Hormone content of mouse pancreatic islets subjected to different in vivo and in vitro functional demands

Summary Mice treated for 4 days with tolbutamide displayed decreased serum glucose values with a concomitant decrease of their islet insulin content. Mouse islets cultured for 1 week at a low (3 mM) or a high (28 mM) glucose concentration contained less insulin than non-cultured islets and islets cultured at a medium (11 mM) glucose concentration. All groups of cultured islets contained more glucagon than non-cultured islets. The somatostatin content of high- and medium-glucose cultured islets was higher than that of freshly isolated islets.The skilled technical assistance of Astrid Nordin, Ewa Forsbeck and Eva Törnelius is gratefully acknowledged. Financial support was received from the Swedish Medical Research Council (12X-109; 12X-2297), the Nordic Insulin Fund and the Swedish Diabetes Association.     

Cysteine-induced effect on amino acids in neonatal rat brain

Summary In neonatal rat brain 6 h after s.c. administration of L-cysteine, an increase was observed in most of the amino acids with the exception of glutamic acid, aspartic acid, phenylalanine, sarcosine, glutamine, hydroxyproline and phosphoethanolamine compared to age-matched saline controls. Cysteine was not present at detectable levels in control brain but was found to be 0.38 to 0.52 mole/g of fresh brain tissue in 2- and 4-day-old rats respectively after cysteine treatment.     

Effects of starvation and Ca++ on glucose-induced accumulation of cyclic 3',5'-AMP in pancreatic islets.

Exposure to glucose in the presence of 3-isobutyl-1-methylxanthine leads to accumulation of cAMP in islets microdissected from ob/ob mice. This process is dependent on extracellular Ca++ but differs markedly from the glucose action on insulin release in the same in vitro system in disappearing after 18 h of starvation.     

Changes in the free amino acids of the haemolymph of diapause and non-diapause pupae of the cotton bollworm,Heliothis armigera Hbn. (Lepidoptera: Noctuidae)

Summary The concentration of free amino acids in the haemolymph of non-diapausing and diapausing pupae ofHeliothis armigera was investigated. 20 amino acids were detected in the haemolymph of the studied stages. Asparagine, glutamine, cystine, ornithine, histidine and valine were the predominant free amino acids at all stages. The diapause resulted in increased levels of most of the amino acids.     

Involvement of D-amino acid oxidase in elimination of D-serine in mouse brain

The physiological role of D-amino acid oxidase (EC 1. 4. 3. 3) in mouse brain is described. The presence of D-enantiomers of neutral common amino acids was surveyed in the brain. D-serine was shown to be present at high concentration only in regions where the enzyme activity was low. In normal mice whose D-amino acid oxidase activity was much higher in the cerebellum than in the cerebrum, free D-serine content was apparently lower in the cerebellum than in the cerebrum. In mice of a mutant strain lacking D-amino acid-oxidase activity, the free D-serine level was remarkably high both in the cerebrum and cerebellum. The results suggest that the enzyme is involved in the elimination of free D-serine in the cerebellum.     

Gesteigerte Saugfrequenz vonDactynotus jaceae L. (Homoptera,Aphididae) bei Erhöhung des Aminosäurengehaltes in der Wirtspflanze

Summary In isolated shoots ofCentaurea jacea, placed in a solution of 0.5% glutamic acid for 15 h, the concentration of free amino acids in the stems is more than doubled. Compared with the controls, these shoots with an increased amino acid concentration are preferred by aphids in the preference-test.     

Involvement of D-amino acid oxidase in elimination of D-serine in mouse brain.

The physiological role of D-amino acid oxidase (EC 1. 4. 3. 3) in mouse brain is described. The presence of D-enantiomers of neutral common amino acids was surveyed in the brain. D-serine was shown to be present at high concentration only in regions where the enzyme activity was low. In normal mice whose D-amino acid oxidase activity was much higher in the cerebellum than in the cerebrum, free D-serine content was apparently lower in the cerebellum than in the cerebrum. In mice of a mutant strain lacking D-amino acid-oxidase activity, the free D-serine level was remarkably high both in the cerebrum and cerebellum. The results suggest that the enzyme is involved in the elimination of free D-serine in the cerebellum.     

Effects of starvation and Ca++ on glucose-induced accumulation of cyclic 3′,5′-AMP in pancreatic islets

Summary Exposure to glucose in the presence of 3-isobutyl-1-methylxanthine leads to accumulation of cAMP in islets microdissected fromob/ob-mice. This process is dependent on extracellular Ca⁺⁺ but differs markedly from the glucose action on insulin release in the same in vitro system in disappearing after 18 h of starvation.Supported by the Swedish Medical Research Council (No. 12x562).     

Role of protein kinase C and Ca2+ in glucose-induced sensitization/desensitization of insulin secretion.

The role of protein kinase C and Ca2+ in glucose-induced sensitization/desensitization of insulin secretion was studied. A 22-24 h exposure of mouse pancreatic islets to glucose (16.7 mmol/l) in TCM 199 culture medium, with 0.26 mmol/l or 1.26 mmol/l Ca2+, reduced total islet protein kinase C activity to approx. 85% and 60% of control values, respectively. At 0.26 mmol/l Ca2+ in TCM 199 medium, exposure to glucose (16.7 mmol/l) led to a potentiation of both phase 1 and phase 2 of glucose-induced insulin secretion, and caused a shift in the dose-response curve with 10 mmol/l and 16.7 mmol/l glucose exhibiting equipotent effects in stimulation of insulin secretion. In glucose-sensitized islets, the phorbol ester 12-O-tetradecanoylphorbol 13-acetate (0.16 mumol/l) did not further potentiate induction of secretion by 10 mmol/l or 16.7 mmol/l glucose. At 3.3 mmol/l glucose, however, phorbol ester-induced secretion was augmented, and was characterized by a faster onset of secretion in glucose-sensitized islets relative to control islets. In contrast, a partial reduction in arachidonic acid (100 mumol/l)-induced insulin release was observed in glucose-sensitized islets in the absence of extracellular Ca2+. Increasing the Ca2+ concentration to 1.26 mmol/l in TCM 199 during the 22-24 h exposure to glucose (16.7 mmol/l) led to inhibition of phase 1 and abolition of phase 2 of glucose (10 mmol/l, 16.7 mmol/l)-induced insulin secretion. In addition, this treatment abolished phorbol ester-induced and arachidonic acid-induced insulin secretion at 3.3 mmol/l glucose. Altogether, these data suggest that sensitization of insulin secretion is caused by a preferential down-regulation of the inhibitory effects of protein kinase C, leading to an increased first phase, and an increased coupling of glucose to the stimulatory effects of protein kinase C during the second phase of glucose-induced insulin secretion. Desensitization of insulin secretion appears to be a consequence of sustained Ca2+ influx, inducing extensive down-regulation of protein kinase C and also causing deleterious effects on islet cell function in protein kinase C-deprived islets.     

Keto acids and free amino acids during leaf growth in Bauhinia purpurea L

Summary The biosynthesis of keto acids and free amino acids was studied during the growth of Bauhinia purpurea leaves. -KGA, OAA, pyruvic acid and PEP are the important keto acids observed at various stages. The first 2 metabolites show a progressive increase and PEP OAA pathway is very active during the process of growth.     

Effect of various factors on the activity of trehalase from the larvae of Sesamia inferens Walker (Insect).

Trehalase from the salivary glands and the midgut of Sesamia inferens showed optimum activity at pH 5.8, and at temperatures of 50 and 60 degrees C respectively. The increase in the incubation period, enzyme concentration, and substrate concentration respectively increased the end-product, the hydrolysis, and the rate of hydrolysis of the substrate. Dialysis did not affect, tryptophan accelerated, and other amino acids and end-product inhibited the enzyme activity.     

Free amino acids in some tissues of marine crustacea

Summary Free amino acids contained in extracts of crustaceans were separated and determined quantitatively by ion exchange chromatography. In the hepatoprancreas of the brachyuran crustaceanCarcinus maenas, glycine, arginine, proline and alanine constituted 78.7% of the total amino acid pool. InEriphia spinifrons andMaja verrucosa, glycine, alanine, lysine and leucine comprised 54.9–66.9% of the total content. In the muscle tissue of the macruran crustaceaPalaemon, glycine, arginine, proline and alanine were the most common free amino acids and comprised 70–95% of the total content. The high concentrations of some amino acids in tissues of crustaceans may play a role in intracellular osmotic regulation and also in the maintenance of ionic hydrogen concentration.Acknowledgments. The author wishes to thank Mr R. Mari for his skillful help in the amino acid analyses and Miss G. Princivalli for typing the mansucript.     

The plasma level of some amino acids and physical and mental fatigue

Tryptophan is converted to 5-hydroxytryptamine (5-HT) in the brain and evidence is presented that an increase in the concentration of 5-HT can result in physical and mental fatigue during prolonged exercise. The entry of tryptophan in the brain is influenced by the plasma level of free tryptophan (that not bound to albumin) and, from competition for entry into brain, by the plasma level of branched chain amino acids. Hence, oral administration of branched chain amino acids could, theoretically, prevent the increase in 5-HT level during exercise and therefore delay physical and mental fatigue. Evidence in support of this hypothesis is presented.     

Ethanol influence on insulin secretion from isolated rat islets

Summary This study was done to delineate the role of - and -adrenergic receptors and cyclic AMP in the mechanism of ethanol effects on insulin release from isolated islets. Rats were given an -adrenergic blocker, phentolamine, or a -adrenergic blocker, propranolol. In addition, ethanol 1 g/kg was given intragastrically 1 h prior to sacrifice. Glucose mediated insulin release from isolated islets was enhanced by phentolamine and decreased by propranolol. Ethanol treatment inhibited glucose-induced insulin release from isolated islets of control rats as well as those given phentolamine and/or propranolol. Insulin release from isolated islets in response to dibutyryl-cyclic AMP was attenuated by ethanol. Theophylline enhanced glucose mediated insulin release from control islets but ethanol treatment produced a significant inhibition of insulin response. The data suggest that the site of action of the deleterious effects of ethanol on insulin release from isolated islets in rat does not involve adrenergic system and cyclic AMP.Supported by the U.S. Veterans Administration     

Conformational constraints on side chains in protein residues increase their information content

Like all other complex biological systems, proteins exhibit properties not seen in free amino acids (i.e., emergent properties). The present investigation arose from the deduction that proteins should offer a good model to approach the reverse phenomenon, namely top-down constraints experienced by protein residues compared to free amino acids. The crystalline structure of profilin Ib, a contractile protein of Acanthamoeba castellanii, was chosen as the object of study and submitted to 2-ns molecular dynamics simulation. The results revealed strong conformational constraints on the side chain of residues compared to the respective free amino acids. A Shannon entropy (SE) analysis of the conformational behavior of the side chains showed in most cases a strong decrease in the SE of the 1 and 2 dihedral angles compared to free amino acids. This is equivalent to stating that conformational constraints on the side chain of residues increase their information content and hence recognition specificity compared to free amino acids. In other words, the vastly increased information content of a protein relative to its free monomers is embedded not only in the tertiary structure of the backbone, but also in the conformational behavior of the side chains. The postulated implication is that both backbone and side chains, by virtue of being conformationally constrained, contribute to the recognition specificity of the protein toward other macromolecules and ligands.Received 13 July 2003; received after revision 18 August 2003; accepted 4 September 2003     

Free amino acid composition of the intestinal contents,intestinal cells and hemolymph ofPhilosamia cynthia larvae

Summary Free amino acid composition of the intestinal contents, intestinal cells and hemolymph has been determined in larvae of the mothPhilosamia cynthia. From the hemolymph/lumen concentration ratio, an active transport could be inferred for neutral and basic amino acids. The values of cell/lumen and hemolymph/cell ratios suggested that the active step in the transport mechanism could be localized at the luminal pole of the enterocyte for neutral amino acids (except aromatic amino acids) and at the basolateral pole of the enterocyte for basic amino acids (except arginine).This work was supported by grants from Italian Consiglio Nazionale delle Ricerche and from Ministero della Pubblica Istruzione, Rome. The authors are indebted to Prof. V. Capraro for helpful discussion.     

The reversal of glucose repressed prodigiosin production inSerratia marcescens by the cyclic 3′5′-adenosine monophosphate inhibitor theophylline

Summary Glucose was found to cause severe repression of prodigiosin production inSerratia marcescens and a dose related partial reversal was demonstrated by theophylline. It is suggested that this reversal is due to the inhibition of cAMP phosphodiesterase and the concomitant increase in cellular cAMP concentration.     

Effects of several preoperative medications on fat cell lipolysis,and activity of adipose tissue cyclic AMP phosphodiesterase

Summary Effects were examined of atropine, diazepam, pethidene, promethazine, scopolamine, omnopon and papaverine on basal and noradrenaline-stimulated lipolysis in rat isolated fat cells and on rat adipose tissue cyclic AMP phosphodiesterase activity. Papaverine at high concentration (1 mM) inhibited both basal and hormone-stimulated lipolysis, whereas diazepam enhanced basal lipolysis. At a clinical dose, omnopon increased both basal and noradrenaline-stimulated lipolysis. Adipose tissue cAMP phosphodiesterase activity was strongly inhibited by 1 mM diazepam, papaverine, promethazine and omnopon (280 g ml^–1). Lack of enhancement of lipolysis by the established cAMP phosphodiesterase antagonist papaverine, is compartible with simultaneous inhibition also of adipose adenyl cyclase. Diazepam-stimulated lipolysis is compatible with its phosphodiesterase inhibitory activity. It is proposed that papaverine-containing omnopon may offer some survival advantages during surgical stress by facilitating a caloric supply.The authours are grateful to Dr D. C. Williams for his continued support and encouragement.     

Effects of pregnancy on the glucose-induced insulin release from cultivated pancreatic islets of the rat

Summary 7-day-cultured islets from pregnant Wistar rats released at 5.6 mM glucose significantly more insulin than islets from nonpregnant rats, whereas in vivo this heigthened glucose sensitivity is lost 48 h post partum.Investigations carried out as a part of the Forschungsprojekt Diabetes mellitus und Fettstoffwechselstörungen supported by the Ministry of Health of German Democratic Republic.     

Nutritional requirements of aeromonads and their multiplication in drinking water

Aeromonads can utilize a wide range of low molecular-weight compounds, including amino acids, carbohydrates and long-chain fatty acids at a concentration of a few micrograms per liter. Utilization of biopolymers such as gelatin, casein and amylose is slow at this concentration level. The concentration of substrates available for an A. hydrophila strain in drinking water was usually below 10 micrograms of C/l. The autochthonous bacteria utilized these substrates more rapidly than the aeromonads. The multiplication of aeromonads in drinking water during distribution is therefore explained by their growth on biomass components in the biofilm and in sediments in the pipes.