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Biomedical subjects

D D Breimer

Publications and source records attributed to D D Breimer.

At least 19 recordsLinked to original sources
PubMed1995

High-density lipoprotein and cerebral endothelial cells in vitro: interactions and transport.

Primary cultures of bovine cerebral endothelial cells were used as an in vitro model for the blood-brain barrier to study the transport and interactions of high-density lipoprotein (HDL) across monolayers of these cells. Transport of 125I-apoE free HDL across a monolayer of bovine cerebral endothelial cells occurred in a linear fashion up to a concentration of 70 micrograms/mL, suggesting paracellular transport of HDL. Bovine cerebral endothelial cells possess a high affinity binding site for HDL with a mean dissociation constant (KD) of 10.8 +/- 2.6 micrograms/mL (N = 4). Maximal binding of apoE free HDL to cerebral endothelial cells proved to be temperature-dependent: at 4 degrees a Bmax value of 42 +/- 9.3 ng/mg cell protein was found, while at 37 degrees this value was 177 +/- 70.4 ng/mg cell protein. Cell association of 125I-HDL could be effectively displaced by HDL, not by low-density lipoprotein or acetylated low-density lipoprotein, and association was not coupled to degradation. The in vitro blood-brain barrier cell system possesses high affinity binding sites for HDL, which are probably not involved in the transport of HDL across cerebral endothelial cells.

Animals↗
PubMed1995

Eicosanoid production by rat cerebral endothelial cells: stimulation by lipopolysaccharide, interleukin-1 and interleukin-6.

The capacity of rat cerebral endothelial cells (RCEC) to form eicosanoids was determined after incubation with 14C-labelled arachidonic acid. Prostaglandin E2 (PGE2) was the main metabolite formed by RCEC and was responsible for 54% of the total amount of eicosanoids produced. In contrast, in primary cultures of rat aorta endothelial cells, 32% of the amount of prostaglandins was 6-keto-PGF1 alpha). RCEC treated with 50 ng/ml LPS for 24 h responded with an augmented PGE2 synthesis and 6-keto-PGF1 alpha of 3.4-fold and 2.2-fold, respectively. Cultures treated with IL-1 beta (50 ng/ml) for 3 h showed a stimulation of the release of PGE2 and 6-keto-PGF1 alpha of 2.5- and 4.5-fold, respectively, and 2.0-fold and 2.3-fold, respectively, after IL-6 (50 ng/ml) incubation for 3 h. PGE2 is the main eicosanoid formed by RCEC in response to inflammatory agents, suggesting an important role of the cerebral endothelial cells in the transduction of an inflammatory response in the central nervous system.

Animals↗
PubMed1995

A computer-based international 'thesis-line'?

Doctoral theses represent a largely inaccessible mine of useful information. There is no simple way of finding out whether someone in another institution has written a thesis that is relevant to your own work, or of reading it. Here, we describe how this situation could be remedied by making theses freely available and easy to search in an international 'Thesis-Line' accessible through the Internet.

Academic Dissertations as Topic↗
PubMed1995

The use of intracerebral microdialysis to determine changes in blood-brain barrier transport characteristics.

The aim of this study was to determine whether changes in the transport of drugs into the brain could be determined by in vivo intracerebral microdialysis. Atenolol was used as a model drug to determine blood-brain barrier (BBB) transport characteristics. In rats, unilateral opening of the blood-brain barrier was achieved by infusion of hyperosmolar mannitol (25%, w/v) into the left internal carotid artery. BBB transport, expressed as the ratio of the area under the curve (AUC) of atenolol in brain extracellular fluid over plasma, was three times higher for the mannitol treated hemisphere as compared with the contralateral brain or after infusion of saline, being (mean +/- SEM) 0.094 +/- 0.024 (n = 16), 0.029 +/- 0.007 (n = 12) and 0.030 +/- 0.009 (n = 12) respectively. Further evaluation of the data indicated that for experiments performed in the morning the mannitol infusion had little effect on the extent of transport of atenolol into the brain, while in the afternoon BBB transport was about 10-fold higher than in the contralateral and saline group. The mean "afternoon" ratios +/- SEM were 0.155 +/- 0.038 (n = 8), 0.012 +/- 0.003 (n = 6) and 0.018 +/- 0.006 (n = 6) respectively. It is concluded that intracerebral microdialysis is capable of revealing changes in BBB transport and regional and time-dependent differences in drug levels can be demonstrated with the use of this technique.

Animals↗
PubMed1995

Absorption enhancement of a hydrophilic model compound by verapamil after rectal administration to rats.

The use of verapamil as an absorption enhancer for the paracellular route in-vivo was studied using FITC-labelled dextran (molecular weight 4000) (FD-4) as a hydrophilic model compound for transport enhancement. The kinetics of FD-4 after intravenous doses of 1 or 10 mg could be described by a two-compartment model with a systemic clearance of approximately 2 mL min-1 and a terminal plasma half-life of approximately 36 min. Rectal administration to rats, performed as a rectal infusion of 10 mg FD-4 together with 7 mM verapamil, resulted in a 10-fold increase in the percentage of the dose absorbed over a 5-h period compared with the control and a 6-fold increase compared with a bolus administration, although the total amount absorbed remained relatively low (approx. 3% maximum). Large inter-animal variation in effect values were noted. The data indicate that although verapamil is able to enhance the absorption of hydrophilic compounds in-vivo, practical application of verapamil for this purpose doses not seem feasible.

Administration, Rectal↗
PubMed1995

The influence of dietary restriction on the metabolism of theophylline and antipyrine in the ageing female BN/BiRij rat.

The influence of ageing and dietary restriction (DR) on the in vivo activities of different P450 enzymes was studied longitudinally in female BN/BiRij rats. For this purpose, antipyrine (AP) and theophylline (TH) were used as substrates. The metabolic clearances of AP (CIm AP) and TH (CIm TH) were used as indicators for P450 enzyme activities in vivo. Therefore, we also included the assessment of the clearances of formation of three AP metabolites, i.e., 3-hydroxymethylantipyrine (CI-->HMA), 4-hydroxyantipyrine (CI-->OHA) and norantipyrine (CI-->NORA). Ninety, 50 and 10% survival times were prolonged significantly in DR rats. In control animals, the contribution to the metabolism of AP in the formation of HMA, OHA and NORA, expressed as percentage of the dose, decreased with ageing, indicating that other pathways compensate for this decrease. Only a significant decrease in the metabolism to OHA was observed in DR animals. CI-->HMA, CI-->OHA and CI-->NORA showed an age-related decrease in the control rats, whereas in the DR rats an age-related decrease was observed for CI-->HMA and CI-->OHA. The results of the present study suggest that the decrease in the activities of the P450 enzymes involved in the formation of HMA, OHA and NORA have a later onset in the DR rats. In conclusion, DR not only has a strong positive influence on the health and life span of the rats, but also results in a delayed onset of the decrease in activity of certain P450 enzymes.

Aging↗
PubMed1995

Pharmacokinetic-pharmacodynamic modelling of the cardiovascular effects of R- and S-N6-phenylisopropyladenosine in conscious normotensive rats.

Recently, the commercially available adenosine receptor agonist S-N6-phenylisopropyladenosine (S-PIA) has been demonstrated to be contaminated with the more potent R-diastereomer. The potency of S-PIA may therefore have been overestimated in previously published in vivo studies. Our objective was to determine the potency of both diastereomers in conscious normotensive rats by using an integrated pharmacokinetic-pharmacodynamic model. In a cross-over designed study, the animals received i.v. infusions of 177 micrograms/kg (0.51 mumol/kg) R-N6-phenylisopropyladenosine (R-PIA) and 4000 micrograms/kg (11.6 mumol/kg) S-PIA. The infusion of S-PIA corresponded to a simultaneous administration of 3823 micrograms/kg (11.1 mumol/kg) and 177 micrograms/kg (0.51 mumol/kg) of the S- and R-diastereomer, respectively. During the experiment, time courses of heart rate and blood pressure were recorded continuously. Serial arterial blood samples were collected and concentrations were determined by using a stereoselective high-performance liquid chromatography assay. After administration of R-PIA, the individual concentration-effect relationships could be quantified by the sigmoidal Emax model, yielding an EC50 value of 24 +/- 3 ng/ml for the reduction in heart rate (mean +/- S.E., n = 12). After administration of S-PIA, a similar EC50 value was obtained when heart rate was correlated to concentrations of R-PIA. Modelling of the concentration-effect data according to a competitive interaction model did not yield pharmacodynamic parameter estimates for S-PIA. In conclusion, the cardiovascular effects observed after infusion of S-PIA may be attributed entirely to the presence of R-PIA.

Animals↗
PubMed1994

Critical factors of intracerebral microdialysis as a technique to determine the pharmacokinetics of drugs in rat brain.

The purpose of this investigation was to determine the effect of experimental conditions on the concentrations of atenolol and acetaminophen in brain microdialysate, and to investigate the feasibility of performing repeated experiments within individual rats. Following intravenous bolus administration, reproducible concentration-time profiles were obtained in plasma and in brain dialysate. Based on corrections for in vitro recoveries of the intracerebral probe, the estimated ratio of the AUC in brain extracellular fluid (AUCbrain ECF) over the AUC in plasma (AUCplasma) +/- S.E.M. was 3.8 +/- 0.6% (n = 6) for atenolol and 18 +/- 2% (n = 6) for acetaminophen. Upon intracerebroventricular administration, interanimal differences in kinetics of acetaminophen in brain dialysate were observed while the concentrations of atenolol were below the detection limit of the assay. The influence of the use of isotonic versus hypotonic perfusate solutions on AUCbrain ECF values after intravenous bolus administration of both drugs was determined. Repeated experiments with the isotonic perfusate (24, 48 and 78 h post-surgery) resulted in AUCbrain ECF values with the ratio of 100: 98: 76% for acetaminophen and 100: 103: 98% for atenolol. Using a hypotonic perfusion solution the ratio of AUCbrain ECF values was 100: 154: 114% for acetaminophen and 100: 378: 427% for atenolol. A clear effect of the temperature of the hypotonic perfusate (24 vs 38 degrees C) on acetaminophen AUCbrain ECF values was revealed. The ratio of AUCbrain ECF values obtained at 24: 38 degrees C was 192: 100%.(ABSTRACT TRUNCATED AT 250 WORDS)

Acetaminophen↗
PubMed1994

Absorption enhancement of hydrophilic compounds by verapamil in Caco-2 cell monolayers.

Caco-2 monolayers were used to determine whether verapamil enhanced the transport of hydrophilic compounds across epithelial cells. Transepithelial electrical resistance (TEER) measurements, as an indicator of the opening of tight junctions, and transport experiments with fluorescein-Na (Flu) and FITC-dextran Mw 4000 (FD-4) were used to assess the effect. (+/-) Verapamil concentrations up to 3 x 10(-4) M increased TEER dose-dependently, whereas from concentrations of 7 x 10(-4) M onwards a dose-dependent drop was found. After removal of verapamil (< 10(-3) M) the effects on TEER were reversible within 30 min. A second administration of verapamil after different time intervals produced a much larger effect on TEER than the first administration. The separate R- and S-enantiomers did not reveal a difference in enantiomer effect. (+/-) Verapamil at 7 x 10(-4) M increased Flu transport about 13-fold and 26-fold after the first and second treatment in the same monolayers, respectively. Transport of FD-4 increased approximately 4-fold and 6-fold after the first and second treatment, respectively. Potential damaging effects were assessed by trypan blue exclusion (cell death) and cell detachment. No cell death occurred at verapamil concentrations of 8.5 x 10(-4) M or lower, whereas cell detachment did not occur within 1 hr at all concentrations used in these experiments. At later times detachment was observed at concentrations of 7 x 10(-4) M and higher. Confocal laser scanning microscopy showed that verapamil opens the paracellular route, thereby enhancing the permeability of hydrophilic compounds. However, relatively high concentrations are needed to achieve this effect and only a narrow concentration range can be used without cytotoxic effects, which limits the potential application of verapamil as an absorption enhancing agent.

Biological Transport↗
PubMed1994

Lymphocyte adhesion to brain capillary endothelial cells in vitro.

The presence and upregulation of adhesion molecules on bovine brain endothelial cells (BBEC) were investigated. Monolayers of BBEC were incubated with lipopolysaccharide (LPS), interleukin-1 beta (rhIL-1 beta), and interleukin-6 (rhIL-6) to simulate in vitro an inflammatory site in the cerebral capillaries. Adhesion of lymphocytes to BBEC increased 4.1-fold after stimulation of the endothelial cells for 4 h with 5 or 10 ng/ml LPS. Lymphocyte adhesion increased after incubation of the BBEC for 4 h with IL-1 and was increased 3.7-fold using 100 ng/ml IL-1. BBEC pre-incubated with IL-6 for 4 h also showed an increase in adhesion of lymphocytes, and cells pretreated with 100 ng/ml IL-6 showed a 3-fold increase in lymphocyte adherence. Specific monoclonal antibodies directed against CD11a, CD18, and VLA-4 were able to block adherence of lymphocytes to stimulated BBEC. These results indicate that the in vitro activation of BBEC may serve as a model for the study of inflammation of the blood-brain barrier.

Animals↗
PubMed1994

Quantification and visualization of the transport of octreotide, a somatostatin analogue, across monolayers of cerebrovascular endothelial cells.

Confocal laser scanning microscopy (CLSM) was used to quantify and visualize the transport of the octapeptide and somatostatin analogue, octreotide (SMS 201-995, Sandostatin), across monolayers of bovine cerebrovascular endothelial cells, an in vitro model of the blood-brain barrier. The concentrations of octreotide and its conjugates in the cell culture medium were determined by radioimmunoassay (RIA). Two fluorescent conjugates of octreotide (FITC- and NBD-octreotide) were used to obtain CLSM images. The peptides did not undergo significant degradation in the presence of brain endothelial cell monolayers. The transport rate of octreotide expressed as clearance (Cl) and endothelial permeability (Pe) did not depend on either the initial concentration (between 10 nM and 1 microM) or the site of administration (luminal or abluminal side of the monolayer), indicating the absence of saturable and/or asymmetrical transport mechanisms. The Pe of octreotide and that of the paracellular permeability marker fluorescein correlated well. Although the conjugates are more lipophilic than octreotide itself, they exhibited lower Cl and Pe, values probably because of their larger molecular size. On the CLSM images, FITC-octreotide was present only in the intercellular space, while the cells did not exhibit detectable fluorescence. Transport studies and CLSM images suggest that octreotide passes the endothelial monolayer primarily via the paracellular route without significant contribution of carrier-mediated transport.

4-Chloro-7-nitrobenzofurazan↗
PubMed1994

In vitro and in vivo transport of zidovudine (AZT) across the blood-brain barrier and the effect of transport inhibitors.

The transport of the antiviral nucleoside analogue zidovudine (3'-azido-3'-deoxythymidine; AZT) into the central nervous system (CNS) was characterized in vitro and in vivo. The in vitro model consisted of primary cultures of isolated bovine capillary endothelial cells. The transport rate of AZT across the monolayer, expressed as endothelial permeability P, was determined following luminal and abluminal administration. P did not differ between the two administration sites (luminal, 1.65 +/- 0.44 cm/min/10(3); abluminal, 1.63 +/- 0.28 cm/min/10(3)). The transport of AZT across the endothelial cell monolayer was found to be concentration independent in the range between 0.4 and 50 micrograms/mL. AZT transport was not affected by pretreatment of the cells with either metabolic inhibitors (DODG and DODG/NaN3) or probenecid. This suggests that AZT passes the monolayer mainly by passive diffusion. The in vivo transport of AZT across the blood-brain barrier and the blood-CSF barrier was studied in male Wistar rats after coadministration of potential inhibitors of active transport of AZT: probenecid (organic anion transport) and thymidine (nucleoside transport). Intracerebroventricular and intravenous coadministration of probenecid caused a significant (P < 0.001) increase in the CSF/plasma concentration ratio compared to the control phase, indicating that the organic anion carrier is involved in AZT transport from CSF to blood. Since there was no effect of probenecid on the transport of AZT in vitro, it is suggested that this carrier is located at the choroid plexus. Coadministration of thymidine did not affect the CSF/plasma concentration ratio, suggesting that a nucleoside carrier system is not involved in AZT transport into or out of the CNS.

Analysis of Variance↗
PubMed1994

Effects of intravenous temazepam. I. Saccadic eye movements and electroencephalogram after fast and slow infusion to pseudo steady state.

OBJECTIVE: To study the pharmacodynamic effects of intravenous temazepam after different infusion rates to pseudo steady-state concentrations. METHODS: This was a randomized, double-blind, placebo-controlled crossover study in an academic department of clinical pharmacology. Subjects were nine healthy volunteers. A computerized infusion pump was used to obtain target plasma concentrations of temazepam after 30 or 120 minutes and to maintain these levels for 2 hours. A vehicle infusion, similar to the 30-minute (fast) infusion was used as a placebo control. Infusion schedules were based on data obtained from individual subjects after infusion of 0.4 mg/kg temazepam in 30 minutes. Target plasma concentrations were chosen to induce subhypnotic effects and averaged (+/- SD) 597 +/- 123 ng/ml. Venous plasma concentrations of temazepam were measured by HPLC. Free fractions of temazepam were assessed at the start of the pseudo steady-state concentration intervals. Electroencephalogram alpha and beta amplitudes, saccadic peak velocity, and saccadic latency were used as pharmacodynamic parameters. RESULTS: The rate of change of plasma concentrations averaged 21 +/- 4 ng/ml.min-1 during fast infusion and 5 +/- 1 ng/ml.min-1 during slow infusion of temazepam. Average pseudo steady-state concentrations were 639 +/- 132 ng/ml after fast infusion and 629 +/- 133 ng/ml after slow infusion. At the onset of pseudo steady-state concentration intervals the average free fractions of temazepam were 44% (95% confidence interval, 19% to 61%) lower for slow than for fast infusions. Compared with the slow infusion, electroencephalogram beta amplitudes were significantly larger during the first 30 minutes of pseudo steady-state concentration after fast infusion of temazepam. No significant differences were found for the other parameters. There was a slight decline of temazepam effects during the pseudo steady-state concentration intervals for all parameters after the fast infusion and for saccadic peak velocity and saccadic latency after the slow infusion. CONCLUSIONS: The pharmacodynamic effects of intravenous temazepam may depend partly on the rate of administration. Differences in pharmacodynamic effects after fast and slow infusions could be caused by changes in protein binding over time.

Dose-Response Relationship, Drug↗
PubMed1994

Effects of intravenous temazepam. II. A study of the long-term reproducibility of pharmacokinetics, pharmacodynamics, and concentration-effect parameters.

OBJECTIVE: To evaluate the long-term reproducibility of pharmacokinetic, pharmacodynamic, and concentration-effect parameters after intravenous administration of temazepam. METHODS: Nine healthy volunteers were studied. Temazepam, 0.4 mg/kg, was infused intravenously for 30 minutes on two occasions 6 months apart. Venous plasma concentrations of temazepam were measured by HPLC in samples obtained between 0 and 24 hours. Pharmacodynamic effects were evaluated up to 8 hours for saccadic peak velocity and electroencephalogram (EEG) beta amplitudes. Subjects' state and trait anxiety were assessed by use of the Spielberger anxiety inventory. RESULTS: Significant correlations between occasions were found for area under the plasma concentration-time curve (AUC) values (r = 0.91; p < 0.01) but not for maximum concentration and half-life. Significant correlations were also found for area under the effect-time curve (AUEC) values of peak velocity (r = 0.88; p < 0.01) but not for peak velocity (r = 0.48; p > 0.05). Significant differences between the slopes of concentration effect plots on different occasions were observed in two subjects for EEG beta and in three subjects for peak velocity, with one subject showing a similar change for both parameters. Trait anxiety scores were higher on the first occasion (33 +/- 7) than on the second occasion (29 +/- 7; p < 0.01). A negative correlation was found between trait anxiety scores and the slopes of concentration-effect plots for peak velocity (r = -0.63; p < 0.01). CONCLUSIONS: For AUC and AUEC values the results indicate a reasonable long-term reproducibility of differences between subjects in the pharmacokinetics and pharmacodynamics of temazepam. However, there were limitations to the predictive value of derived concentration-effect parameters.

Adolescent↗
PubMed1994

Effect of anisotonic conditions on the transport of hydrophilic model compounds across monolayers of human colonic cell lines.

The effect of anisotonic solutions on the enhancement of the transport of hydrophilic model compounds across monolayers of Caco-2 and HT-29.cl19A intestinal epithelial cells was studied. In filter-grown monolayers of the highly differentiated villus-like Caco-2 cell line, a profound and dose-dependent drop in the transepithelial electrical resistance was found after apical treatment with a 30 or a 50% hypotonic solution (200 and 150 mOsmol, respectively). This drop was not observed after basolateral and two-sided application of a 50% hypotonic solution. During apical hypotonic treatment a 12- and 8-fold increase also was observed in transepithelial transport of two hydrophilic model compounds, i.e., fluorescein-Na and fluorescein-isothiocyanate-labeled dextran, MW 4000, respectively. Through confocal laser scanning microscopy, it was revealed that this enhanced transport was predominantly via the paracellular route. Moreover, morphological changes in the cell layers indicating cell swelling were observed after apical hypotonic, but not after basolateral or bilateral treatment, probably resulting from an incomplete regulatory volume decrease response. This swelling, and slight lateral retraction of the cells, allowed the hydrophilic compounds to pass between the cells. The effects of hypotonic challenge also were studied in monolayers of the more crypt cell-like HT-29.cl19A cell line. After apical hypotonic shock, these cells showed no effect on transepithelial electrical resistance, whereas an increase was observed after basolateral and bilateral treatment. Hypotonic shock failed to increase the transport of the hydrophilic model compounds in this cell line.(ABSTRACT TRUNCATED AT 250 WORDS)

Actins↗
PubMed1994

The influence of aging on the metabolism of simultaneously administered hexobarbital enantiomers and antipyrine before and after phenobarbital induction in male rats: a longitudinal study.

The influence of aging on the metabolism of antipyrine (AP) and hexobarbital enantiomers (R-HB and S-HB) with and without phenobarbital (PB) induction was investigated in a longitudinal study in rats aged 6, 12, 24 and 30 months. The metabolic clearances of AP (Clm AP), R-HB (Clm R-HB) and S-HB (Clm S-HB) were used as indicators for P450 enzyme activities in vivo. This also included the assessment of the clearances of formation of three AP metabolites, 3-hydroxymethylantipyrine (Cl-->HMA), 4-hydroxyantipyrine (Cl-->OHA) and norantipyrine (Cl-->NORA). Aging appeared to have little influence on the pharmacokinetics of the model compounds. By contrast, the influence of PB pretreatment on Clm AP changed dramatically with aging. The extent of induction decreased from 4.5-fold at 6 months to 1.7-fold at 30 months. Aging influenced the clearances of formation of the three metabolites differentially. Clm S-HB was about six times higher than Clm R-HB without induction. After PB induction, S-HB did not reach detectable levels in plasma at 6, 12 and 24 months. At 30 months, PB pretreatment resulted in a significantly decreased Clm S-HB when compared with the uninduced state. The extent of induction of R-HB metabolism had decreased strongly at 24 and 30 months. The present results clearly indicate that in the aged rat, the P450 enzyme system is much less sensitive to PB induction.

Aging↗