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Biomedical subjects

R Lammers

Publications and source records attributed to R Lammers.

66 records · Page 4Linked to original sources
PubMed1989

Intermolecular transphosphorylation between insulin receptors and EGF-insulin receptor chimerae.

The insulin receptor, a glycoprotein consisting of two extracellular alpha- and two transmembrane beta-subunits, is thought to mediate hormone action by means of its tyrosine-specific protein kinase activity. To explore the mechanism of insulin receptor phosphorylation we have used NIH3T3 cells transfected with two receptor constructs: one encoding a chimeric receptor composed of the extracellular domain of the human EGF receptor and the cytosolic domain of the human insulin receptor beta-subunit, and a second construct encoding a kinase-defiecient human insulin receptor. Stimulation of these cells with EGF induced tyrosine autophosphorylation of the EGF-insulin receptor chimera (150 kd) and tyrosine phosphorylation of the beta-subunit of the kinase-deficient insulin receptor (95 kd). The phosphopeptides of the autophosphorylated cytoplasmic domain of the EGF-insulin receptor chimera were comparable to those of the transphosphorylated beta-subunit of the kinase-deficient insulin receptor and of the wild-type human insulin receptor. When immunoaffinity purified EGF-insulin receptor hybrids and kinase-deficient insulin receptors were used in a cell lysate phosphorylation assay, it was found that addition of EGF produced 32P-labeling of both receptor species. We conclude that EGF acting directly through the EGF-insulin receptor chimera causes transphosphorylation of the kinase-deficient insulin receptor. These data support the notion that autophosphorylation of the insulin receptor may proceed by an intermolecular mechanism.

Animals↗
PubMed1989

Inhibition of hepatic cholesterol synthesis by the alpha 1-adrenoceptor blocker doxazosin in the hypercholesterolemic golden hamster.

The effect of treatment with the alpha 1-specific adrenoceptor blocker, Doxazosin, on lipid parameters was studied in male Golden hamsters fed a cholesterol-enriched diet. Within 1 week the Doxazosin-treated animals had a lower plasma (-12%) and hepatic (-30%) cholesterol content than the cholesterol-fed controls. De novo cholesterol synthesis in the liver was lowered by 39% in the Doxazosin-treated animals. These data indicate that the reported beneficial effect of alpha 1-blockade on plasma cholesterol levels may be due to lowering of the hepatic cholesterol synthesis.

Acetates↗
PubMed1989

Effects of doxazosin on lipids, lipoprotein lipases, and cholesterol synthesis in the golden hamster.

The effects of treatment with adrenoceptor blockers on sites regulating lipid metabolism were studied in golden hamsters. In hamsters fed a standard chow, doxazosin, propranolol, and atenolol did not affect plasma cholesterol or triglycerides. After hypercholesterolemia was induced by feeding a cholesterol-enriched diet, doxazosin lowered plasma cholesterol by 12%. Lipoprotein lipase activity in adipose tissue and in the heart was not changed by any of the treatments. Hepatic lipase activity in the liver and blood was lowered by 31% in the doxazosin-treated animals. Hepatic cholesterol synthesis, measured as acetate incorporation into cholesterol and hydroxymethylglutaryl coenzyme A (HMG-CoA) reductase activity, was also lowered in the doxazosin-treated hamsters. After norepinephrine administration to cholesterol-fed hamsters, atenolol increased (+8%) and doxazosin decreased (-35%) plasma triglycerides. Plasma cholesterol levels and hepatic cholesterol synthesis were no longer significantly affected by doxazosin. In norepinephrine-treated animals, adipose tissue lipoprotein lipase activity was enhanced (+30%) by doxazosin. Hepatic lipase activity in plasma and liver, which was lowered by norepinephrine, was increased by doxazosin. In hamsters not treated with norepinephrine, adrenoceptor blockers had no effect on plasma insulin or thyroid hormone, but with norepinephrine, levels of both insulin and thyroid hormone were increased by doxazosin. These data indicate that selective alpha 1-inhibition with doxazosin may interfere with lipid metabolism at several regulatory sites. The effects depend to a large extent on nutritional and hormonal status. Doxazosin might exert these effects partly via influences on other hormones.

Adrenergic alpha-Antagonists↗
PubMed1988

Alternative mechanisms for gene activation induced by poly(rI).poly(rC) and Newcastle disease virus.

After poly(rI).poly(rC) induction of FS-4 fibroblasts, both human interferon-beta (IFN-beta) mRNA and an additional induced RNA class (12S RNA) hybridize to a genomic cosmid clone containing the human IFN-beta gene as well as 35 kbp of flanking sequences. However, this coinduced 12S RNA does not originate from regions in the neighborhood of the IFN-beta gene, but hybridizes to the genomic cosmid clone via repetitive Alu-family sequences. While IFN-beta mRNA rapidly decays after reaching a maximum 2-4 h after induction, this 12S RNA is stably maintained in the fibroblast cell for more than 16 h. Contrary to IFN-beta mRNA, the level of the 12S RNA is not further elevated by superinduction conditions (cycloheximide treatment) during poly(rI).poly(rC) induction. However, subsequent to treatment with the weaker viral inducer Newcastle disease virus (NDV) both IFN-beta and the 12S RNA transcripts are induced to a higher level in the presence of cycloheximide. Cell-free translation of hybrid-selected 12S RNA leads to detection of an induced protein of 14 kDa. cDNA cloning reveals that the 12S RNA contains part of an Alu-family sequence in the 5'-untranslated region. The 12S RNA is probably not an RNA polymerase III transcript and codes for a protein of 9 kDa (as monitored by in vitro cell-free translation). This discrepancy in molecular mass can be attributed to a retarded migration of the protein in SDS/PAGE.

Amanitins↗
PubMed1987

Effects of synacthen on lipid metabolism in the perfused epididymal fat pad of the rat.

Rats were treated with Synacthen, a synthetic corticotrophin analogue, to induce hypercorticism. The epididymal fat pad was selectively cannulated and perfused. In fasted rats acetone ether powder lipoprotein lipase (LPL) activity rose during treatment to levels found in fed controls. In fed animals no further rise in LPL activity was observed during Synacthen treatment. However, the heparin-elutable LPL activity did not change during this treatment in fasted nor fed animals. Pharmacologic levels of insulin in the perfusion medium caused an increase in heparin-releasable LPL activity as a percentage of total fat pad LPL activity (15% v 48%). Hydrolysis of chylomicrons was higher in fasted three days treated animals then in controls (10 +/- 4% v 2 +/- 2%). In this group a higher uptake of liberated free fatty acids was found (2.6 +/- 1.5% v 1.0 +/- 0.5% in controls). The increase in hydrolysis rate and uptake of fatty acids in the treated fasted animals could not be explained by an increase in releasable LPL activity. Fatty acid release from the fat pad was lower in treated animals than in controls (fasted and fed), basally as well as after adrenalin stimulation. The observation that the epididymal fat pad retains its weight during hypercorticism may therefore be ascribed to an increased influx of fatty acids from increased hydrolysis of TG-rich particles and to an inhibited efflux of fatty acids from the adipocyte. The discrepancy between the LPL activity extractable from an acetone ether powder and the heparin releasable LPL activity suggests impairment of the transport of LPL from the adipocyte to the heparin releasable pool at the endothelium.

Adipose Tissue↗
PubMed1987

Disparate effects of ACTH (1-24) and corticosterone on lipoprotein lipase in rat adipose tissue.

The effects of corticosterone and ACTH(1-24) on lipoprotein lipase (LPL) activity of rat epididymal fat tissue were studied. Hypercorticism induced by s.c. administration of 10 mg corticosterone acetate for 3 days led to a decrease in LPL activity. This decrease could be prevented by treatment of the rats simultaneously with synthetic ACTH(1-24). Adrenalectomy also reduced LPL activity. Corticosterone and ACTH(1-24) treatment had a similar effect on LPL activity in adrenalectomized and intact rats. These results indicate that ACTH(1-24) may affect adipose tissue LPL in the rat by a mechanism in which corticosterone is not involved.

Adipose Tissue↗
PubMed1986

Enhancement of translational efficiency by the Escherichia coli atpE translational initiation region: its fusion with two human genes.

The cDNA sequences encoding mature human interleukin 2 (IL2) and beta-interferon (INF beta), respectively, were fused with various translational initiation regions and inserted into two different types of expression vector. The relative levels of expression of the two genes and the functional stability of their respective mRNAs were examined in vivo in Escherichia coli hosts. The addition of the 30-bp sequence, found immediately upstream of the E. coli atpE gene Shine-Dalgarno (SD) sequence, to the translational initiation regions of IL2 and INF beta increased the expression of both these genes by a factor of 6-10. Thus this sequence, which naturally acts within the E. coli atp operon to enhance the translational initiation frequency of the atpE gene, can increase the expression of other genes in E. coli. It may exemplify a specific type of recognition signal for the E. coli translational apparatus.

Base Sequence↗
PubMed1986

[The social network of schizophrenic patients].

First, the literature is reviewed under three different perspectives: the role of social networks as etiological factor, the impact of the illness on the social relationships of the patients, and the influence of social networks on the course of schizophrenic disorders. Then, results of an empirical study of social relationships of schizophrenic patients, using the 'Interview Schedule for Social Interaction' developed by Henderson et al., are presented. Compared to the ideal norm as well as to normal people and other patient groups the social network of schizophrenic patients showed marked deficits.

Adult↗
PubMed1985

The effect of Synacthen administration on lipoprotein lipase activity in the epididymal fat pad of the rat.

Conflicting data have been reported on the influence of (excess) glucocorticoids on lipoprotein lipase (LPL) activity in adipose tissue. To solve this problem hypercorticism was induced in rats by treatment for varying periods with Synacthen, a synthetic corticotrophin-1-24 preparation, and LPL was measured in the epididymal fat pads using different methods. In extracts of defatted tissue preparations from overnight fasted rats treated for 3 days with Synacthen we observed an increase in LPL activity (acetone-ether powder LPL) to values similar to those found in normally fed controls. In contrast, the heparin-elutable part of LPL activity in the tissue was not influenced by the Synacthen treatment. This activity remained significantly lower in overnight fasted animals, Synacthen treated or not, than in normally fed rats. Adrenalectomy lowered the acetone-ether powder LPL activity of the epididymal adipose tissue in fasted as well as in fed rats. In fasted rats it prevented the stimulation of the LPL activity by Synacthen.

Adipose Tissue↗
PubMed1978

Triglyceride turnover in severe chronic non-nephrotic renal failure.

In 12 patients with chronic non-nephrotic renal failure (creatinine clearance 3.5-11 ml/min) and 8 control subjects, plasma triglyceride turnover was studied. The patients showed significantly increased fasting triglyceride concentrations and absolute plasma triglyceride turnover rates, while the fractional turnover rate was significantly decreased. The finding of an elevated triglyceride turnover rate with a near normal fractional removal rate in the patients with the highest creatinine clearance suggests the involvement of an increased triglyceride synthesis rate in these patients. However, most patients showed an impaired removal mechanism as the major cause of the hypertriglyceridemia.

Adult↗
PubMedDate not supplied

Inability of patients to self-diagnose wound infections.

At the time of follow-up wound inspection or suture removal, 433 patients were questioned about signs of wound infection. Patients' answers were compared to evaluations by medical examiners. Patients frequently failed to recognize infection and signs of inflammation. When asked if wound infection was present, patients' false positive diagnostic rate was only 8%, but the false negative diagnostic rate was 48%. Medical examiners diagnosed wound infection in 21 wounds, and patients correctly identified their infections in only 11 of these cases. These results indicate that for the population studied, patients cannot be expected to recognize infection in their own wounds using verbal or printed instructions. Clinical investigators of wound healing should not use patient-reported data about wound infection that is obtained by telephone interview or other means.

Adolescent↗