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PubMed2005

Retention versus sacrifice of the posterior cruciate ligament in total knee replacement for treatment of osteoarthritis and rheumatoid arthritis.

BACKGROUND: The functional and clinical results to support the choice whether or not to retain the posterior cruciate ligament (PCL) during total knee arthroplasty have not been gathered and analysed so far. There are at least some trials showing no difference. OBJECTIVES: To identify the difference in functional, clinical, and radiological outcome between retention and sacrifice of the PCL in total knee arthroplasty in patients with osteoarthrosis and other non-traumatic diseases. SEARCH STRATEGY: A search was conducted in MEDLINE(Through PubMed; 1966 - March 2004), EMBASE (1980 - March 2004), Cochrane Central Register of Controlled Trials (CENTRAL Issue 2004 - 1), and Current Contents (1996 - March 2004). Also, references of selected articles were checked and citation tracking on the articles selected was performed. SELECTION CRITERIA: Randomised controlled trials comparing retention to sacrifice of the PCL during total knee arthroplasty with regard to functional, radiological and clinical outcome in patients with osteoarthritis and other non-traumatic diseases were selected by two independent reviewers. DATA COLLECTION AND ANALYSIS: Methodological quality was assessed with the checklist by van Tulder and the Jadad list. Data was collected with a predeveloped form. Meta-analysis was performed with subgroup analyses on age, gender, disease severity, and follow-up time, if allowed by adequate power. MAIN RESULTS: Eight randomised controlled trials were found. Two treatment options were compared against PCL retention: PCL sacrifice without additional stabilisation (post and cam mechanism) (2 studies), and PCL sacrifice with posterior stabilized design (5 studies). One study included all three options. Range of motion was found to be 8.1 degrees higher in the posterior stabilized group compared to the PCL retention group (p=0.01, 95% confidence interval [1.7, 14.5]), although the heterogeneity was high (I(2 )= 66.3%). PCL resection without substituting the PCL with a posterior stabilised prosthesis showed no difference compared to PCL retention (p=0.31, I(2) = 83.2%). On clinical scores, only Hospital for Special Surgery score revealed a significant difference of 1.6 points (p=0.03, 95% confidence interval [-3.1, -0.1]) between PCL retention versus PCL sacrifice and substitution combined favouring the latter group. The necessary subgroup analyses could not be performed for the clinical scores. AUTHORS' CONCLUSIONS: These results should be interpreted with caution as the methodological quality of the studies was highly variable. We conclude that there is, so far, no solid base for the decision to either retain or sacrifice the PCL with or without use of a posterior stabilized design during total knee arthroplasty. The technique of PCL retention is difficult because the normal configuration and tension need to be reproduced with ligament tensioners. Knowledge of the technique needs to be improved before it can yield superior results compared to the more straightforward techniques of PCL sacrifice or use of a posterior stabilized design. Also, studies evaluating the effect of both techniques should address the right outcome parameters such as range of motion, contact position, and anterior-posterior stability. Suggestions are given to improve future research on this specific topic of knee arthroplasty.

Arthritis, Rheumatoid↗

PubMed1993

Retention of ascorbic acid in pickles--effect of different spices and salt (an in vitro study).

Effect of spices, different concentration of sodium chloride and other salts on retention of ascorbic acid during storage period (21 days in case of spices and eight days for salts) was studied. The retention of ascorbic acid with the addition of 24% NaCl was 55%, followed by 37% with red chillies, fenugreek, turmeric; 32% with the addition of pepper, sugar and 26% with mustard and asafoetida. When all the spices and salt were added together, the retention was much higher (73%) than those with individual spices. Sodium chloride over a wide range of concentrations was found to have higher retention of ascorbic acid. The retention being 80%, when stored with 24.0% sodium chloride solution for eight days. Sulfates of sodium, potassium, magnesium and manganese or chlorides of magnesium or manganese did not have a significant effect on the retention of ascorbic acid. The retention with potassium chloride was close to that observed with sodium chloride.

Ascorbic Acid↗

PubMed1990

The onset of sodium retention in experimental cirrhosis in rats is related to a critical threshold of liver function.

Although sodium retention is a common complication in advanced liver disease, the relationship between liver and kidney function in cirrhosis has not been well established. The objective of this study was to investigate this relationship in an experimental model of cirrhosis induced in phenobarbital-treated rats by weekly intragastric administration of carbon tetrachloride. Liver function, measured by the aminopyrine breath test, and urinary sodium excretion on a constant salt diet, were measured weekly. Administration of carbon tetrachloride led to cirrhosis, sodium retention, ascites and a reduction in liver function as measured by the amino pyrine breath test in all 15 rats surviving the first 8 wk. The time to develop sodium retention (defined as a decrease in urinary sodium excretion rate to less than 0.3 mmol/24 hr) varied from 9 to 19 wk. The aminopyrine breath test rate constant of elimination was reduced from 24 x 10(-3) min-1 +/- 2 x 10(-3) min-1 at the start of carbon tetrachloride administration by 61% +/- 10% at the time sodium retention occurred. A linear decrease was seen in aminopyrine breath test rate constant of elimination in the weeks preceding the onset of sodium retention. Sodium retention occurred when aminopyrine breath test rate contant of elimination was reduced to a critical threshold of 10 x 10(-3) +/- 1 x 10(-3) min-1, and then permitted to recover above this level by withdrawal of carbon tetrachloride. Sodium retention occurred when the aminopyrine breath test rate constant of elimination fell below the threshold; this was followed by spontaneous diuresis when aminopyrine breath test rate constant of elimination improved above 10 x 10(-3) +/- 1 x 10(-3) min-1.(ABSTRACT TRUNCATED AT 250 WORDS)

Aminopyrine↗

PubMed1992

Plant and mammalian sorting signals for protein retention in the endoplasmic reticulum contain a conserved epitope.

We studied protein sorting signals which are responsible for the retention of reticuloplasmins in the lumen of the plant endoplasmic reticulum (ER). A non-specific passenger protein, previously shown to be secreted by default, was used as a carrier for such signals. Tagging with C-terminal tetrapeptide sequences of mammalian (KDEL) and yeast (HDEL) reticuloplasmins led to effective accumulation of the protein chimeras in the lumen of the plant ER. Some single amino acid substitutions within the tetrapeptide tag (-SDEL, -KDDL, -KDEI and -KDEV) can cause a complete loss of its function as a retention signal, demonstrating the high specificity of the retention machinery. However, other modifications confer efficient (-RDEL) or partial (-KEEL) retention. It is also shown that the efficiency of protein retention is not significantly impaired by an increased ligand concentration in plants. The efficiently retained chimeras (-KDEL, -HDEL and -RDEL) were shown to be recognized by a monoclonal antibody directed against the C-terminus of the mammalian reticuloplasmin protein disulfide isomerase (PDI). The recognized epitope is also present in several putative reticuloplasmins in microsomal fractions of plant and mammalian cells, suggesting that the antibodies recognize an important structural determinant of the retention signal. In addition, data are discussed which support the view that upstream sequences beyond the C-terminal tetrapeptide can influence or may be part of the structure of reticuloplasmin retention signals.

Amino Acid Sequence↗

PubMed2004

The effect of different spray liquids on the foliar retention of agricultural sprays by wheat plants in a canopy.

The aim of this work was to examine the effect of liquid properties on spray retention in a range of situations representative of practical pesticide application. Liquids with different physical properties were sprayed with conventional flat-fan and air-induction nozzles onto outdoor-grown wheat plants (Triticum aestivum L cv Axona) at growth stages between GS 22 and GS 35. Since total retention is affected by leaf surface as well as plant growth stage and canopy density, the experiments included spraying both single leaves and groups of plants with different canopy densities. Retention on whole plants was strongly influenced by plant growth and canopy properties. Individual leaf surfaces were not as water-repellent as was found previously for younger indoor-grown plants, reducing the effect of dynamic surface tension on retention. This, combined with the increased probability of droplets hitting foliage in a denser canopy, gave reduced differences in retention between liquids when compared with similar measurements made previously on younger plants. With a leaf area index greater than 7, retention on whole plants was almost independent of liquid. Air-induction nozzles gave lower levels of retention than flat-fan nozzles, with this difference greatest when spraying high dynamic surface tension liquids and at low crop densities.

Agriculture↗

PubMed2003

Quantifying nitrate retention processes in a riparian buffer zone using the natural abundance of 15N in NO3-.

Quantifying the relative importance of denitrification and plant uptake to groundwater nitrate retention in riparian zones may lead to methods optimising the construction of riparian zones for water pollution control. The natural abundance of 15N in NO3- has been shown to be an interesting tool for providing insights into the NO3- retention processes occurring in riparian zones. In this study, 15N isotope fractionation (variation in delta15N of the residual NO3-) due to denitrification and due to plant uptake was measured in anaerobic soil slurries at different temperatures (5, 10 and 15 degrees C) and in hydroponic systems with different plant species (Lolium perenne L., Urtica dioica L. and Epilobium hirsutum L.). It was found that temperature had no significant effect on isotope fractionation during denitrification, which resulted in a 15N enrichment factor epsilonD of -22.5 +/- 0.6 per thousand. On the other hand, nitrate uptake by plants resulted in 15N isotope fractionation, but was independent of plant species, leading to a 15N enrichment factor epsilonP of -4.4 +/- 0.3 per thousand. By relating these two laboratory-defined enrichment factors to a field enrichment factor for groundwater nitrate retention during the growing season (epsilonR = -15.5 +/- 1.0 per thousand ), the contribution of denitrification and plant uptake to groundwater nitrate retention could be calculated. The relative importance of denitrification and plant uptake to groundwater nitrate retention in the riparian buffer zone was 49 and 51% during spring, 53 and 47% during summer, and 75 and 25% during autumn. During wintertime, high micropore dissolved organic carbon (DOC) concentrations and low redox potentials due to decomposition of the highly productive riparian vegetation probably resulted in a higher denitrification rate and favoured other nitrate retention processes such as nitrate immobilisation or dissimilatory nitrate reduction to ammonium (DNRA). This could have biased the 15N isotope fractionation and led to a low 15N enrichment factor for groundwater nitrate retention during wintertime (-6.2 +/- 0.9 per thousand ). In contradiction to what many other studies suggest, it is possible that due to plant decomposition during the winter period other nitrate transformation processes compete with denitrification.

Journal Article↗

PubMed1993

The signal for retention of the egasyn-glucuronidase complex within the endoplasmic reticulum.

Egasyn is localized within the lumen of the endoplasmic reticulum (ER) where it complexes with and thus causes sequestration of a considerable portion of beta-glucuronidase. Egasyn has an HTEL sequence at its carboxyl terminus rather than the KDEL sequence that serves as a retention signal for many ER lumenal proteins. To determine whether the HTEL sequence acts as an ER retention signal and/or functions in complex formation, HTEL-deleted egasyn was expressed in mammalian cell lines. The majority of HTEL-deleted egasyn was secreted, while wild type egasyn was retained in the ER. Furthermore, the egasyn HTEL sequence, when added to the carboxyl termini of two secretory proteins, mouse esterase, Es-N, and rat alpha 1-acid glycoprotein (AGP), caused retention of both proteins within the ER, demonstrating that the HTEL sequence is both necessary and sufficient for retention of egasyn and, by extension, the egasyn-glucuronidase complex within the ER. Other carboxyl terminal tetrapeptides including HIEL and HVEL, naturally occurring in other ER lumenal proteins, were also sufficient for ER retention of AGP, while HTEHT and HTEHK were inefficient in ER retention. The HTEL sequence, in contrast, is not required for egasyn-glucuronidase complex formation. Further, the complex is apparently unstable outside the ER since it was not visible in the medium of cells transfected with egasyn lacking the HTEL sequence despite abundant secretion of this egasyn. These results show that it is possible to localize proteins within the lumen of the ER if they form complexes with ER lumenal proteins containing an intrinsic ER retention sequence.

Amino Acid Sequence↗

PubMed2000

Involvement of central cholinergic mechanisms in the effects of oxytocin and an oxytocin receptor antagonist on retention performance in mice.

Oxytocin (OT, 0.10 microg/kg, sc) impaired retention of a one-trial step-through inhibitory avoidance task when injected into male Swiss mice 10 min after training, as indicated by retention performance 48 h later. In contrast, the immediate post-training administration of the putative oxytocin receptor antagonist d(CH(2))(5)[Tyr(Me)(2), Thr(4), Thy-NH(9)(2)] OVT (AOT, 0.30 microg/kg, sc) significantly enhanced retention performance. Neither OT nor AOT affected response latencies in mice not given footshock on the training trial, and neither the impairing effects of OT nor the enhancing effects of AOT were seen when the training-treatment interval was 180 min, suggesting that both treatments influenced memory storage. The effects of OT (0.10 microg/kg, sc) on retention were prevented by AOT (0.03 microg/kg, sc) given immediately after training, but 10 min prior to OT treatment. The central acting anticholinesterase physostigmine (35, 70, or 150 microg/kg, i.p.), but not its quaternary analogue neostigmine (150 microg/kg, i.p.), reversed the impairment of retention performance induced by OT, whereas low subeffective doses of the centrally active muscarinic cholinergic antagonist atropine (0.5 mg/kg, i.p.) or the central acting nicotinic cholinergic antagonist mecamylamine (5 mg/kg, i.p.), but not methylatropine (0.5 mg/kg, i.p.) or hexamethonium (5 mg/kg, i.p.) prevented the enhancement of retention performance caused by AOT. We suggest that oxytocin negatively modulates the activity of central cholinergic mechanisms during the posttraining period that follows an aversively motivated learning experience, leading to an impairment of retention performance of the inhibitory avoidance response.

Acetylcholine↗

PubMed1988

Post-training administration of GABAergic antagonists enhances retention of aversively motivated tasks.

The effect of sub-convulsive doses of GABAergic antagonists on the retention of two aversively motivated tasks, inhibitory avoidance (IA) and Y-maze discrimination (YMD), was investigated in CFW mice. In the IA task, post-training intraperitoneal injections of picrotoxin and bicuculline induced a dose-dependent enhancement of retention measured 24 h after the training, while retention was not affected by bicuculline methiodide (a GABA receptor antagonist that does not readily cross the blood-brain barrier). In the absence of footshock on the training day, post-training administration of picrotoxin and bicuculline did not affect retention test latencies. In the YMD task, the discrimination was reversed on the retention test and errors made on the reversal trials served as the index of retention of the original training. The reversal error scores of mice given post-training injections of picrotoxin or bicuculline, but not bicuculline methiodide, were significantly higher than those of saline-treated controls. These findings extend previous observations that GABAergic antagonists enhance retention of aversively motivated tasks and suggest the involvement of central GABAergic processes on memory consolidation.

Animals↗

PubMed2002

Retention and stability--taking various treatment parameters into account.

PATIENTS AND METHOD: In order to assess stability after orthodontic treatment, 132 patients who had been treated by one orthodontist in private practice were examined 6 years on average after completion of their treatment. Therapeutically induced movements and post-therapeutic changes were measured using dental casts, and the number of cases which had relapsed was calculated as a percentage of the individual measurements. The extent of post-therapeutic changes in patients with and without long-term retention was analyzed together with possible correlations with retention time and retainer type. Furthermore, the influence of gender, Angle classification, treatment-induced changes, initiation, type and duration of therapy, and extraction of premolars on the development of relapse was also investigated. RESULTS AND CONCLUSIONS: Some degree of relapse was recorded in 13% of the measurements on average, even in patients with some form of long-term retention. However, it may be possible to reduce the relapse rate by taking account of the following criteria: Retention time should be increased in cases of short-term therapy, since relapse was found to occur more often on average (19%) when the treatment time was less than 3 years than when it was longer than 4 years (13%). As the highest relapse rate registered was 24% when therapy was started between the ages of 9 and 12 years, but was up to 42% in younger and older patients, there should be more extensive retention in these latter cases. Where there is a risk of relapse in the anterior arch, fixed lingual retainers should be given preference over removable ones. This is especially applicable to male patients and to non-extraction patients, as relapses in the anterior segment occurred more often or were more marked in these cases. The use of removable retainers is necessary when the transverse stability of the buccal segment is at risk. When only fixed retainers were used in the anterior area, relapses were recorded 6-31% more frequently in the interpremolar distance in the maxilla (21%) and the mandible (35%), and in the lower intermolar distance (27%). In particular, the use of a removable mandibular retainer should not be dispensed with after bicuspid extractions, transverse expansion and, in female patients, in the lower jaw, as relapse in the buccal segment was more marked or more common in such cases. On the basis of our clinical findings and of earlier studies, the retention time should be at least 2 years. The retainer type used has been found to be just as important as the retention time. If optimum relapse prevention is aimed at, fixed maxillary and mandibular retainers in the anterior region should be combined with a removable retainer and worn until the patients reach their late twenties.

Adolescent↗

PubMed2003

Transmural migration of gastrostomy tube retention discs.

BACKGROUND: Accidental dislodgment is one of the most frequent causes of avoidable cost and consternation related to gastrostomy tubes. The Sacks-Vine gastrostomy tube, inserted in an antegrade fashion by a percutaneous technique, is extremely stable due to the construction of its disc retention device. However, transmural migration of the retention disc is a known severe delayed complication associated with this tube. OBJECTIVE: To review the presentation, diagnosis, and treatment of transmural migration of gastrostomy retention discs, to propose a mechanism for the progressive development of this complication, and to recommend a method for preventing its occurrence. MATERIALS AND METHODS: From January 1991 to October 1999, pediatric interventional radiologists at two children's hospitals performed 300 antegrade gastrostomy and gastrojejunostomy primary insertion procedures. A "push-pull" variation of the antegrade approach used for 44 of these insertions is excluded from further analysis. Of the remaining 256 procedures, 5 boys and 3 girls with a mean age of 5.1 years (range 0.8-19 years) were identified from review of the prospectively gathered procedural database with significant complications related to the disc retention component of their gastrostomy tubes. A retrospective analysis was conducted of their medical records, diagnostic imaging, and interventional and surgical findings. RESULTS: Transmural migration was diagnosed on average 36 months after insertion (16-48 months). The diagnosis was made incidentally during endoscopy (n=1) or fluoroscopy (n=5) in six asymptomatic patients, and during barium enema to explore feculent vomiting and halitosis in two symptomatic patients. Migration of the retention disc fell along a continuum from intramural (n=4) to transmural and intracolonic (n=4), with gastric mucosal erosion, extensive granulation and inflammation in all eight patients. Although there was no evidence of free air in any patient, a gastrocolic fistula was demonstrated in four patients and a gastrocolocutaneous fistula in two of four patients with complete transmural migration. Surgical resection of the disc, gastrostomy, and fistula repair if needed was successfully performed in all patients. CONCLUSIONS: Gastrostomy tubes with an internal retention disc are at risk for progressive disc migration into and through the gastric wall, resulting in irretrievable fixation and potential fistula formation. This severe delayed complication results from prolonged traction on the retention disc. Transmural migration may be avoided through improved tube care education, daily disc mobilization, and earlier disc retrieval.

Adolescent↗

PubMed2005

Low temperature promotes intron retention in two e-cor genes of durum wheat.

Following the screening of a suppression subtractive library developed from durum wheat plants exposed to low temperature for 6 h, two early cold-regulated (e-cor) genes have been isolated. These genes, coding putatively for a ribokinase (7H8) and a C3H2C3 RING-finger protein (6G2), were characterized by the stress-induced retention of a subset of introns in the mature mRNA. This feature was dependent on cold for 7H8 and on cold and dehydration for 6G2. When other genes, such as the stress-related gene WCOR410c, coding for a dehydrin (one intron), or a gene coding for a putative ATP binding cassette transporter (16 introns) were analyzed, no cold-dependent intron retention was observed. Cold-induced intron retention was not observed in mutants defective in the chloroplast development; nevertheless treatment with cycloheximide in the absence of cold was able to promote intron retention for the 7H8 e-cor gene. These results suggest that the cold-induced intron retention reflects the response of the spliceosoma to specific environmental signals transduced to the splicing protein factors through a chloroplast-dependent pathway. Notably, when the 7H8 Arabidopsis orthologous gene was analyzed, no stress induction in terms of mRNA abundance and no cold-dependent intron retention was detected. Otherwise, 6G2 Arabidopsis homologous sequences sharing the same genomic structure of the durum wheat 6G2 showed a similar intron retention event although not strictly dependent on stress.

Arabidopsis↗

PubMed2008

Mate retention behavior of men and women in heterosexual and homosexual relationships.

Comparing the behavior of heterosexual and homosexual persons can provide insight into the origins of heterosexual sex differences in psychology. Evidence indicates that, aside from sexual partner preference, the mating psychology of homosexual men is sex-typical whereas that of homosexual women tends to be more sex-atypical. The current study examined one aspect of mating psychology, mate retention behavior, and tested whether homosexual men and women were sex-typical or sex-atypical for those mate retention tactics where heterosexual men and women differed. Men and women in heterosexual and homosexual relationships were asked to provide information regarding their partners' mate retention behavior by using the Mate Retention Inventory Questionnaire. Heterosexual men and women differed significantly for six of the 19 mate retention tactics considered. With respect to the six mate retention tactics where heterosexual sex differences existed, homosexual men behaved in a sex-typical manner for five of the tactics, whereas homosexual women behaved in a sex-atypical manner for all six tactics. We discuss the significance of these findings for explaining the origins of the mate retention behavior of heterosexual men and women. In addition, we consider what the pattern of sex-typical and sex-atypical mating psychology among homosexual men and women, respectively, suggests in regard to sex differences in the development of mating psychology and the development of homosexual persons.

Adolescent↗

PubMed1981

Effect of surface contamination on band retention.

Laboratory investigations on the retention of orthodontic bands have been concerned with testing the retentive strength of different cements. This study reported here was designed to evaluate the effect of tooth-surface contamination on band retention. Zinc phosphate, silicophosphate, and polycarboxylate (powder: liquid ratio 1.5:1 and 1:1) cements were each tested on different groups of ten teeth. Preformed bands were selected, prepared, and cemented under controlled conditions. Specially designed jigs were used for cementing and for testing. For each cement, the tooth surfaces were pretreated prior to cementing as follows: (1) cleaned with pumice, (2) covered with wet saliva, (3) covered with saliva which was allowed to dry, and (4) covered with liquid paraffin. All specimens were stored in water at 37 degrees C. for 1 week prior to testing. Retention values were established by determining the tensile load required to dislodge the band divided by the surface area of the band. The retention of bands cemented with zinc phosphate and silicophosphate cements was unaffected by contamination of the enamel. The presence of dry saliva and of liquid paraffin significantly reduced the retention of bands cemented with polycarboxylate (P:L 1,5:1) (P less than 0.01). Only the presence of dry saliva reduced band retention when polycarboxylate (P:L 1:1) was used (P less than 0.05).

Acrylic Resins↗

PubMed1991

Delayed exposure to pulsatile shear stress improves retention of human saphenous vein endothelial cells on seeded ePTFE grafts.

Since significant loss of endothelial cells (ECs) from the surface of a seeded prosthetic graft occurs after implantation, improved cell retention following exposure to flow should increase the likelihood of long-term success with this technology. An in vitro pulsatile flow circuit was developed to study the effects of two variables on cell retention: cell density at the time of seeding and postseeding incubation time. Fibronectin-coated ePTFE grafts (4 mm x 5 cm) were seeded with human saphenous vein ECs at two densities, confluent (1 x 10(5) cells/cm2) or subconfluent (2 x 10(4)), and incubated in vitro for varying time intervals (90 min, 1, 3, or 7 days). Test grafts were exposed to 90 min of pulsatile flow in an in vitro flow circuit, then fixed, and stained, and in situ cell counts (cells/cm2) were determined for nine representative fields per graft. Paired control grafts were treated identically but were not exposed to flow. Cell retention was calculated using the formula: % retention = cells/cm2 perfused graft divided by cells/cm2 control graft. Grafts exposed to flow 90 min after seeding demonstrated significantly lower cell retention when compared to later time points. When cells were seeded at confluent density, maximal retention (92 +/- 3%) occurred 24 hr after seeding. Prolonged culture of cells seeded on ePTFE grafts at confluent density resulted in increased cell loss. In contrast, on grafts seeded at subconfluent density, retention improved as cells grew to confluence (16 +/- 4.5% initially to 82 +/- 7% at 7 days).(ABSTRACT TRUNCATED AT 250 WORDS)

Blood Vessel Prosthesis↗

PubMed1983

Cation exchange contribution to the retention of specific quaternary ammonium compounds in reversed-phase high-performance liquid chromatography.

The influence of electrolytes on the retention of organic cationic solutes in reversed-phase high-performance liquid chromatography (RP-HPLC) has been investigated. The effects of the nature and concentration of electrolytes and mobile phase pH on the retention of two model quaternary ammonium compounds were studied on mu-Bondapak C18 stationary phase with aqueous methanolic eluents. The nature and concentration of inorganic cations added to the mobile phase modified the retention of the solutes. The counter anion of the added electrolyte did not perceptibly influence solute retention at constant mobile phase pH, although it did significantly influence solute retention when the electrolytes were added to unbuffered mobile phases. The retention data are consistent with the inclusion of an ion exchange contribution to the retention of cationic solutes in the systems investigated.

Journal Article↗

PubMed1996

Half-fraction and full factorial designs versus central composite design for retention modelling in reversed-phase ion-pair liquid chromatography.

In a previous paper (J. O. De Beer, C. V. Vandenbroucke and D. L. Massart, J. Pharm. Biomed. Anal., 12, (1994) 1379-1396) liquid chromatographic (LC) retention modelling of the cough-syrup compounds methyl para-hydroxybenzoate (MPHB) and propyl para-hydroxybenzoate (PPHB), phenylephrine hydrochloride (PE) and chlorphenamine maleate (CPM) was studied using a face-centred central composite design. It is examined whether smaller half-fractional and full factorial designs with fewer experiments tend to reliably predict retention times of the latter compounds as well. Simplified regression modelling, however, neglecting more first-order and interactive effects and disregarding pure second-order effects, has to be set up. These smaller designs finally satisfy the prediction of the retention of MPHB, PPHB and PE also. Retention prediction of CPM is much less accurate. CPM has a pKa value of 4.0, which is encompassed by the examined mobile phase pH limits 3.0 and 5.0. Since the largest retention shifts occur near the pKa value, retention prediction in this area becomes more complex. CPM retention modelling from a full factorial design is useful if the mobile phase pH is fixed at 5.0 for methanol as well as for acetonitrile as organic modifers. The full factorial design, applied with acetonitrile as organic modifer, enables the selection of suitable LC parameter combinations for fast and complete separation of the four compounds in cough-syrup analysis.

Chemical Phenomena↗

PubMed1992

Comparison of technetium-99m sestamibi and thallium-201 retention characteristics in canine myocardium.

OBJECTIVES: The aim of this study was to compare the myocardial retention of technetium-99m (Tc-99m) sestamibi and thallium-201 over a wide range of blood flow at different time points after tracer injection. BACKGROUND: Technetium-99m sestamibi has been proposed as a new perfusion tracer with better physical characteristics than those of thallium-201 for scintigraphic imaging. However, no studies have simultaneously compared the ability of both tracers to assess myocardial blood flow during pharmacologic vasodilation. METHODS: The myocardial retention of Tc-99m sestamibi and thallium-201 were compared over a wide range of blood flow induced by regional coronary occlusion and dipyridamole infusion in an open chest dog model. Myocardial retention of both tracers was determined by in vitro tissue counting at 2, 5, and 20 min after tracer injection and was correlated with microsphere-determined blood flow. RESULTS: Thallium-201 demonstrated greater absolute tissue retention than did Tc-99m sestamibi. At 2 min after tracer injection, there was an almost linear relation between the retention of both tracers and myocardial blood flow over a wide flow range. However, this relation was not maintained over time. At 20 min after injection, the retention of both tracers underestimated myocardial blood flow at higher flow rates. At 2, 5 and 20 min after injection, increments of relative tracer retention between the different levels of flow were always greater for thallium-201 than for Tc-99m sestamibi. CONCLUSIONS: Thallium-201 displays more suitable physiologic characteristics as a flow tracer and may allow better differentiation of myocardial regions with different levels of coronary flow reserve. For both tracers, early cardiac imaging may minimize underestimation of blood flow at higher flow rates.

Animals↗