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Biomedical subjects

S Knospe

Publications and source records attributed to S Knospe.

At least 37 records · Page 2Linked to original sources
PubMed1984

Antibody-dependent cell-mediated cytotoxicity of mononuclear cells against Langerhans islets of Wistar rats in normal man and in patients at diabetes risk.

Antibody-dependent cell-mediated cytotoxicity against pancreatic islets was investigated in 13 newly diagnosed insulin-dependent diabetics, in 38 patients at high risk for the disease and in 20 age-matched healthy controls. For this purpose 51Cr-labeled neonatal rat pancreatic islets incubated with the specific anti-rat islet cell antiserum 339 or with serum of the lymphocyte donors were used as targets. The antibody-mediated cytotoxic activity of mononuclear cells was evaluated from the specific chromium release after 6 h exposure of pretreated islets to the effector cells. The specific cytotoxic effect of mononuclear cells from healthy controls on pancreatic islets pretreated with serum is weak. ADCC mediated by the specific antirat islet cell antiserum is significantly increased in 54% of newly diagnosed diabetics as well as in 32% of patients at high risk for insulin-dependent diabetes mellitus. 46% of the newly diagnosed diabetics were also ADCC-positive when their own serum was used for the pretreatment of islets, regardless of whether they were islet cell antibody- or islet cell surface antibody positive or not. Subsets of mononuclear cells (non E-rosette-forming cells, high affinity E-rosette-forming cells, low affinity E-rosette-forming cells) were prepared and their cytotoxic potential was analysed in patients with positive ADCC test results.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗
PubMed1983

Protection of insulin secretion by magnesium during islet culture: independence of cAMP/or insulin accumulation.

Pancreatic rat islets cultured for 12 days maintained their insulin content and biosynthesis when cultivated at 10 mmol/l glucose. The glucose-induced insulin secretion investigated in a subsequent incubation period was, however, reduced. At a Mg++ concentration of 5.3 mmol/l in the tissue culture medium not only the content and biosynthesis, but also the secretory response of cultured islets remained fully preserved compared to freshly isolated islets. The secretory response of pancreatic islets cultured at 0.8 or 5.3 mmol/l Mg++ for 4 days was neither related to steady state concentrations of cAMP nor connected to the cAMP accumulation in response to IBMX. The results demonstrated that the favourable effect of Mg++ during a culture period on the subsequent insulin release is not directly related to hormone storage, synthesis and/or cAMP-accumulation.

1-Methyl-3-isobutylxanthine↗
PubMed1982

Carp insulin: amino acid sequence, biological activity and structural properties.

The amino acid sequence of insulin of carp (Cyprinus carpio) has been determined and correlated with its biological activity in a fat-cell test and its structural properties as measured by circular dichroism and sedimentation analysis. The amino acid sequence of carp insulin displays some unusual features: the B chain is longer at the N terminus by two residues as compared with mammalian insulins and there are substitutions of the charged residues, found in most insulins at positions B21 and B22, by proline and threonine respectively. On the other hand, all amino acid residues essential for biological activity and for the association of insulin monomers are the same in carp insulin. Accordingly, the half-maximal response in a fat-cell test is reached with carp insulin at concentrations which are only three times higher than with porcine insulin and the maximal response is the same. The circular dichroism spectrum of carp insulin resembles greatly that of bovine insulin indicating that it has a similar spatial structure. Despite amino acid substitutions in the dimer-dimer contact region, carp insulin is able to form hexamers.

Adipose Tissue↗
PubMed1981

Impaired hormonal regulation of adenosine 3',5'-monophosphate release in adipose tissue from hyperglycemic sand rats in vitro.

Egyptian sand rats (Psammomys obesus) developed under laboratory holding conditions and in dependence of different food intake various states of hyperglycemia and hyperinsulinism. Associated with the development of this syndrome insulin resistance of muscle- and adipose tissue appears. The question arose as to whether hyperglycemia and hyperinsulinism generally leads to hormone resistance. Therefore, we selected sand rats with different degrees of hyperglycemia and various stages of hyperinsulinism. Two groups of sand rats were investigated: normoglycemic and hyperglycemic animals. In these sand rats the catecholamine action on cAMP production adipose tissue was studied in vitro. There was a significant reduction of hormone responsiveness in adipose tissue of the hyperglycemic group compared with the noradrenaline response of adipose tissue of the normoglycemic sand rats. In no case had insulin significantly inhibited the noradrenaline stimulated cAMP production. By means of adenosine deaminase studies the interference of the eventual release of adenosine with the hormone action on adipose tissue in vitro could be excluded. In the sand rats correlations between IRI levels in the decapitation blood and noradrenaline stimulated cAMP release associated with simultaneous occurrence of insulin- and catecholamine resistance in adipose tissue seem to indicate that hormone resistance could be a general phenomenon during the development of hyperinsulinism.

Adipose Tissue↗
PubMed1981

A specific method of high sensitivity for the determination of adenosine in the incubation medium of fat tissue.

A suitable method for the measurement of adenosine in the incubation medium of fat tissue (200-500 mg) has been developed. The method is based on the specificity of the adenosine deaminase reaction and on the high sensitivity of a fluorescent method for adenine derivatives. The decrease of fluorescence in a sample after treatment with this enzyme is used for measuring adenosine in the range of 50-500 pmoles/tube. This method is highly specific and is not affected by other adenine derivatives present in the sample. Instead of acetic acid, perchloric acid was used in the fluorescent reaction, thus increasing the amount of adenosine dependent fluorescence. With this modification of the original fluorescent method, perchloric acid extracts can be used without further processing after deproteinization of the samples. Using this method, we could measure the adenosine release of fat pads of Wistar rats incubated in Krebs-Ringer-albumin buffer without concentration or purification procedures.

Adenosine↗
PubMed1981

Significance of adenosine for the hormone responsiveness of adenylate cyclase in adipose tissue of normoglycemic and hyperglycemic sand rats.

In young sand rats, bred in our colony, the metabolism was directed from the normoglycemic state by means of feeding conditions. The noradrenaline action on adenylate cyclase is impaired in hyperglycemic, hyperinsulinemic sand rats. Generally, addition of adenosine to the in vitro system eliminates the responsiveness of the adenylate cyclase to noradrenaline in adipose tissue. The presence of adenosine deaminase in the incubation medium abolished this inhibition effect of added adenosine. The interference of released adenosine with the hormone action in vitro was excluded by addition of adenosine deaminase to the incubation medium. In both groups of sand rats adenosine deaminase did not increase the noradrenaline effect on adenylate cyclase. Investigations were carried out as a part of the research project "Diabetes mellitus and diseases of fat metabolism". These results along with the others on the measured adenosine release exclude adenosine as a reason for the disturbed hormone action on adenylate cyclase in hyperglycemic, hyperinsulinemic sand rats.

Adenosine↗
PubMed1980

[Radioligand assay: methods and application. V. Mono-125I-insulin: preparation and immunological and biological characterization].

A reproducible method for preparation of 125I-monoiodoinsulin with fully biological activity was developed. Monoiodoinsulin has been prepared from a heterogeneous 125I-iodination mixture by anion exchange chromatography on DEAE-Sephadex A-25 without using any gradient elution technique. The specific radioactivity of 125I-monoiodoinsulin was calculated to 14.3 +/- 0.8 TBq/g, i.e. an iodine content of 1.04 +/- 0.06 atoms per molecule of insulin. Monoiodoinsulin was indistinguishable from native insulin with respect to binding to guinea pig anti-insulin serum, and to insulin receptors of isolated rat adipocytes. The biological potency (96.5 +/- 7.5 per cent of the immunoreactive insulin activity) determined by the conversion of [14C1]-D-glucose to 14CO2 in vitro by rat fat cells was not significantly different from that of native insulin.

Animals↗
PubMed1979

Insulin sensitivity of non-obese asymptomatic diabetics in vivo in relation to insulin responsiveness of their adipose tissue in vitro.

In twenty-four non-obese male subjects a 2-hour glucose infusion test (12 mg/kg/min) with initial bolus injection (0.33 g/kg) was performed as a test of carbohydrate tolerance. Sixteen individuals had a normal and eight a pathological carbohydrate tolerance (asymptomatic diabetes). All subjects received a one-hour insulin infusion (two 30-minutes periods of 8 or 16 mU/kg MC-Actrapid). After two days subcutaneous adipose tissue was removed from the abdominal wall by needle biopsy for characterization of insulin-stimulated (1-14C) glucose incorporation into triglycerides. Under in vivo conditions insulin provoked a decrease of blood glucose concentrations by 31 +/- 3.9% and 11.6 +/- 2.2% as well as of plasma free fatty acids levels by 60 +/- 4.6% and 37 +/- 6.8% in normal persons and asymptomatic diabetics, respectively (p less than 0.01). In vitro the insulin-stimulated incorporation of labeled glucose into triglycerides of adipose tissue was diminished in asymptomatic diabetics. Thus, the results indicate that both the in vivo insulin responsiveness and the in vitro insulin sensitivity of adipose tissue are reduced in early stages of diabetes. The findings suggest that changes in insulin target tissues are equally important in the development of carbohydrate intolerance in non-obese subjects.

Adipose Tissue↗
PubMed1978

Preparation and characterization of insulin of carp (Cyprinus carpio).

Insulin of carp (Cyprinus carpio) was isolated and crystallized. The insulin was biologically active in two tests; it decreased the blood glucose level and stimulated 14CO2-formation from glucose. The chemical properties are similar to those of insulins from other species. The insulins of carp and of mammals differ greatly immunologically. Antibodies against carp insulin crossreact with carp proinsulin.

Amino Acids↗
PubMed1978

The response to insulin by adipose tissue of insulin-dependent diabetics in vitro.

Subcutaneous adipose tissue was removed by surgical biopsy from 10 normal subjects and 4 insulin-dependent diabetics under exact intracutaneous anaesthesia. The adipose tissue fragments or isolated fat cells were incubated with a tracer amount of labeled glucose. In the presence of insulin (62.5 muU/ml) the production of carbon dioxide from glucose by adipose tissue fragments of nonobese controls as well as diabetics increased up to 286 +/- 62% and 198 +/- 14.7%, respectively. Furthermore, triglyceride synthesis was raised to 257 +/- 30% and 267 +/- 34%, respectively. There were no differences in the sensitivity of adipose tissue to insulin of healthy volunteers and juvenile diabetics.

Adipose Tissue↗
PubMed1978

[Insulin binding to isolated cells].

Using mono-125I-insulin the hormone receptor binding on cultivated rat hepatocytes cultivated rat fibroblasts and freshly isolated adipocytes of wistar rat and man were characterized. No specific insulin binding was obtained in the case of long time cultivated hepatocytes. The fibroblasts show a low specific insulin binding with an affinity constant of K = 0.75. 10(9)M-1 and a binding capacity of q = 4000 binding sites per cell, and also an insulin response measureable by the lactate production. In agreement with a strong stimulation effect of insulin on the conversion of glucose to CO2 und triglycerides the freshly isolated adipocytes bind insulin with high affinity and capacity in comparison with the fibroblasts. For the high affinity population of insulin receptors at the adipocytes of wistar rat we found K = 2.8 . 10(9) M-1 and q = 22000 binding sites per cell, whereas 20 per cent of saturation of the receptors cause 90 per cent of the maximal stimulation effect on the bio-conversion of glucose. This shift of the binding curve to higher concentrations may be important for the ability of insulin to regulate the carbohydrate metabolism.

Adipose Tissue↗
PubMed1977

[Obesity as a metabolic risk factor].

On the basis of the results of clinico-experimental examinations and of animal experiments the importance of obesity as metabolic factor of risk is confirmed and hereby the diabetes mellitus as well as cardiovascular effects are particularly taken into consideration. Conclusions are made relevant to practice and it is particularly referred to the central position of the B-cells for the pathogenesis of diabetes as well as to prophylactic and early therapeutic measures.

Adult↗
PubMed1977

Insulin and glucagon secretion and the insulin sensitivity of peripheric organs of colony-bred sand rats fed with pellet diet after weaning.

Colony-bred sand rats were fed with rat pellet chow in restricted quantities or ad libitum for 8--10 or 28--31 weeks after weaning. The changes of glucose metabolism were characterized by an intraperitoneal glucose tolerance test. The daily food intake and the average weight gain differed only in the first 5--7 weeks of pellet nutrition. In the impaired glucose tolerance tests of all sand rats the high basal plasma IRI levels were not significantly increased by the grossly enhanced blood glucose concentrations. The insulin secretion of either acutely incubated or for 8 days cultivated isolated pancreatic islets, however, was stimulated already by low (1.7 and 5 mM) glucose concentrations in all diet groups. Otherwise the glucagon secretion of isolated islets was not suppressed by high glucose concentrations. No changes of insulin or glucagon contents of islets were found in the different diet groups. The adipocytes of all animals revealed a complete ineffectiveness of insulin on the glucose utilization to CO2 and triglycerides. The basal glucose conversion to CO2 and glycogen in skeletal muscle and the stimulatory potency of insulin was low and not distinctly different in all groups. In liver glycogen and triglyceride contents as well as gluconeogenic enzyme activities were not influenced by feeding of different quantities of pellet diet at the investigated time points. The time course of the metabolic and clinical alterations demonstrates that the peripheral organs become insensitive to insulin in the first weeks after weaning.

Animals↗
PubMed1977

Variations of glucose utilization in muscle and adipose tissue of sand rats (Psammomys obesus) during adaptation to laboratory holding.

Sand rats, captured in Egypt and fed with a low caloric vegetable diet during adaptation, were investigated before and after 2.5 and 8 weeks diet treatment (30 and 40 kcal/100 g body weight daily). In hexobarbital anaesthesia the sand rats were loaded with 1 g glucose/kg body weight in a single dose intravenously. After a rapid increase the content of glucose in blood remained at a level of about 600 mg glucose/100 ml blood. The insulin immunoreactivity in blood did not change uniformly after application of glucose and remained in a physiologic range. In the islets of Langerhans a degranulation was found during diet treatment. The sensitivity of the epididymal adipose tissue towards insulin in vitro decreased to a nearly complete resistance in the course of diet treatment. A diminution of insulin sensitivity was also found in the m. soleus in vitro. The content of glucose-6-phosphate in the m. semimembranosus was found enhanced after the preparation of the animal. It was found progressively increased up to the five-fold at the end of diet treatment. In the corresponding muscle the glucose distribution volume was increased to about double the extracellular volume. An accumulation of free glucose within the muscle cell must be taken into account. In conclusion the treatment of sand rats with a diabetogenic diet results very quickly in a loss of insulin sensitivity of adipose tissue. The progressively increased stress-mediated accumulation of glucose-6-phosphate and free glucose refers to an inhibition of glucose utilization in the phosphorylation step of glucose in skeletal muscle.

Adipose Tissue↗
PubMed1976

Investigations on isolated islets of Langerhans in vitro. XIV. Insulin secretion and insulin stores of cultivated islets from sand rats (Psammomys obesus): investigations of glucose-dose response.

Release of immunoreactive insulin activity (IRI) and biological insulin like activity (ILA) from collagenase isolated pancreatic islets of sand rats (Psammomys obesus) maintained on a vegetable diet were examined at 60 min and 24-48 h intervals under culture conditions at 1.0 and 15.6 mM glucose. The glucose-insulin dose response curves for sand rats after 60 min incubation were compared with those after 24 or 48 h of incubation. The pancreatic islets responded to 5mM glucose with a high insulin release especially under culture conditions. A drastic depletion of stored insulin in the islets cultivated for 2 days at 5 or 15 mM glucose is accompanied by a continuous diminution of the glucose-induced insulin release with the prolongation of cultivation up to one week.

Animals↗