The induction of chromosomal damage in rat hepatocytes and lymphocytes II. Alkylation damage and repair of rat-liver DNA after diethylnitrosamine,dimethylnitrosamine and ethyl methanesulphonate in relation to clastogenic effects

Rat-liver DNA alkylation by diethylnitrosamine (DEN), dimethylnitrosamine (DMN) and ethyl methanesulphonate (EMS) was studied in an attempt to relate chromosome-damaging effects of these agents (the formation of micronuclei in hepatocytes; see preceding paper) to specific alkylation patterns. No correlation was observed between the induction of micronuclei and liver DNA N-alkylation, measured as 3- and 7-alkyl-purines. O⁶-Alkylguanine is probably not involved in micronucleus induction because it is lost from DNA too rapidly to explain the much more persistent clastogenic effects. In contrast, both the initial amounts of alkylphosphotriesters and the persistencies of these products roughly paralleled the respective effects on micronucleus induction. The possible involvement of alkylphosphotriesters or other O-alkylation products of comparable stabilities is discussed. Results with DMN suggest that part of the primary DNA methylation damage is converted into a secondary (DNA) lesion and that both the primary and secondary lesion(s) contribute to the process of micronucleus formation.     

The Importance of Hydrodynamics for Protected and Endangered Biodiversity of Lowland Rivers

This paper examines the relationship between protected and endangered riverine species (target species) and hydrodynamics in river-floodplain ecosystems, combining ecological and policy-legal aspects of biodiversity conservation in river management. The importance of different hydrodynamic conditions along a lateral gradient was quantified for various taxonomic groups. Our results show that (i) target species require ecotopes along the entire hydrodynamic gradient; (ii) different parts of the hydrodynamic gradient are important to different species, belonging to different taxonomic groups; (iii) in particular low-dynamic parts are important for many species and (iv) species differ in their specificity for hydrodynamic conditions. Many species of higher plants, fish and butterflies have a narrow range for hydrodynamics and many species of birds and mammals use ecotopes along the entire gradient. Even when focussing only on target species, the entire natural hydrodynamic gradient is important. This means that the riverine species assemblage as a whole can benefit from measures focussing on target species only. River reconstruction and management should aim at re-establishing the entire hydrodynamic gradient, increasing the spatial heterogeneity of hydrodynamic conditions.     

A Mesoscale Model of DNA and Its Renaturation

A mesoscale model of DNA is presented (3SPN.1), extending the scheme previously developed by our group. Each nucleotide is mapped onto three interaction sites. Solvent is accounted for implicitly through a medium-effective dielectric constant and electrostatic interactions are treated at the level of Debye-Hückel theory. The force field includes a weak, solvent-induced attraction, which helps mediate the renaturation of DNA. Model parameterization is accomplished through replica exchange molecular dynamics simulations of short oligonucleotide sequences over a range of composition and chain length. The model describes the melting temperature of DNA as a function of composition as well as ionic strength, and is consistent with heat capacity profiles from experiments. The dependence of persistence length on ionic strength is also captured by the force field. The proposed model is used to examine the renaturation of DNA. It is found that a typical renaturation event occurs through a nucleation step, whereby an interplay between repulsive electrostatic interactions and colloidal-like attractions allows the system to undergo a series of rearrangements before complete molecular reassociation occurs.     

Constituents of the essential oil of Lavandula latifolia

Thirty components were identified in Lavandula latifolia essential oil (spike oil). One of the compounds, espliegol (δ-terpineol), is a new natural product.     

Some meteorological conditions associated with forest fires in Galicia (Spain)

The present paper offers data on the effect of certain meteorological parameters on the outbreak of forest fires in Galicia (Spain). In a day-to-day analysis, the values of the stability of the air column and the saturation deficit at the lower levels are related to the number of fires occurring in the following 24 h.     

Maximal lactate steady state in rats submitted to swimming exercise.

The higher concentration during exercise at which lactate entry in blood equals its removal is known as 'maximal lactate steady state' (MLSS) and is considered an important indicator of endurance exercise capacity. The aim of the present study was to determine MLSS in rats during swimming exercise. Adult male Wistar rats, which were adapted to water for 3 weeks, were used. After this, the animals were separated at random into groups and submitted once a week to swimming sessions of 20 min, supporting loads of 5, 6, 7, 8, 9 or 10% of body wt. for 6 consecutive weeks. Blood lactate was determined every 5 min to find the MLSS. Sedentary animals presented MLSS with overloads of 5 and 6% at 5.5 mmol/l blood lactate. There was a significant (P<0.05) increase in blood lactate with the other loads. In another set of experiments, rats of the same strain, sex and age were submitted daily to 60 min of swimming with an 8% body wt. overload, 5 days/week, for 9 weeks. The rats were then submitted to a swimming session of 20 min with an 8% body wt. overload and blood lactate was determined before the beginning of the session and after 10 and 20 min of exercise. Sedentary rats submitted to the same acute exercise protocol were used as a control. Physical training did not alter the MLSS value (P<0.05) but shifted it to a higher exercise intensity (8% body wt. overload). Taken together these results indicate that MLSS measured in rats in the conditions of the present study was reproducible and seemed to be independent of the physical condition of the animals.