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Biomedical subjects

A Neagu

Publications and source records attributed to A Neagu.

9 recordsLinked to original sources
PubMed2001

On the Na+,K+ pump in fluctuating membrane potentials.

The present work investigates the usefulness of noise in the activity of the Na+,K+ pump. Random gating activity of the neighboring ion channels causes local fluctuations of the electric potential. They are modeled by a Markovian symmetric dichotomic noise, added to the membrane potential. The noise-averaged pump current is calculated for a general rectangular voltage signal and the model parameters of the effective two-state enzyme cycle are tuned to fit experimental results. Then, using these parameters, the amount of transported charge is calculated, and studied as a function of noise intensity. Signal and noise characteristics are identified at which fluctuations enhance pump activity. The biological impact of this phenomenon seems to be absent in physiological conditions for it occurs at noise amplitudes over 50 mV, which are unlikely to appear due to ion channels. However, under some conditions, externally applied dichotomic noise of intensity about 150 mV may sensibly increase the quantity of transported charge.

Biophysical Phenomena↗
PubMed2001

Fluctuations and the Hofmeister effect.

The Hofmeister effect consists in changes of protein solubility triggered by neutral electrolyte cosolutes. Based on the assumption that salts cause stochastic fluctuations of the free energy barrier profiles, a kinetic theory of this phenomenon is proposed. An exponentially correlated noise, of amplitude proportional to the salt concentration, is added to each energy level, and the time-dependence of the mean protein concentration is calculated. It is found that the theory yields the well-known Setschenow equation if the noise correlation time is low in comparison to the aggregation time constant. Experimental data on salting-in agents are well fitted, whereas, in the case of salting-out cosolutes, two independent dichotomic fluctuations are needed to fit the data. This may result from the fact that, in both cases, the low-concentration regime is dominated by salting-in electrostatic contributions, whereas, at high salt concentrations, electron donor/acceptor interactions become important; these have opposite effects. The theory offers a novel way to metricate Hofmeister effects and also leads to thermodynamic quantities, which account for the influence of salts. The formalism may also be applied to describe kinetic phenomena in the presence of cosolutes.

Electrolytes↗
PubMedDate not supplied

Pharmacokinetics of progesterone in postmenopausal women: 1. Pharmacokinetics following intravaginal administration.

Progesterone was administered to postmenopausal women in a form of vaginal suppositories containing 100 and 200 mg active substance in Butyrum cacao (BC) and Massa estarinum (ME), a base with emulsifying properties. In the case of single doses, blood samples were taken at 2, 4, 6, 24, 48 and 72 h. Another group of patients received vaginal suppositories (100 mg progesterone) once a day for a 6 day period, with blood samples taken 12 h after each administration. The plasma levels of progesterone were evaluated by radioimmunoassay. The time of maximum concentration (tmax) was 4 h in most cases, and 6 h in the others. The plasma levels were not dose-proportional. Peak plasma concentrations were in the range of 10-15 ng/ml with a mean of 10.5 ng/ml for the 100 mg and 12 ng/ml for the 200 mg doses. The ratio of the mean area under the curve (AUC) for 200 mg and the mean AUC for the 100 mg dose was found to be 1.37. Replacing BC with ME resulted in the lowering of cmax and AUC, and an increase in tmax following a reducing in the rate and extent of adsorption. In the case of ME suppositories, the variability in AUC, cmax and tmax was greater compared to that observed with the BC suppositories. Elimination half-time was in the range of 9-10 h for BC and 14 h for ME suppositories. In vitro assessment of the release kinetics from a hydrophobic and an emulsion type base confirmed previous findings: the latter base assured better pharmaceutical availability. The repeated doses did not seem to produce an accumulation of progesterone in the plasma. On the contrary, a small decrease in plasma levels over time appeared during the 6 day period. Numerical analysis revealed an excellent goodness of fit for the in vivo experimental data via biexponential curves, i.e. a pseudomonocompartmental model.

Administration, Intravaginal↗
PubMedDate not supplied

Pharmacokinetics of progesterone in postmenopausal women: 2. Pharmacokinetics following percutaneous administration.

Progesterone was administered percutaneously to postmenopausal women in topical applications on the breast and chest areas in a hydrophilic (gel), lipophilic and an emulsion type base. Venous blood samples were taken 2, 4, 6, 24, 48 and 72 h following administration. The plasma levels were evaluated by radioimmunoassay. Time of maximum concentration (tmax) was, in all cases, in the neighborhood of 4 h. Mean peak plasma concentrations were: 1 ng/ml for the lipophilic, 1.24 ng/ml for the hydrophilic and 2.26 ng/ml for the emulsion type base. The areas under the curves (AUCs) were practically equivalent for the first two methods, but higher values were obtained for administration in the emulsion type base. The elimination was slow, with a half-time varying in the range of 3040 h for all three types of base, a value that was much higher than those obtained after administration of progesterone via vaginal suppositories. The AUCs were parallel with the peak plasma concentrations: almost 2-fold higher for emulsion than for the gel and lipophilic base. Fit for plasma levels using mono-, bi- and tricompartmental models furnished acceptable results only in the case of monocompartmental model, which raises a number of physiological and physico-chemical considerations. A 'pseudomonocompartmental' model was constructed to explain this 'anomaly'.

Administration, Cutaneous↗
PubMedDate not supplied

[Infection with species of the genus Bordetella in adults, a factor in maintaining morbidity for whooping cough. Serological studies].

A number of 1021 serological investigations were performed to identify agglutinating antibodies against B. pertussis and B. parapertussis in adults. The investigations were initiated to study the presence of agglutinins in serum, in response to a previous infection with Bordetella species. The serological tests revealed the presence of agglutinating antibodies at titres considered to be positive (> or = 1/320) in 136 (13.3%) sera. The results obtained suggest that pertussis is relatively frequent in adults, and must be considered as a factor of maintaining morbidity.

Adolescent↗