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D Barthel

Publications and source records attributed to D Barthel.

9 recordsLinked to original sources
PubMed1990

Exclusion of poly(ethylene glycol) from liposome surfaces.

The electrophoretic mobility of vesicles is measured for concentrations of poly(ethylene glycol) from 0 wt.% to 10 wt.%. Mixtures of phosphatidylcholines and phosphatidic acid are used. The zeta potential calculated from the electrophoretic mobility and the viscosity of the suspension becomes more negative for all vesicles studied. Binding of poly(ethylene glycol) to the phospholipid surface by addition of the poly(oxyethylene)-containing surfactant C12E8 has the opposite effect and a decrease of the zeta potential is observed. Independent measurements of the surface potential of the vesicles in the presence of PEG by use of a positively charged spin probe and ESR spectroscopy and a fluorescent pH indicator and fluorescence spectroscopy show that actually the surface potential is not changed. A theory of the electrophoretic behaviour of vesicles in the presence of PEG is given which explains the contradiction between the two methods. It is assumed that the polymer is excluded from the vesicle surface (depletion layer) and that the viscosity near the surface is lower than the viscosity in the bulk phase. The thickness of the depletion layer is calculated from the experiments. The decrease of the zeta potential in the presence of poly(oxyethylene) chains linked to the vesicle surface results from the friction increase.

Calcium↗
PubMed1988

Interaction of electrically charged drug molecules with phospholipid membranes.

Model membranes (egg-yolk PC liposomes) were exposed to the cationic form of amphiphilic drugs. Microelectrophoresis was used to measure the change of the electrokinetic potential as a function of the drug concentration. By use of the Gouy-Chapman theory the surface potential and surface charge density were calculated. A theoretical model postulating a simple partition equilibrium of the charged drug molecules between the membrane and the aqueous phase in the vicinity of the membrane failed to describe the experimental results. Modification of the partition law by introducing a mechanism of saturation at high drug concentrations, however, resulted in concordance of model and experiment. Some parameters of the model can be used as a means of evaluating the efficiency of neuroactive drugs.

Alprenolol↗
PubMed1979

[Incidence of gestational diabetes and changes in insulin secretion of pregnant women (author's transl)].

The 50-g oGTT was applied to pregnant women suspected of having contracted diabetes. Carbohydrate tolerances were pathological in 23.6 per cent of all probands and in borderline vicinity in 17.9 per cent. The oral glucose tainting test thus worked according to expectation by revealing a relatiively high frequency of disorders of the carbohydrate tolerance. Yet, impaired insulin secretion was established rarely, with high response having been recorded from only seven per cent and delayed insulin secretion from 4.1 per cent. Low response was not found at all. No correlations were found to exist, by the 50-g oGTT, between disorders of the carbohydrate tolerance and insulin secretion. The groups involved differed but little with regard to their IRI mean value curves. Sugar excretion in urine was found to be increased with significance in response to pathological carbohydrate tolerance in early pregnancy and may be used as a complementary criterion for diagnosis.

Blood Glucose↗
PubMed1978

[Incidence of gestational diabetes as well as changes in insulin secretion during pregnancy. 1. Studies on pregnant women suspected of diabetes using the glucose infusion test (GIT)].

Based on the glucose infusion test, we find with 17.9 per cent of a group of anamnestically tainted pregnant women gestational diabetes, and with 5.7 per cent of this group a carbohydrate tolerance with disturbed boundaries. With probands having a carbohydrate tolerance with disturbed boundaries we find a significantly more frequent IRI-high-response. This coincidence of a carbohydrate tolerance in the border range and of an IRI-high-response might correspond to the early asymptomatic stage of diabetes. In the following stages, there will take place a depression of the early insulin phase with a pathological carbohydrate tolerance of the pregnant women in the sense of a gestational diabetes. With probands exhibiting a disturbed carbohydrate tolerance, a diminished depression of free fatty acids is found. The total lipid content and cholesterol are not essentially changed. With women suffering from gestational diabetes urinary sugar excretion is significantly higher than with probands showing a normal carbohydrate tolerance.

Adult↗