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Why Do Historical Beeswax Seals Become Brittle Over Time?

ABSTRACTMechanical properties of aged beeswax were studied by an indirect measurement, using hydrogenated beeswax as a model material. The adequacy of the model was evaluated by comparison of its chemical composition and thermal properties with those of samples of historical beeswax. It was found that the gradual decrease in content of unsaturated compounds in beeswax contributes significantly to changes of its mechanical properties. As a consequence, beeswax artefacts become increasingly prone to mechanical damage during natural ageing. Understanding the difference between mechanical properties of recent and historical beeswax is primarily important from the point of view of safe handling and storage of such artefacts. Besides, this knowledge could help conservation scientists, e. g. when preparing model samples for testing new conservation methods.

Динаміка родючості ґрунтів орних земель Гощанського району Рівненської області

Динаміка родючості ґрунтів орних земель Гощанського району Рівненської області

Differential effects of various trivalent and pentavalent organic and inorganic arsenic species on glucose metabolism in isolated kidney cells

We have compared the acute toxicities of the trivalent arsenic species arsenite, oxophenylarsine (PhAsO), 2-chlorovinyloxoarsine (ClvinAsO), methyloxoarsine (MeAsO), and of the pentavalent arsenic species arsenate, methyl- and phenyl-arsonic acid in rat kidney tubules (RKT) and Madin-Darby canine kidney (MDCK) cells. In RKT, PhAsO (1 μmol I−1, 60 min) almost completely (>90%) blocked gluconeogenesis without affecting cell viability as assessed by dye exclusion. In MDCK cells, PhAsO (2 μmol I−1) markedly inhibited glucose uptake (60% of controls) within 30 min, while cell viability, as assessed by formazan formation, was not affected within 180 min. MeAsO and CIvinAsO were similarly effective to PhAsO in both RKT and MDCK cells. Estimated IC50 values for the inhibition of gluconeogenesis were 0.55 (PhAsO), 0.69 (CIvinAsO) and 0.99 μmol I−1 (MeAsO) and for the inhibition of glucose uptake 1.23 (PhAsO). 2.62 (CIvinAsO) and 6.99 μmol I−1 (MeAsO). At longer storage times, aqueous solutions of MeAsO and of CIvinAsO, but not of PhAsO, gradually lost toxic activity in RKT and MDCK cells, especially at alkaline pH. Concomitantly, a gradual decrease in content as assessed by HPLC was detected. Roughly 10-fold higher concentrations of arsenite than of PhAsO were required for comparable effects on gluconeogenesis in RKT, whereas in MDCK cells about 100-fold higher concentrations were needed for similar inhibition of glucose uptake. Pentavalent arsenate and phenylarsonate were two orders of magnitude less effective than PhAsO in RKT, while methylarsonate had virtually no influence on gluconeogenic activity. In MDCK cells the pentavalent arsenic species showed effects only in the millimolar range. It is concluded (1) that different mechanisms are involved in the acute toxicity of oxoarsines and inorganic arsenic and (2) that PhAsO offers advantages as a model substance for mono-substituted trivalent arsenicals, because it is more stable and more readily detectable.

Gonadotropin production and release in female goldfish (Carassius auratus) after administration of pimozide and an LHRH analogue as studied by electron microscopy and radioimmunoassay

The effect of pimozide and an LHRH-analogue (LHRH-A) on gonadotropic cells of the goldfish pituitary gland were described qualitatively and quantitatively. A scale of four categories was devised to reflect various ultrastructural appearances of the cells. Experimental animals were divided into a control group, a group injected with LHRH-A alone, pimozide alone, and groups receiving these two substances in combination. Fish injected with the single substance were killed 12 h after injection while the groups receiving the combined treatments were killed at 4, 12 and 48 h. Serum levels of gonadotropin measured by radioimmunoassay were used to indicate whether an increase in hormone release had occurred. An immunocytochemical technique, the protein A-gold procedure, assured that the cells studied were gonadotropes. The control group showed variation in the profiles of gonadotropic cells. The single treatment groups showed some increase in secretory inclusions. At 4 h after injection the combined treatment caused a significant increase in hormone granules; at 12 and 48 h there was a gradual decrease in content of secretory products, and an increase in vacuolization. The results indicate that the combined pimozide and LHRH-A treatment stimulated gonadotropin production as well as release.