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Biomedical subjects

U Keller

Publications and source records attributed to U Keller.

At least 217 records · Page 12Linked to original sources
PubMed1988

Genetics of actinomycin C production in Streptomyces chrysomallus.

Three distinct classes of mutations affecting the biosynthesis of actinomycin have been established in Streptomyces chyrsomallus by crossing various actinomycin-nonproducing mutants with each other by protoplast fusion. In crosses between members of different classes of mutations, actinomycin-producing recombinant progeny arose, whereas in crosses between members of the same class, no actinomycin-producing recombinants were seen. Biochemical examination of a number of mutants revealed that the expression of all actinomycin synthetases was reduced by about 1 order of magnitude in mutants belonging to class II. In mutants of class I, the specific activities of the actinomycin synthetases were comparable with those measured in their actinomycin-producing parents. Feeding experiments with 4-methyl-3-hydroxyanthranilic acid (4-MHA), the biosynthetic precursor of the chromophore moiety of actinomycin, with representative mutants of the three genetic classes revealed formation of actinomycin in minute amounts by mutants of class I. It is suggested that mutants belonging to class I are mutated at a genetic locus involved in the biosynthesis of 4-MHA. Mutants belonging to class II appear to carry mutations at a locus involved in the regulation of the expression of the actinomycin synthetases. The role of the locus in class III mutations could not be assigned. Mapping studies in S. chrysomallus based on conjugal matings revealed the chromosomal linkage of all three loci. Mutations belonging to classes I and III were closely linked. Their genetic loci could be localized in a map interval of the chromosomal linkage group which is significantly distant from the gene locus represented by mutations belonging to class II.

Dactinomycin↗
PubMed1988

Effect of calcitonin and calcitonin gene-related peptide on pancreatic functions in man.

Calcitonin gene-related peptide (CGRP) has recently been identified in central and peripheral nerve fibres, including those of blood vessels supplying the exocrine pancreas, and in pancreatic islet cells. Moreover, receptors have been characterised in the same tissue. The present study examined the effects of human CGRP and of calcitonin on exocrine pancreatic secretion and on islet cell function in nine healthy volunteers. CGRP (300 ng/kg/h) caused, respectively, a 25% and 31% inhibition of caerulein stimulated trypsin and amylase output which was similar to that seen with calcitonin (300 ng/kg/h). Arginine stimulated insulin and glucagon release was unaffected by either CGRP, or calcitonin. Calcitonin gene-related peptide caused cutaneous flushing, but did not affect the pulse rate or arterial blood pressure in the doses tested. Calcitonin gene-related peptide inhibits exocrine pancreatic secretion in vivo in man, but does not affect islet cell hormone release.

Adult↗
PubMed1988

Fatty acid-independent inhibition of hepatic ketone body production by insulin in humans.

To investigate whether elevated plasma insulin or glucagon concentrations are capable of modifying hepatic ketogenesis independently of plasma free fatty acid (FFA) concentrations, ketone body production was determined by [3-14C]acetoacetate infusions in overnight-fasted normal subjects during exogenous supply of FFA (Intralipid and heparin infusion). When plasma FFA concentrations were elevated from 0.73 +/- 0.07 to 1.53 +/- 0.16 mmol/l during low insulin concentrations (approximately equal to 13 microU/ml) in group A (n = 7), total ketone body production increased from 3.6 +/- 0.6 to 8.2 +/- 1.0 mumol.kg-1.min-1 (P less than 0.001). When plasma FFA were similarly elevated during raised plasma insulin concentrations (approximately equal to 110 microU/ml) in group B (n = 5), total ketone body production was only 3.8 +/- 0.8 mumol.kg-1.min-1 (P less than 0.01 vs. group A). Low plasma FFA and low insulin concentrations resulted in total ketone body production of 0.70 +/- 0.18 mumol.kg-1.min-1 in group C (n = 7; P less than 0.01 vs. groups A and B). Elevation of plasma glucagon during Intralipid infusion in group D (n = 7) failed to affect ketogenesis, but the beta-hydroxybutyrate-to-acetoacetate concentration ratio decreased significantly (P less than 0.01). The data indicate that elevation of plasma insulin to high physiological concentrations restrains FFA-induced ketogenesis.

Blood Glucose↗
PubMed1988

Effect of systemic pH on pHi and lactic acid generation in exhaustive forearm exercise.

To investigate whether changes in systemic pH affect intracellular pH (pHi), energy-rich phosphates, and lactic acid generation in muscle, eight normal volunteers performed exhaustive forearm exercise with arterial blood flow occluded for 2 min on three occasions. Subjects ingested 4 mmol/kg NH4Cl (acidosis; A) or NaHCO3 (alkalosis; B) or nothing (control; C) 3 h before the exercise. Muscle pHi and phosphocreatine (PCr) content were measured with 31P-nuclear magnetic resonance (31P-NMR) spectroscopy during exercise and recovery. Lactate output during 0.5-7 min of recovery was calculated as deep venous-arterial concentration differences times forearm blood flow. Before exercise, blood pH and bicarbonate were lower in acidosis (7.303 +/- 0.009, 18.6 +/- 0.5 meq/l) than alkalosis (7.457 +/- 0.010, 32.2 +/- 0.7 meq/l) and intermediate in control (7.389 +/- 0.007, 25.3 +/- 0.6 meq/l). Lactic acid output during recovery was less with A (245 +/- 39 mumol/100 ml) than B (340 +/- 55 mumol/100 ml) (P less than 0.05) and intermediate in C (293 +/- 31 mumol/100 ml). PCr utilization and resynthesis were not affected by extracellular pH changes. pHi did not differ before exercise (A, 7.04 +/- 0.01; B, 7.09 +/- 0.01; C, 7.06 +/- 0.01) or at its end (A, 6.28 +/- 0.07; B, 6.28 +/- 0.11; C, 6.31 +/- 0.09). Hence systemic acidosis inhibited and alkalosis stimulated lactic acid output. These findings suggest that systemic pH regulates cellular acid production, protecting muscle pH, at the expense of energy availability.

Adult↗
PubMed1988

Alterations in insulin clearance and hepatic blood flow during the night do not contribute to the 'dawn phenomenon' in type 1 diabetes.

To assess mechanisms leading to the 'dawn phenomenon' in type 1 diabetes mellitus, overnight insulin clearance, hepatic blood flow and insulin sensitivity of glucose metabolism were determined in 9 type 1 diabetic subjects treated with continuous subcutaneous insulin infusions. Glucose clamp studies were performed twice, once after midnight (from 24.00 to 02.00 h), and once in the early morning (from 06.00 to 08.00 h) during insulin infusion at 15 mU/m2/min. Insulin clearance was 482 +/- 57 ml/m2/min during the first, and 528 +/- 56 ml/m2/min during the second clamp (nonsignificant). Hepatic plasma flow assessed by measuring indocyanine green clearance was 984 +/- 115 and 1,040 +/- 163 ml/min, after the first and after the second clamp, respectively (nonsignificant). Glucose uptake during the two clamps was not significantly different. Since hepatic blood flow is known to influence insulin clearance and hepatic glucose metabolism, the data demonstrate that overnight changes in hepatic blood flow and insulin clearance do not contribute to the previously described early morning increase in insulin requirements in type 1 diabetic subjects (dawn phenomenon).

Adult↗
PubMed1988

Destruction of ethidium bromide in solution by ozonolysis.

Ethidium bromide can be rapidly destroyed in aqueous solutions or in isoamyl alcohol by ozonolysis in the presence of H2O2 to give a mixture of organic acids. In a variety of buffers commonly used in recombinant DNA technology destruction of ethidium bromide was more than 99.9%. The yellow reaction mixture after ozonolysis was shown to be nonmutagenic. This method may be used in laboratories for the disposal of ethidium bromide wastes.

Chemical Phenomena↗
PubMed1988

Hormonal counterregulatory responses to human (semi-synthetic and recombinant DNA) and porcine insulin induced hypoglycaemia.

Controversy exists over differences in hormonal counterregulatory (CR) responses to human and porcine insulins with conflicting reports regarding the adrenaline, glucagon, growth hormone, cortisol and prolactin responses to the two species of insulin. It has been suggested that these differences may represent different central nervous system sensitivities to the two types of insulin. The CR responses to an intravenous bolus of 0.1 U/kg of neutral soluble semi-synthetic (SSHI) and biosynthetic (BHI) human insulins, porcine insulin and diluting medium as control were compared in six fasted normal male subjects. The plasma glucose fell similarly with all three insulins reaching a mean nadir of 1.5 +/- 0.2 mmol/l at 25 min. Peak responses to porcine, SSHI and BHI, respectively were: adrenaline--523 +/- 101, 424 +/- 62, 379 +/- 76 pg/ml; glucagon--0.064 +/- 0.01, 0.063 +/- 0.01, 0.078 +/- 0.01 nmol/l; cortisol--507 +/- 42, 539 +/- 65, 507 +/- 42 nmol; growth hormone--76 +/- 10, 76 +/- 5, 64 +/- 15 mU/l; prolactin--507 +/- 72, 608 +/- 103, 523 +/- 118 mU/l. These differences in CR response were not statistically significant. The results do not support the suggestion of a different hormonal counterregulatory response or central nervous system sensitivity to human and porcine insulins when administered by intravenous bolus injections to normal subjects.

Adult↗
PubMed1987

Alpha 1-adrenergic stimulation of ketogenesis and fatty acid oxidation is associated with inhibition of lipogenesis in rat hepatocytes.

The effect of norepinephrine on fatty acid synthesis (3H2O incorporation into fatty acids), on fatty acid oxidation to CO2 and on ketogenesis was studied in isolated hepatocytes of fed rats. After incubation with norepinephrine (50 microM), lipogenesis was lower (5.7 +/- 1.1 nmoles 3H2O incorporated into fatty acids/mg dry weight/30 min) than in controls (7.5 +/- 1.7; n = 6, p less than 0.02). In contrast, (1-14C) palmitate conversion into total ketone bodies was increased to 10.9 +/- 1.8 nmoles/mg/30 min with norepinephrine, vs 8.5 +/- 1.6 in controls (p less than 0.05), and more (1-14C) palmitate was converted to 14CO2 with norepinephrine than in controls (1.48 +/- 0.10 nmoles/mg/30 min vs 1.06 +/- 0.11, p less than 0.05). The inhibitory effect of norepinephrine on lipogenesis was abolished by addition of the alpha 1-receptor blocker prazosin, but not by alpha 2 or beta-blockers. The results demonstrate that the ketogenic effect of norepinephrine is coupled with an inhibitory effect on lipogenesis which may be explained by diminished activity of acetyl-CoA carboxylase, diminished formation of malonyl-CoA and decreased activity of carnitine palmitoyl transferase I.

Animals↗
PubMed1987

Actinomycin synthetases. Multifunctional enzymes responsible for the synthesis of the peptide chains of actinomycin.

Two enzymes were purified from actinomycin-synthesizing Streptomyces chrysomallus which could be identified as peptide synthetases involved in the biosynthesis of actinomycin. Actinomycin synthetase II activates the first two amino acids of the peptide chains of the peptide lactone antibiotic, threonine and valine (or isoleucine), as thioesters via their corresponding adenylates. It is a single polypeptide chain of Mr 225,000. Similarly, actinomycin synthetase III activates proline, glycine, and valine (the remaining three amino acids in the antibiotic) as thioesters and is a single polypeptide chain of about Mr 280,000. It also carries the methyltransferase function(s) for N-methylation of thioesterified glycine and valine. In addition, it catalyzes the formation of cyclo(sarcosyl-N-methyl-L-valine) from glycine, L-valine, and S-adenosyl-L-methionine at the expense of ATP. Although the cell-free synthesis of the peptide lactone was not as yet accomplished, the data provide evidence that together with the 4-methyl-3-hydroxyanthranilic acid-activating enzyme (now designated as actinomycin synthetase I) all amino acid-activating protein components of the actinomycin-synthesizing enzyme complex are identified.

Amino Acids↗
PubMed1987

[C-peptide determination in diabetics for the evaluation of insulin requirements].

45 non-insulin dependent diabetic subjects with "secondary failure" of oral treatment were observed for 2 years; during this period 23 of the 45 became insulin requiring. Plasma C-peptide concentrations at study entry and several clinical parameters of the patients were analysed statistically using discriminant analysis to test their value in predicting the need for later insulin therapy. The results demonstrated the fasting C-peptide concentrations and, independently of this, the simultaneously measured glucose level had a significant predictive power, e.g. only patients with fasting glycemia of greater than 12 mmol/l and C-peptide concentrations exceeding 700 pmol/l did not require insulin during follow-up. Increased C-peptide concentrations pointed to a predominance of insulin resistance which correlated with an increased chance of being treatable without insulin. A further group of 44 elderly, insulin-treated diabetic subjects were examined for clinical markers of type 1 and type 2 diabetes when these patients were separated into type 1 and 2 diabetes according to their fasting C-peptide concentrations. It was demonstrated that age, weight and duration of diabetes did not significantly differ between the 2 types of diabetes in this group of patients. The studies demonstrate that determination of plasma C-peptide concentration is a valuable tool in distinguishing the two types of diabetes (type 1 and type 2). This distinction has clinical implications with regard to genetic counselling or the search for other endocrinopathies. In addition, fasting C-peptide measurement is a valuable tool, in conjunction with blood sugar determination, in deciding whether patients with secondary failure of oral antidiabetic treatment require long-term insulin therapy.

Adult↗
PubMed1987

Circulating somatostatin. Physiological regulator of pancreatic function?

The present study was designed to determine whether somatostatin is released into the circulation in sufficient amounts to regulate exocrine and endocrine pancreatic function and to evaluate the possible role of somatostatin as a hormonal regulator of the pancreas. Mean plasma somatostatin levels (SLI) increased from 11 +/- 2 pmol liter-1 to peak concentrations of 18 +/- 2 in six healthy male volunteers after a steak meal (P less than 0.05). Infusion of somatostatin inhibited hormone-induced exocrine pancreatic secretion and suppressed cerulein-stimulated pancreatic polypeptide (PP) secretion, but did not significantly change arginine-stimulated insulin and glucagon release at mean plasma somatostatin concentrations within the range seen after a meal. The amount of somatostatin released after a meal thus was of sufficient magnitude to inhibit exocrine pancreatic function and PP release. On the other hand, basal and arginine-stimulated glucagon and insulin secretions were not significantly affected by these plasma concentrations of intravenous somatostatin suggesting that the exocrine pancreas might be more sensitive to somatostatin than the islet cells. We conclude that somatostatin in concentrations within the range seen after a meal is a potent inhibitor of stimulated acinar cell function in man. The findings support the hypothesis that somatostatin acts as a true hormonal regulator.

Adult↗