2 kg and the mean post-match rectal temperature was 39 degrees C. Pre-exercise carbohydrate ingestion caused serum insulin and growth hormone concentrations to be significantly higher during the first half of the match. Glucose and free fatty acid levels were lower, but not significantly so, during exercise after carbohydrate ingestion. Neither weight loss nor rectal temperature ws influenced by pre-exercise carbohydrate feeding. We conclude that the thermal and metabolic response to squash is similar to that to moderate-intensity running and is characterized by hyperthermia, hyperglycaemia, elevated free fatty acid and growth hormone levels and low blood lactate and serum insulin values. In these players pre-exercise carbohydrate feeding did not produce adverse metabolic effects, possibly because the players had enhanced glucose tolerance, characterized by a diminished insulin response to ingested carbohydrate. This is likely to be associated with a high degree of endurance adaptation. Nevertheless, the lower serum glucose and free fatty acid levels indicate that pre-exercise carbohydrate feeding impairs the normal metabolic response to squash and may adversely affect performance, particularly in poorly trained players. Players should therefore be discouraged from ingesting high-carbohydrate foods or drinks shortly before playing squash or taking part in other similar activities.

Adult↗
PubMed1982

Loss of type I procollagen gene expression in SV40-transformed human fibroblasts is accompanied by hypermethylation of these genes.

Transformation of human lung fibroblasts (WI-38) by Simian Virus 40 (SV40) resulted in a decline of 25-30% in the amount of secreted collagen. The collagen produced by the transformed fibroblasts contained no type I collagen (i.e. alpha 1(I) and alpha 2 chains), which was the major collagen component produced by untransformed fibroblasts. Measurement of the procollagen mRNA levels by dot hybridization with nick-translated procollagen-cDNA clones showed that the absence of type I collagen was due to the absence of alpha 1(I) and alpha 2 procollagen mRNAs. This result was confirmed by hybridization of cDNA to total RNA with southern blots of the procollagen clones. To clarify the mechanism by which type I procollagen gene transcription is abolished in transformed cells, the methylation patterns of the alpha 1(I) and alpha 2 procollagen genes in normal and SV40-transformed fibroblasts were compared, using the chicken alpha 1(I) and alpha 2 procollagen-cDNA clones as probes. Methylated sites were detected by means of the restriction endonuclease isoschizomers HpaII and MspI. Methylation of the procollagen alpha 1(I) and alpha 2 genes was increased in the SV40-transformed fibroblasts, concurrently with the loss of type I collagen synthesis. DNA methylation may thus contribute to altered regulation of gene expression upon cell transformation.

Cell Line↗
PubMed1981

Retro-endocytosis of low density lipoprotein by cultured bovine aortic smooth muscle cells.

Cultured bovine aortic smooth muscle cells, pretreated with 125I-labelled low density lipoprotein (LDL), rapidly released significant amounts of the lipoprotein as trichloroacetic acid-precipitable material during a subsequent chase period. The time and temperature dependence of this release process and its insensitivity to heparin-pretreatment of equilibrated cells suggest that LDL was regurgitated from cells by a rapid process that we have termed 'retro-endocytosis'. The total amount of lipoprotein released from cells equilibrated at 37 degrees C with 125I-labelled LDL was approximately 20% of the amount degraded, pointing to the existence of a small pool of material which was distinct from the lysosomal pathway. To quantify the flux of LDL through retro-endocytosis, the fate of surface-bound lipoproteins was analyzed. Cells, pretreated with 125I-labelled LDL at 4 degrees C, regurgitated about 50% of the initial surface-bound LDL during a chase period at 37 degrees C and degraded the remainder more slowly through the lysosomal pathway. The involvement of LDL-receptors was implicated because retro-endocytosis was a saturable process and was affected by up- and down-regulation. The apolipoprotein of the released LDL showed little proteolytic modification as analyzed by gel filtration. We conclude that in a steady-state situation the fraction of LDL that passes through the retro-endocytosis pathway is of the same order as that which is directed through the lysosomal system.

Animals↗
PubMed1981

Effects of three prostaglandin analogues on lysosomal enzyme activities and ultrastructural morphology of luteal cells in the chacma baboon.

The effects were studied of three different prostaglandin analogues on lysosomal cathepsin D and acid phosphatase activities in the corpus luteum of the chacma baboon (Papio ursinus). Lysosomal latency was found to be increased by these agents, as well as the total particulate activities of both enzymes. A comparison of total post-treatment cathepsin D values with control values showed a significant increase in activity with time; this did not apply to acid phosphatase. Concomitant electron microscopic studies showed a higher cellular content of lysosomes, consistent with the greater particulate activities recorded. Definitive evidence of progressive ultrastructural changes was consistently found in corpora lutea from prostaglandin analogue-treated baboons. It is proposed that the mechanism of luteolysis induced by prostaglandin analogues in this primate species is based on induction of the formation of primary lysosomes which cause cellular degeneration through autosegregation and enzymatic digestion of cell organelles in secondary lysosomes.

Acid Phosphatase↗
PubMed1981

Metabolic alterations in cancer. Part II. Protein and fat metabolism.

Intracellular changes in protein metabolism within cancer cells may facilitate cell reduplication, and this may be supported by changes in enzymes responsible for protein synthesis and degradation. Synthesis of ectopic hormones probably reflects genetic de-repression. Increased muscle proteolysis has been reported by some workers in cancer patients, and this may be associated with muscle cells, increased glucocorticoid secretion by the adrenal cortex, increased gluconeogenesis or impaired muscle glycolysis. Decreased proteogenesis has also been reported to occur in the muscles of cancer patients. Although tumour tissue may inhibit muscle proteogenesis, there are as yet no data to suggest a direct tumour-derived ectopic substance which affects muscle proteolysis or proteogenesis. Data regarding serum levels of free fatty acids (FFA) in weight-losing cancer patients are conflicting, although it is likely that abnormally high values are due to liver dysfunction rather than enhanced peripheral lipolysis. Nevertheless, since serum levels may be normal if FFA consumption is increased to the same extent as release, these levels need not indicate overall FFA turnover. If enhanced FFA release from fat stores does occur, this may provide the liver with an energy source required for its increased commitment to gluconeogenesis.

Animals↗
PubMed1981

Metabolic alterations in cancer. Part I. Carbohydrate metabolism.

Glucose intolerance seen in weight-losing patients may not result from qualitative or quantitative alterations in insulin secretion or binding. It may, however, be the result of increased gluconeogenic flux which occurs in these patients. This may be due to increased substrate availability resulting from lactate production as the unoxidized-end-product of tumour glycolysis (Warburg effect). In addition, increased levels of glucogenic amino acid may be associated with preferential amino acid sequestration by the tumour, causing decreased muscle proteogenesis and therefore atrophy. Enhanced glucose demand by tumour cells may also lead to an increased hepatic gluconeogenesis, as will the production of ectopic ACTH.

Acetyl Coenzyme A↗
PubMed1981

Calcium: the managing director. The regulatory role and the regulation of calcium fluxes in living cells.

Calcium ions exert important controlling influences in various compartments of living cells; fluxes across the membrane barriers around and within cells are thus highly regulated. Ca2+-binding proteins such as calmodulin act as transducers and affect a large variety of processes in rapidly reversible ways. Adrenergic mechanisms in the heart and in smooth muscle illustrate these concepts.

Animals↗
PubMed1980

Cathepsin-D-dependent initiation of the hydrolysis by lysosomal enzymes of apoprotein B from low-density lipoproteins.

The degradation of 135I-apoprotein B of human low-density lipoprotein by cell extracts of cultured bovine aortic smooth muscle cells was determined by measuring the formation of acid-soluble products and by analyzing the electrophoretic patterns of digested apoprotein in gels containing sodium dodecyl sulfate. Degradation resulted in an initial rapid accumulation of a limited number of distinct smaller fragments. Two products with apparent molecular weights of 220,000 and 200,000 predominated. Pepstatin inhibited proteolysis almost completely, as measured by either assay. Leupeptin decreased hydrolysis to acid-soluble products by approximately 50%, but had no effect on the initial cleavage of intact apoprotein B. Similar results were found in the case of extracts from cultured human skin fibroblasts and from adult bovine arterial smooth muscle. Leupeptin inhibited intracellular degradation of 125I-apoprotein B in cultured cells by approximately 50%. It is concluded that the intralysosomal degradation of apoprotein B involves an initial limited endoproteolytic attack at susceptible sites by cathepsin D. This and other enzymes, including cathepsin B, then act synergistically to bring degradation to completion.

Animals↗
PubMed1980

Biochemical and electrophoretic properties of acid phosphatase isozymes and their distribution in cell functions from neoplastic prostatic tissues.

The various acid phosphatase isozymes can be distinguished on the basis of their biochemical properties or their net electrical charge. Four main groups of isozymes hydrolyze beta-glycerophosphate: the fastest-moving form seemed to be related to the cancerous state. The quantity of enzyme, either in the whole homogenate or in cytoplasmic fractions was not a useful criteria for cancer, however, while the distribution of acid phosphatase in subcellular structures was characteristic in cancer cases. Cell fractions were obtained by differential centrifugation, but were contaminated with prostatic secretions.

Acid Phosphatase↗
PubMed1980

[Possibilities for the evaluation of receptor sites in benign prostatic hyperplasia and carcinoma of the prostate (author's transl)].

Cytoplasmic and nuclear receptor sites of the prostate will be determined for a qualitative information about the pattern of specific bindings. Their qualitative evaluation and their selective suppression will give an idea about the hormonal influence and regulation in prostatic tissue. These investigations are performed in some cases of prostatic cancer. The difficulty of tissue preparation is caused by the individual distribution of collagen tissue in prostatic cancer which will decide the yield of purified receptor sites. Besides the elemination of unspecific binding sites like SHBG and albumin is an evidence for the value of a method. According to high amount of binding sites the most effective preparation of patients before a tissue biopsy is discussed. For the clinical application the DCC test in case of cytoplasmic sites and the exchange test for nuclear sites seem to provide a suitable method. Performing gelfiltration and additional test with denatured material is necessary because of the similar size of SHBG and receptor complexes interfering the results.

Binding Sites↗
PubMed1980

Plasmin-treated low density lipoproteins: polypeptide analyses and metabolism by cultured smooth muscle cells.

Plasmin, generated by the interaction of urokinase with plasminogen, degraded the apoprotein B moiety of human low density lipoprotein to yield distinct high moleculr weight intermediates under conditions where only a small fraction (less than 3%) of the protein was hydrolyzed to trichloroacetic acid-soluble products. The molecular weights of these intermediates were between 60 000 and 200 000 as estimated by SDS-polyacrylamide electrophoresis. Trypsin treatment yielded fragments of similar size to those obtained with plasmin. When enzyme-treated low density lipoproteins were added to bovine aortic smooth muscle cells in culture, the receptor-binding, and rates of internalization and degradation were no different from those obtained in the case of native low density lipoproteins.

Animals↗
PubMed1979

Cardiac myofibrillar phosphorylation and adenosine triphosphatase activity.

When myofibrils from rat hearts were dissolved in concentrated salt solutions and reprecipitated by dilution, they contained both protein kinase (partly cyclic 3':5'-AMP-dependent) and protein phosphatase activities. Troponin-I was the major protein to be phosphorylated by the endogenous myofibril-associated kinase and by added protein kinase. Approximately 1 mole of phosphate per mole of troponin-I was incorporated from radioactive ATP, but the extent of troponin-I phosphorylation could be varied experimentally. An inverse correlation was found between protein phosphorylation and the maximum Ca2+-stimulated myofibrillar Mg2+-ATPase activity, while the amout of calcium required for half-maximum activation was proportional to the extent of protein phosphorylation. The changes in Mg2+-ATPase activity produced in vitro by protein phosphorylation were reproduced in isolated perfused rat hearts treated for short periods with L-noradrenaline (10(-6)M). The changes in myofibrillar function brought about as the result of the phosphorlyation by cAMP-dependent protein kinase suggest that the contractile response is desensitized in order to cope with the rise in intracellular Ca2+ which results from the action of catecholamines on cardiac ventricular cells.

Adenosine Triphosphatases↗