Influence of praziquantel and Ca2+ on the bilayer-isotropic-hexagonal transition of model membranes

Praziquantel induces a bilayer to isotropic transition in the absence of Ca2+ in a mixed phospholipid membrane consisting of phosphatidylethanolamine (PE) and phosphatidylserine (PS) at a molar ratio of 2:1 at 25 degrees C or 35 degrees C, irrespective of the lipid/drug molar ratio (10:1; 2:1). Addition of Ca2+ at different PS/Ca2+ molar ratios (4:1, 2:1 or 1:1) leads to a transition to a hexagonal (HII) state. With a phospholipid membrane of different composition (PE/PS molar ratio 4:1) praziquantel exerts quite different effects in the presence of Ca2+ (PS/Ca2+ molar ratio 1:1). An isotropic-signal appears together with a bilayer one at 25 degrees C, while a HII-signal can be detected at 35 degrees C. Thus, two separate phases coexist at this PE/PS molar ratio, while at a PE/PS molar ratio of 2:1, praziquantel and Ca2+ induce only a HII-signal. The results with these model membranes show that praziquantel and Ca2+ exert drastic influences on bilayer-isotropic-hexagonal transitions. The possibility that this drug might act in the schistosomal tegumental membranes in the same way is discussed.     

Ergonomic evaluation of three new principles for mono‐incision in laparoscopic surgery

Several instruments exist for performing a simple laparoscopic procedure through one trocar‐incision. However, all of these instruments have well‐known image‐related disadvantages. In order to solve these problems three principles have been developed for which a new device was designed. The functionality of this device was evaluated with regard to four parameters: duration of task completion, number of errors, image‐stability and preference by users.

Although the differences between the three principles were small, the tests clearly showed that the problems surgeons experienced before have been significantly diminished by the new device. Time measurements showed a preference for principles 1 and 2 (1: manual zoom camera in combination with a standard grasping device; 2: laparoscope with an angle of 45° in combination with a standard grasping device), the surgeons expressing preference for principle 2. Furthermore, the new trocar system is the first device for mono‐incision in which two standard instruments (currently available on the market) are used simultaneously without enlarging the incision. Finally, each surgeon can work with the new device using the principle he/she is preferring.     

Familial type of hypophyseal nanism. Apropos of 7 families in western Algeria

Eighteen pituitary dwarfs belonging to 7 different West Algerian families were studied. Eleven patients from 4 families presented isolated growth hormone deficiency, 7 patients from 3 families had multiple pituitary hormone deficiencies. Serum GH levels before and after standard pharmacological stimulations were below 2 ng/ml in all cases. Three of 10 hGH treated patients increased significantly their growth rate (8.5 +/- 0.5 cm/year) during the first year of treatment; growth was moderate (5.3 +/- 0.8 cm/year) in 3 patients and poor (4.5 cm/year) in 2 patients. In 2 cases the follow-up is insufficient.     

Ecotoxicity of Contaminated Suspended Solids for Filter Feeders (Daphnia magna)

It is generally assumed that the dissolved fraction of a toxic substance in surface water is mainly responsible for toxicity to aquatic organisms. However, toxic compounds are often adsorbed or chemically bound to suspended particles in the water column, depending upon the physico-chemical conditions. In the present study potential adverse effects to filter feeding organisms by metal contaminated particles were investigated. In our hypotheses the adsorbed metals might desorb in the gastrointestinal tract—due to different physico-chemical conditions—and exert toxic effects. Clay and sand particles, algae and organic material (peat) were artificially contaminated with cadmium and zinc. The contaminated materials were resuspended in standard conditions and toxicity was measured for the water flea Daphnia magna (mortality at 48 hours). As a reference, supernatant solutions were used containing the same concentration of dissolved metal as the suspensions. It was also established that the test concentrations of solid material (250 and 500 mg/l uncontaminated particles) did not cause any mortality within 48 hours. Daphnids are filter feeders: they filtrate large amounts of surrounding water, redrawing particles as a food source. Results strongly indicate that contaminated particles threaten the health of these particle-feeding organisms. Compared to the reference severe acute toxic effects were seen and cadmium accumulation was increased when contaminated solid material was present. Results were essentially the same for the different materials used in the experiments, except for sand contaminated with cadmium. This shows that mineral as well as organic materials can contribute to the particle bound toxicity. Different results were obtained when a static set up was used instead of a flow through set up, illustrating that the route of administration is important to make particles available and thus to evaluate their toxicity. Contaminated particles clearly have toxic potency, not only because they are a continuous source of dissolved xenobiotics, but also because the particle bound fraction can become available within the body of particle feeding organisms. This could lead to unexpected high tissue concentrations. More insight is needed to predict the bioavailability of adsorbed pollutants. Results of this study already indicate that suspended solids should be considered as a separate compartment in risk evaluation of chemicals, effluents or natural surface waters. Received: 21 September 1999/Accepted: 21 March 2000