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Biomedical subjects

K Albert

Publications and source records attributed to K Albert.

At least 55 records · Page 3Linked to original sources
PubMed1993

Pattern formation in Hydra vulgaris is controlled by lithium-sensitive processes.

Application of lithium ions leads to dramatic alterations in the positional value and subsequently to the formation of ectopic foot or head structures in Hydra vulgaris. Prolonged LiCl treatment decreases and pulse treatment increases the positional value. The decrease in the positional value is manifested in the formation of multiple ectopic feet along the body axis of intact animals or regenerates. Regeneration experiments reveal that long term application of the ion leads to transformation of prospective head into foot tissue. This transformation requires lithium pretreatment and exposure of the excised pieces to lithium for a further 5-8 hr. Pulse treatment of hydra with lithium elevates the positional value. Regenerating distal thirds differentiate ectopic head structures instead of a foot. Changes in the lithium concentration during the experiment lead to the differentiation of ectopic heads in the upper as well as ectopic feet in the lower body region. The characteristics of pattern respecification presented in this paper suggest that lithium interferes with the main pattern forming system(s) in hydra.

Animals↗
PubMed1991

19F nuclear magnetic resonance spectroscopy of neuroleptics: the first in vivo pharmacokinetics of trifluoperazine in the rat brain and the first in vivo spectrum of fluphenazine in the human brain.

In vivo 19F nuclear magnetic resonance (19F-NMR) spectroscopy measurements of trifluorinated neuroleptics (fluphenazine--FL and trifluoperazine--TFP) were made in rat brain as well as in human brain. Animal studies were performed at 4.7 Tesla. Using rats that have been treated with FL over a period of 3 weeks, a NMR signal could be detected within 8-15 min. Following a single intravenous injection of TFP, brain levels could be monitored with a time resolution of 30 min. The first 19F-NMR examination of a patient was made at 3.0 Tesla 1 day after injection of FL decanoate (37.5 mg) in the course of which a signal could be detected within 30 min. It is expected that 19F-NMR will become an important tool in psychopharmacological research.

Adult↗
PubMed1991

Chemically bonded phases for the reversed-phase high-performance liquid chromatographic separation of basic substances.

A chemically bonded phase with a peptide group (PB) for reversed-phase high-performance liquid chromatography (HPLC) is described. This packing was prepared by a two-stage modification of the surface of silica gel with mono- and trifunctional 3-aminopropylsilane and then with an appropriate derivative of a fatty acid. Packings prepared in this way were compared with standard C18 materials used in HPLC. Surface characteristics of the packings before and after chemical modification were determined by different physico-chemical methods, e.g., porosimetry, elemental analysis, 13C and 29Si cross-polarization magic angle spinning NMR and HPLC. Chromatographic properties of these packings were evaluated by comparison between log k' of one phase and log k' of a second phase for substances with different chemical natures. The PB packing was found to be especially useful for the separation of basic substances.

Amino Acid Sequence↗
PubMed1990

In vivo 19F nuclear magnetic resonance spectroscopy of trifluorinated neuroleptics in the rat.

In vivo 19F NMR measurements of trifluorinated neuroleptics in the rat brain were made using a 13 x 18 mm surface coil at 4.7 T. The signal of fluphenazine was obtained within 8-15 min from brains of living rats treated chronically with drug doses of 5-30 mg/kg. Following the intravenous injection of a single dose of trifluoperazine (30 mg/kg), brain levels could be monitored with a time resolution of 30 min. The data demonstrate the possibility of obtaining in vivo pharmacokinetics of fluorinated agents in the rat brain. 19F NMR is expected to become an important tool in neurochemical research.

Animals↗
PubMed1990

Use of NEXIS in a medical research library.

The NEXIS online system is used a great deal in business and law libraries, but has been virtually overlooked by medical librarians due to their perception of the system as expensive and difficult to search. The changing health care environment has placed new demands on medical searchers for just the type of legal, business, governmental, and news information found in the full-text files in NEXIS. Through the recent introduction of News Plus software, NEXIS can be searched as never before by those unaccustomed to full-text search techniques. Besides simplifying the search process, the new software has cost-saving features since search building and file selection are accomplished offline, and several activities may be done simultaneously. NEXIS via News Plus should be seriously considered as an addition to the repertoire of online systems accessed by medical librarians.

Cancer Care Facilities↗
PubMed1989

Continuous-flow 13C-filtered 1H NMR spectroscopy of ethanol metabolism in rat liver perfusate.

Using a 188.5-microliters continuous-flow dual probe 1H[13C] spin-echo difference spectra of rat liver perfusate were acquired. The conversion of [1-13C]ethanol to [1-13C]-acetaldehyde was readily monitored as a function of time. In combination with 1-1 water nonexcitation and WALTZ 13C decoupling, this method proved to be superior in sensitivity and selectivity to direct 1H or 13C detection.

Animals↗
PubMed1987

Generation of formaldehyde by N-demethylation of antipyrine. Detection of formaldehyde in bile by 13C-NMR spectroscopy.

The importance of NMR spectroscopy as a tool to investigate metabolic events in vitro and in vivo becomes more and more evident. Particularly 13C-NMR spectroscopy is able to deliver a wide range of information regarding the chemistry of xenobiotics in vivo. We studied the N-demethylation of N-methyl-13C-labelled antipyrine using an isolated perfused rat liver with a fluorocarbon suspension (FC 43) as oxygen carrier. Bile was collected in different fractions during the experiment. On the vascular side metabolite formation was monitored by continuous flow NMR spectroscopy. In bile the metabolic events were detected by standard NMR techniques. The bile spectra exhibit, among others, a signal at 84.2 ppm, indicating formaldehyde hydrate derived from the N-methyl group of antipyrine by an oxidative metabolic pathway. Neither formaldehyde hydrate nor other oxidation products could be detected in the vascular perfusate. The biliary excretion of considerable amounts of formaldehyde during the N-demethylation of antipyrine might have toxicological consequences for the intra- and extrahepatic bile ducts.

Animals↗
PubMed1986

Fluorinated psychopharmacological agents: noninvasive observation by fluorine-19 nuclear magnetic resonance.

Fluorinated psychopharmacological agents were measured with fluorine-19 nuclear magnetic resonance spectroscopy in the brain of intact rats that had been treated with fluphenazine. These in vivo experiments were compared to in vitro measurements of fluphenazine-treated rats. A high-field shift was observed in both in vivo and in vitro measurements. On the basis of the in vitro measurements, fluphenazine concentration in the brains of treated rats was estimated. Our observations demonstrate the feasibility of this technique for determining fluorinated neuroleptics in live mammals.

Animals↗
PubMed1985

Effect of Yoshida ascites tumour on the circulation in rats.

The circulation in anaesthetized rats with Yoshida ascites tumour was studied. Cardiac output was determined according to the reference flow method, while the distribution of cardiac output by labelled microspheres 15 mu in diameter. Arterial blood pressure decreased by 39 mm Hg and TPR by 23% at unaltered cardiac output. Blood flow of the brain and the coronaries increased by 39-43% while that of the kidney and the intestines decreased by 43 and 28%, respectively. The cardiac output fractions of the brain, the coronaries and the hepatic artery increased considerably, while that of the kidney decreased. The haematocrit decreased from 43 to 23%. It is assumed that part of the circulatory alterations (redistribution of cardiac output) were due to the anaemia and its consequences, while the others (arterial hypotension, lack of increase in cardiac output) should be regarded as an effect of a factor reaching the circulation from the cells of the ascites tumour.

Anemia↗
PubMed1984

Generic tolbutamide tablet dissolution: intralot and interlot variation.

Dissolution profiles for 62 lots of tolbutamide tablets from six manufacturers have been characterized using the USP paddle-stirrer apparatus. Results of paddle-stirrer dissolution for percent drug dissolved at 10, 20, and 30 min correlated well (r2 = 0.7444) with results from the USP rotating-basket test for 39 lots of tolbutamide. Interlot and intralot variability in tolbutamide dissolution was highly dependent on the manufacturer. For one product, the intralot range (for six paddle-stirred tablets) of percent drug dissolved after 30 min was 50-68% while the maximum interlot range for mean dissolution was 58-104%. One lot failed to meet both the rotating-basket and the paddle-stirrer dissolution specifications. Tablet response to aging at 60, 75, and 98% relative humidity over time was also highly manufacturer specific. The innovator's product repeatedly dissolved well when fresh or aged at all humidities. Dissolution from some generic tablets was dramatically depressed by humidity aging, even after only 3 d. Pretreatment of tablets with simulated gastric fluid modified the dissolution profile of one poorly dissolving lot of tablets. Results indicate that manufacturing quality control is highly variable among tolbutamide tablets.

Humidity↗
PubMed1984

Effect of erythrocyte transfusion on the circulation of Guérin carcinoma-bearing rats.

In Guérin carcinoma-bearing rats during tumour growth cardiac output and blood flow to several organs were increased whereas TPR, vascular resistance of some regions and haematocrit gradually decreased. In response to erythrocyte transfusion the anaemia of tumour-bearing rats was considerably improved or corrected, however, the parameters for systemic and regional circulation were only partially restored. We presume that the circulatory "hyperkinesis" of tumour-bearing rats is partly due to the anaemia but also an unknown factor must be considered. The blood perfusion of the Guérin carcinoma was not affected by the erythrocyte transfusion thus it is feasible that the tumour vasculature is maximally dilated even with a normal haematocrit of the host.

Anemia↗
PubMed1984

[Polarographic determination of noxiptilin hydrochloride in tablets].

A direct current polarographic method is proposed for the determination of noxiptiline hydrochloride (1) in tablets. Electrochemical reduction of 1 in HCl (0.1 mol X 1(-1) yields by a 4e process a product identified as 10, 11-dihydro-5H-dibenzo[a,d]cyclohepten-5-amine. The relative standard deviation of the determination is 0.66% within the 10(-4) mol X 1(-1) range. The limit of detection is about 5 X 10(-6) mol X 1(-1). Individual tablet contents varied between 95.6 and 104.7%, conforming to the requirements of the monograph "Content Uniformity" U.S.P. XX.

Dibenzocycloheptenes↗
PubMed1983

[Amphiphilic drugs. 2. Relation between colloidal properties and pharmaceutic-technological, pharmacokinetic and pharmacodynamic behavior].

The physicochemical properties of amphiphilic drugs may affect the technological, pharmacokinetic and pharmacodynamic behaviours. Micelle formation of a drug is of considerable importance for its solubility, stability, adsorption pattern, mixed micelle formation and influences thus its pharmaceutical availability. The biological availability is in many cases decreased by interactions of a surface active drug with other substances before absorption, by altered diffusion behaviour and distribution properties. Colloidal association may also result in an alteration of pharmacodynamic effects. These relations depend on the fact, that discrete hydrophobic an hydrophilic parts in a molecule are also prerequisites for micelle formation and receptor interactions. Furthermore the high membrane affinity of these drugs is responsible for some therapeutic and toxic effects.

Animals↗
PubMed1980

Effect of tourniquet-shock on the circulation of rats bearing Guerin carcinoma.

Blood pressure, cardiac output (Evans blue dilution) and its fractions (Sapirstein's indicator dilution technique), nutritive organ and tumour blood flow and circulatory resistance were studied under anaesthesia 1.5 hour post-release of both hind limbs constricted for 2.5 hours in rats bearing Guérin carcinoma. In tourniquet-shock the redistribution of cardiac output was essentially similar in normal and tumour bearing rats: e.g. skin and kidney fractions of cardiac output were diminished in both instances. In tumour bearing animals the circulatory resistance of tumour vasculature was more markedly enhanced than that of organ vessels, thus tumour fraction of cardiac output was decreased accordingly. It appears that the tumour might also contribute considerably to the development of a circulatory redistribution in shock.

Animals↗