Methylisobutylxanthine blocks insulin antagonism of cAMP-stimulated glycogenolysis at a site distinct from phosphodiesterase. Evidence favoring an insulin-insensitive calcium release mechanism

The widely used phosphodiesterase inhibitor MIX (1-methyl 3-isobutyl xanthine) blocked insulin antagonism of cAMP-stimulated glycogenolysis in rat hepatocytes but other phosphodiesterase inhibitors including Ro 20-1724 had no effect. Dose-response curves for MIX potentiation of cAMP-stimulated glycogenolysis and for MIX inhibition of the effects of insulin on cAMP-stimulated glycogenolysis suggested that at higher concentrations (250 microM) MIX may act at a site other than phosphodiesterase inhibition. MIX, at 250 microM, attenuated the insulin antagonism of glucose release stimulated by 8-bromo-cAMP, an extremely poor substrate for phosphodiesterase; other phosphodiesterase inhibitors did not. The possibility that MIX acts as an adenosine antagonist interfering with a postulated role for adenosine in insulin action was examined using N6-phenylisopropyladenosine (PIA), an Ra adenosine receptor agonist which increases hepatic cAMP levels. MIX inhibited insulin antagonism of PIA-stimulated glycogenolysis under conditions where it did not act as an adenosine antagonist (MIX and Ro 20-1724 both increased the response to PIA equally). The effect of concanavalin A on cAMP-stimulated glycogenolysis was antagonized by MIX, suggesting a post-receptor site of action for MIX. MIX paradoxically increased lactate production in the presence of 8-bromo-cAMP, reminiscent of the reported actions of calcium mobilizing hormones on lactate formation in fed hepatocytes. Cytosolic free Ca2+, as measured in Quin 2-loaded cells, was increased by MIX. In cells depleted of calcium, MIX no longer blocked insulin antagonism of 8-bromo-cAMP-stimulated glucose release, suggesting that MIX may function through an insulin-insensitive release of calcium. MIX greatly potentiated the stimulation of glycogenolysis by phenylephrine but did not alter the response to vasopressin. The relationship of this effect of MIX to the mechanism of insulin action and the ability of insulin to antagonize only alpha-adrenergic responses and not those of vasopressin is discussed.     

Water retention and plasma and urine composition in toads (Bufo viridis Laur.) under burrowing conditions

Summary Osmoregulation in the terrestrial toad,Bufo viridis, was studied under burrowing conditions in the laboratory. The toads can live for over 3 months burrowed in soil containing 9–10% moisture, maintaining constant body volume due to a large increase in the plasma osmolality, contributed mainly by urea. Water content of the tissues remains constant. Relatively large volumes of urine are stored in the urinary bladder during water restriction. The osmolality of the urine does not exceed that of the plasma. Urea uptake across the skin was measured in vitro and was greatly elevated in skins from the burrowed toads. The increase in plasma osmolality enables greater water absorption from the soil under water restricted conditions while the water content of the tissues is maintained constant since cell membranes are highly permeable to urea. It is concluded that the urea accumulating ability and urea tolerance form the basis for both the terrestriality and salt adaptability of this and other amphibian species.     

Stereospecific binding of diastereomeric peptides to salmon sperm DNA.

Studies of the interaction specificities of L-lysyl-L-phenylalaninamide (1) and the diastereomeric dipeptide amide, L-lysyl-D-phenylalaninamide (2), with salmon sperm DNA reveal distinct differences in the binding site of the aromatic ring of the phenylalanine residue. The results of 1H nuclear magnetic resonance (NMR), spin-lattice relaxation rates, viscometric, and flow dichroism studies indicate the aromatic ring of 1 is "partially" inserted between base pairs of DNA whereas the aromatic ring of 2 points outward toward the solution. The terminal L-lysyl residue presumably interacts stereospecifically with DNA helix thus dictating the positioning of the aromatic ring of the C-terminal phenylalanine residue. In the accompanying paper (E. J. Gabbay et al. (1976), Biochemistry, following paper in this issue), the interaction of several oligopeptide amides (containing the N-terminal L-Lys-L-Phe residue) with DNA is examined. The results are found to be consistent with stereospecific binding of the terminal L-lysyl residue, and in addition, the evidence suggests that oligopeptides may bind to DNA via a modified single-stranded beta-sheet structure which is wrapped around the nucleic acid helix in a manner similar to that described by M. H. F. Wilkins (1956), Cold Spring Harbor Symp. Quant. Biol. 21, 75).     

X-Ray and stereochemical studies on xylan diacetate

By means of x-ray fiber diffraction, it has been found that xylan diacetate crystallizes with two chains or four residues in a monoclinic cell (space group P2₁): a = 7.64, b = 12.44, c (fiber axis) = 10.31 Å, and γ = 85°. Pairs of residues are related by a twofold screw axis in the c direction. Based on the observed fiber repeat and chain symmetry, the probable conformation of a pair of xylose diacetate residues joined via a β-1,4′ linkage has been obtained by energy minimization methods. The conformations corresponding to a threefold screw axis and a twofold screw axis along the chain have been compared and the reason why xylan diacetate assumes a twofold screw axis seems to be due to intermolecular packing effects rather than intramolecular non-bonded interactions.     

Developmental changes in the heterocellular epidermis of Pelobates syriacus integument.

Changes in characteristic components of the skin epidermis of the large tadpole of Pelobates syriacus were studied throughout its development. The fate of two specific cells in the skin epidermis was followed, from the young tadpole to the adult was studied. It was found that flask-shaped type cells in the tadpole epidermis which are PAS-positive, stain with peanut lectin (PNA). There is no detectable band 3 in the premetamorphosed stages, and mitochondria-rich cells are very rare. This pattern of staining changes completely upon metamorphosis: the PAS-positive cells, specific to the tadpole epidermis disappear, and the mitochondria-rich (MR) cells in the adult skin epithelium react with polyclonal anti-band 3 antibody. Western blot analysis showed the presence of a band 3-like protein of about 95 kDa, only in the adult epithelial extract, corroborating the immunocytochemical observations. The finding of the presence of band 3-like protein in the MR cells of Pelobates, is similar to the observations made in the skin of other amphibian species. On the other hand, the binding of peanut lectin to MR cells is species-specific, since it does not react with the MR cells in the skin epithelium of Pelobates syriacus.     

Social evaluation of municipal solid waste management systems from a life cycle perspective: a systematic literature review

Purpose

The social aspects of municipal solid waste management (MSWM) systems are underpinning their sustainability and effectiveness. The assessment of these systems from a life cycle perspective is widespread throughout environmental life cycle assessment (LCA), but few studies have used social life cycle assessment (S-LCA). The present study is an innovative review with the objective to analyse and describe the current level of development of S-LCA applications in MSWM, and to identify the main methodological challenges and best practices, aiming at recommending approaches to harmonise future S-LCA applications in MSWM.

Materials and methods

A systematic review of the literature found 36 relevant scientific articles. These were submitted to bibliometric and content analysis, which includes an analysis of how methodological aspects of the four phases of S-LCA were applied in comparison with best practice and existing guidelines.

Results and discussion

There was a predominance of case studies in developing countries (59%) and evaluation of the stages of collection/transportation, pre-processing (sorting) and landfilling (55%). There were more studies focusing on stakeholders, “workers” and “local communities” and in the impact subcategories “employment”, “working hours”, “health and safety/working conditions”, “community involvement/participation” and “health and safety/living conditions of community”. There was great variability in the application of the method (47% of the studies included methodological developments). However, the 39% based on UNEP guidelines were closer to a methodological consensus.

Conclusion

In general, studies need more detail and clarity in describing the methodological decisions used. Improvements are needed for issues that limit the S-LCA method, including the difficulties of covering the entire life cycle, relating impacts to the functional unit, standardizing impact assessment methods, addressing allocation and data quality issues and interpretation of results and their limitations. Improvements can be achieved by using participatory methods in the selection of categories, subcategories and impact indicators, as well as by clarifying the definition of a product system and detailing “cut-off criteria” of processes/organizations and the impact of these decisions on results.