Disposition kinetics of propranolol isomers in the perfused rat liver

The aim of this study was to define the determinants of the linear hepatic disposition kinetics of propranolol optical isomers using a perfused rat liver. Monensin was used to abolish the lysosomal proton gradient to allow an estimation of propranolol ion trapping by hepatic acidic vesicles. In vitro studies were used for independent estimates of microsomal binding and intrinsic clearance. Hepatic extraction and mean transit time were determined from outflow-concentration profiles using a nonparametric method. Kinetic parameters were derived from a physiologically based pharmacokinetic model. Modeling showed an approximate 34-fold decrease in ion trapping following monensin treatment. The observed model-derived ion trapping was similar to estimated theoretical values. No differences in ion-trapping values was found between R(+)- and S(-)- propranolol. Hepatic propranolol extraction was sensitive to changes in liver perfusate flow, permeability-surface area product, and intrinsic clearance. Ion trapping, microsomal and nonspecific binding, and distribution of unbound propranolol accounted for 47.4, 47.1, and 5.5% of the sequestration of propranolol in the liver, respectively. It is concluded that the physiologically more active S(-)- propranolol differs from the R(+)- isomer in higher permeability-surface area product, intrinsic clearance, and intracellular binding site values.

Spatial and temporal definition of Ochlerotatus camptorhynchus (Thomson) (Diptera : Culicidae) in the Gippsland Lakes system of eastern Victoria

The confirmed vector of Ross River virus, Ochlerotatus camptorhynchus (Thomson), is the dominant mosquito species inhabiting saline marshes in coastal Victoria. This paper re-examines previously published data on Oc. camptorhynchus, plus additional data collected since that time, and provides greater spatial and temporal definition of Oc. camptorhynchus numbers at seven sites across the Gippsland Lakes system of eastern Victoria. A total of 357 672 Oc. camptorhynchus was captured from 1188 trap-nights across the seven trap sites during trapping seasons from 1990 to 2001. The dominance of Oc. camptorhynchus across the seven sites averaged 75%, with significant differences in mean abundance of Oc. camptorhynchus found between all trap sites. Significant differences in monthly abundance of Oc. camptorhynchus were observed for Wellington Shire. Increase in populations of Oc. camptorhynchus was associated with increases in rainfall at all trap sites, higher minimum temperatures at two of the seven trap sites, and wind speed at one trap site. Prioritisation of mosquito control may be applied based on spatial and temporal factors according to the findings of this study.

Swash overtopping and sediment overwash on a truncated beach

New experimental laboratory data are presented on swash overtopping and sediment overwash on a truncated beach, approximating the conditions at the crest of a beach berm or inter-tidal ridge-runnel. The experiments provide a measure of the uprush sediment transport rate in the swash zone that is unaffected by the difficulties inherent in deploying instrumentation or sediment trapping techniques at laboratory scale. Overtopping flow volumes are compared with an analytical solution for swash flows as well as a simple numerical model, both of which are restricted to individual swash events. The analytical solution underestimates the overtopping volume by an order of magnitude while the model provides good overall agreement with the data and the reason for this difference is discussed. Modelled flow velocities are input to simple sediment transport formulae appropriate to the swash zone in order to predict the overwash sediment transport rates. Calculations performed with traditional expressions for the wave friction factor tend to underestimate the measured transport. Additional sediment transport calculations using standard total load equations are used to derive an optimum constant wave friction factor of f(w)=0.024. This is in good agreement with a broad range of published field and laboratory data. However, the influence of long waves and irregular wave run-up on the overtopping and overwash remains to be assessed. The good agreement between modelled and measured sediment transport rates suggests that the model provides accurate predictions of the uprush sediment transport rates in the swash zone, which has application in predicting the growth and height of beach berms. (c) 2005 Elsevier B.V. All rights reserved.