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PubMed2001

[A new method for predicting retention time of solutes under linear gradient elution conditions in RP-HPLC].

A new method for predicting the retention time of solutes under linear gradient elution has been established. In this method, the migration distance of solutes in column and the mobile phase gradient were modified simultaneously according to the distribution of mobile phase in column. The prediction results of retention time of both weakly and strongly retentive solutes were accurate in different instrumental systems using this method. In order to test and verify this method, the retention time of fifteen amino acids and eight homologous compounds of benzene were predicted. The predicted results were compared with those predicted by the method in common use. The relative average errors between predicted and experimental values were 3.70% and 4.90% for the weakly retentive solutes, far smaller than those obtained by the reference method (23.61% and 31.16%). For the strongly retentive solutes, the relative average errors were 0.21% and 6.01% respectively, slightly smaller than those obtained by the reference method (0.81% and 6.69%). It is seen that this new method has many advantages.

Amino Acids↗
PubMed2004

Influence of inorganic mobile phase additives on the retention, efficiency and peak symmetry of protonated basic compounds in reversed-phase liquid chromatography.

Inorganic eluent additives affect the retention of protonated basic analytes in reversed-phase HPLC. This influence is attributed to the disruption of the analyte solvation-desolvation equilibria in the mobile phase, also known as "chaotropic effect". With an increase of counteranion concentration analyte retention increases with concomitant decrease in the tailing factor. Different inorganic counteranions at equimolar concentrations affect protonated basic analyte retention and peak symmetry to varying degrees. The effect of the concentrations of four different inorganic mobile phase additives (KPF6, NaClO4, NaBF4, NaH2PO4) on the analyte retention, peak symmetry, and efficiency on a C8-bonded silica column has been studied. The analytes used in this study included phenols, toluene, benzyl amines, beta-blockers and ophthalmic drugs. The following trend in increase of basic analyte retention factor and decrease of tailing factor was found: PF6- > ClO4- approximately BF4- > H2PO4-. With the increase of the counteranion concentration greater analyte loading could be achieved and consequently an increase in the apparent efficiency was observed until the maximum plate number for the column was achieved. At the highest concentration of counteranions, the peak efficiency for most of the basic compounds studied was similar to that of the neutral markers. In contrast, the neutral markers, such as phenols, showed no significant changes in retention, efficiency or loading capacity as counteranion concentration was increased.

Algorithms↗
PubMed2004

Rural GPs' ratings of initiatives designed to improve rural medical workforce recruitment and retention.

INTRODUCTION: Since the early 1990s, Australian governments have recognised the problems of rural medical workforce recruitment and retention and have implemented a range of programs and incentives designed to improve the supply of, and access to, doctors in rural and remote areas. Some incentives involve differential payments according to degree of rurality or remoteness. Since these programs involve considerable costs to governments, some assessment of their impact on recruitment or retention is warranted. The objective of this study is to examine the effectiveness of different recruitment and retention incentives from the perspective of the rural GP. Doctors practising in rural and remote communities were, therefore, asked to rank the relative importance of different interventions in terms of their impact on recruitment to and retention of GPs in their communities. METHODS: Six possible interventions were selected to cover the major objectives underpinning rural workforce programs most relevant to doctors currently in rural practice. Respondents assigned a rank to indicate the relative importance of each item with respect to each of the two questions: "What would help most to attract more GPs to this community?" and "What would help most to retain GPs in this community?" The data were collected as part of a national study into the viability of rural general practice undertaken jointly by the Rural Doctors Association of Australia and Monash University School of Rural Health Bendigo. The Rural, Remote and Metropolitan Areas (RRMA) classification was used as the rurality indicator. Analysis involved the calculation of mean ranks for each item. Item means were then ranked to indicate most to least important items in total, and within each RRMA category. RESULTS: Thirty-five percent of all GPs practising in rural and remote Australia responded to the national survey, representing 53% of all practices in those areas. Of these, 1050 doctors who nominated themselves as a principal, partner or associate in their practice were eligible for inclusion in this analysis. The results showed a high degree of agreement in the responses to both questions, with the possible interventions being ranked in the same overall order. 'Better remuneration for Medicare consultations' and 'Improved after-hours and on-call arrangements' were ranked as the most important interventions for both attracting and retaining GPs, whereas 'Better education and professional support activity' and 'Improved availability of allied health professional services' were ranked as least important of the options presented. 'Better locum availability' and 'Capital funding to improve practice infrastructure/enable GPs to set up practice' ranked in between. Results within each RRMA category were very similar to the overall rankings, confirming the significance of the improved remuneration and workload arrangements, regardless of geographical location. CONCLUSIONS: Ensuring professional support, workforce supply, income and infrastructure support are all relevant to the recruitment and retention of GPs in rural and remote areas. However, from the perspective of GPs practising in such areas, specific initiatives that increase the core income of rural practices, and which address those medical workforce supply issues which impact most on workload, are considered those which are most likely to assist in the recruitment and retention of GPs to Australia's rural and remote communities.

Journal Article↗
PubMed1991

Sodium retention and hepatic function after two-thirds hepatectomy in the rat.

Recently it was suggested that the onset of sodium retention in experimental cirrhosis in rats is related to a critical threshold of hepatic function, as assessed by the aminopyrine breath test. The aim of this study was to evaluate whether sodium retention occurred after two-thirds hepatectomy in rats and to investigate the relationship between sodium retention and changes in hepatic function associated with liver regeneration in this model. Sodium balance, creatinine clearance, serum sodium and the aminopyrine rate constant of elimination were evaluated daily for 4 days after surgery in partially hepatectomized (n = 6) and sham-operated rats (n = 6). All rats in the partial hepatectomy group exhibited sodium retention (sodium balance greater than 0.7 mmol/day) 24 hr after surgery. This was associated with a 62% reduction of the aminopyrine rate constant of elimination. Spontaneous natriuresis which occurred between 2 and 4 days after surgery, was associated with an increase in the aminopyrine rate constant of elimination (from 0.73 +/- 0.02 x 10(-2) min-1 on the last day of sodium retention to 0.95 +/- 0.04 x 10(-2) min-1 on the first day of natriuresis [p less than 0.05]). In contrast, no change in creatinine clearance occurred over the same period. A negative curvilinear association was found between sodium balance and the aminopyrine rate constant of elimination in all animals (r = -0.72, p less than 0.001). These observations indicate that natriuresis is related to the recovery of liver function, not to changes in creatinine clearance. In conclusion, the concept of a critical threshold of liver function below which sodium retention occurs has been substantiated in this model of hepatic dysfunction.

Analysis of Variance↗
PubMedDate not supplied

Pathophysiology of experimental nephrotic syndrome induced by puromycin aminonucleoside in rats. I. The role of proteinuria, hypoproteinemia, and renin-angiotensin-aldosterone system on sodium retention.

The pathophysiology of the nephrotic syndrome (NS), characterized by protenuria, edema, sodium retention and hyperlipidemia, is not clear. We studied the role of some systemic factors on sodium retention in an experimental model of NS. NS was induced in rats by a single subcutaneous injection of puromycin aminonucleoside (PA) (15 mg/100 g); control animals received vehicle. All rats were kept in metabolic cages for 24 days (3 days before and 21 days after PA-injection). Urine was collected daily. Blood samples were obtained every day until day 10, and then every other day up to the end of the study. The rats showed the following alterations after PA injection: a) a rise in serum angiotensin converting enzyme activity (ACEA) and plasma aldosterone (PAldo) at day 1; b) a rise in urinary aldosterone (UAaldoV), azotemia and sodium retention at day 2; c) massive proteinuria (UProt) and decrease in plasma angiotensinogen concentration (PAC) at day 4; d) increases in plasma renin activity (PRA), plasma renin concentration (PRC) and serum creatinine as well as hypoproteinemia, hypercholesterolemia, hypertriglyceridemia, ascitis and edema at day 5; e) increase in urine volume at day 6. PAldo became normal at day 7; urine sodium (UNaV), PRA and PRC at day 8; UAldoV at day 9; serum urea and ACEA at day 10; urinary volume at day 11; PAC, serum total protein and creatinine at day 12. The edema disappeared at day 11. UProt, hypercholesterolemia and hypertriglyceridemia persisted, though they decreased substantially by the end of the study (day 21). Light microscopy studies revealed normal glomerular morphology, but electron microscopy showed fusion of podocytes before proteinuria. These data suggest that: a) sodium retention was not a consequence of proteinuria or hypoproteinemia; b) sodium retention seems non-related to renin secretion, but may be partially mediated by a fall in glomerular filtration rate or by an increased tubular resabsorption secondary to other factors; c) the increase in PAldo, UAldoV and ACEA are non-related to renin secretion: all occurred before PRA rose; d) water retention, increase in PRA and PRC, hypercholesterolemia and hypertriglyceridemia are secondary to the hypoproteinemia.

Animals↗
PubMed1989

Learning and retention of active avoidance are differently impaired after dorsal and ventral lesions of the nucleus reticularis pontis caudalis of rats.

Four groups of 8 adult male hooded rats of the Long-Evans strain were investigated before and after bilateral symmetric lesions of the nucleus reticularis pontis caudalis (RPC) in a Y-maze and in a jump test box. After dorsal (d) RPC lesions the retention of preoperatively learnt simple tasks in the Y-maze or in the jump test was not impaired whereas brightness discrimination in the Y-maze was neither retained nor relearned. Postoperative acquisition without preoperative experience was impossible for dRPC rats in any of the tests. After ventral (v) RPC lesions there was no retention of active avoidance response in the Y-maze but rather normal retention of the jump test performance. The retention of brightness discrimination, however, was not impaired in the Y-maze after vRPC lesions. The relearning of the impaired active avoidance in the Y-maze was impossible for vRPC rats; though these rats showed intrasessional improvement, there was no retention between sessions. After retention of the simple jump test task the vRPC rats were not able to learn a go/no-go task in the jump test box. Acute extinction to the non-reinforced 2.5 KHz tone was prolonged. Intertrial responses in the jump test were reduced to zero after dRPC lesions, but significantly enhanced after vRPC lesions. The results indicate that CAR response initiation was reduced after dRPC lesions, but in vRPC rats the suppression of incorrect responses was reduced in the jump test. The lesions differently impair the control of learnt motor programs.

Animals↗
PubMed1989

The effects of surface configuration on the retentive properties of parallel-sided dowels cemented with a composite luting agent.

Factors which have effect on the retention of any dowel include the shape, length, diameter, and surface configuration of the dowel, the cementing medium, precision fitness and material, etc. The shape and surface configuration are the most important among all factors. Recent developments of the etching technique for cast metal has improved the bonding strength between base metal alloys and composite cement which offers a great opportunity for better retention of the dowel if its surface has been etched. In the past, because it has often been ignored that the bonding at the cement-dentin interface is weaker than that between the metal and cement, the true impact of surface configuration and cement thickness on the retention of dowels has never really been observed. In this study, plastic transparent rods were substituted for natural teeth to avoid anatomical variation and circular horizontal grooves were placed on the channel walls to strengthen the retention between the cement and the plastic rods. A total of 140 dowel samples were cast in Rexillium III and were divided into seven groups. The surfaces of the samples were treated differently by smoothing, sandblasting, chemical etching, electrolytic etching and serrating, and fixed into the channels of the plastic rods by cementation with composite resin. Immediately thereafter, the samples were submerged in 37 degrees C water for 7 days. Instron crosshead speed 1 mm/min was used in measuring the tensile forces required for extracting the dowels from the channels. Data were analyzed with the ANOVA method. Among the three factors known to have an effect on the retention being considered in this study, the circular horizontal groove proved to be the most influential, and surface configuration came next, while cement thickness was the least influential. Among the different surface configurations, the serrated dowels showed the best retention and were followed in order by etched and smooth or sandblasted dowels.

Biocompatible Materials↗
PubMed1986

The relationship between protein retention and energy requirements in rats of different ages.

Male Wistar rats aged 30, 75 and 150 days were fed for 14 days ad libitum on diets with an optimum protein content (15% for 30-day-old, 12.5% for 75-day-old and 10% for 150-day-old animals) and a mounting fat content (from 5 to 40%), supplemented by saccharides (from 76 to 41%). Net protein utilization was determined for each of the diets from the body nitrogen and protein intake values. Protein retention values were determined from protein intake on the basis of net protein utilization (NPU). Energy intake was computed from fat and saccharide intake, using energy coefficients. The optimum fat content of the diet, evaluated from the maximum protein retention value per day and the minimum amount of energy needed for the retention of 1 g protein, is 30% at 30 days, 15% at 75 days and 10% at 150 days. Protein retention per kg body weight falls with advancing age--mildly at 75 days compared with 30 days, but markedly at 150 days. From their smaller weight increments and NPU values and also from their lower protein retention, 150-day-old animals are characterized by slower growth and higher protein requirements for maintenance of their organism likewise demonstrated by the growth parameter net protein ratio (NPR). Energy requirements for total protein retention/day per kg body weight diminish with age. In old age a small amount of energy is needed only for the maintenance of body functions. This study contributes to the expression of the interrelationship of energy requirements and protein retention.

Age Factors↗
PubMed1987

[A modified in vivo platelet retention test in the evaluation of primary hemostasis].

A simple assay system for measuring platelet retention in a standardized superficial skin wound is presented. Platelets were counted in the blood collected at the site of the wound 1, 2 and 3 minutes following incision. Per cent platelet retention was calculated from the difference between venous blood platelet count and wound blood platelet count, divided by venous count. The time course of platelet retention, measured in 20 healthy persons, reflected the sequence of primary and secondary platelet aggregation. Ten patients with congenital platelet defects already showed impaired platelet retention in the early stage of bleeding. On the other hand, administration of aspirin to 10 healthy subjects inhibited only the late stage of platelet retention. In comparison with the template bleeding time our platelet retention test provides additional information useful for evaluating congenital and drug-induced defects in platelet plug formation.

Aspirin↗
PubMed1987

Effect of gavaged chemical form of 241Am on its retention in mice.

The retention of 241Am in mice 48 h after administration by gavage is reported here. The 241Am was given to mice in the form of either 241Am nitrate or 241Am citrate. The 241Am was also injected into rats in the same form. The homogenized livers of those rats were subsequently administered by gavage to another group of mice. The retention of 241Am citrate was 1.5 X 10(-2)% of the original dose and was the highest among the compounds examined. The retention of biologically incorporated 241Am into the liver as 241Am nitrate and as 241Am citrate was 2.4 X 10(-3) and 2.6 X 10(-3)%, respectively, and was similar to the retention of 241Am nitrate, which was 2.8 X 10(-3)%. The ratio of the retention in the carcass to that in the liver for the 241Am citrate was lower than that of the 241Am nitrate and the biologically incorporated 241Am. This difference indicates that the distribution of 241Am in the animal body depends on the chemical form administered. The retention of liver-incorporated 241Am as citrate after autolysis of the liver is similar to that of fresh liver-incorporated 241Am citrate.

Americium↗
PubMed1985

Mitochondrial and plasma membrane potentials cause unusual accumulation and retention of rhodamine 123 by human breast adenocarcinoma-derived MCF-7 cells.

Quantitative studies of MCF-7 cells (derived from human breast adenocarcinoma) and CV-1 cells (from normal African green monkey kidney epithelium), using the permeant cationic compound tetraphenylphosphonium (TPP), in conjunction with fluorescence microscopy using rhodamine 123 (Rh123), indicate that the mitochondrial and plasma membrane potentials affect both uptake and retention of these compounds. Under conditions that depolarize the plasma membrane, uptake and retention of TPP and Rh123, driven only by the mitochondrial membrane potential, is greater in MCF-7 than in CV-1. An ionophore that dissipates the mitochondrial membrane potential of MCF-7 cells causes them to resemble CV-1 cells by decreasing uptake and retention. Hyperpolarizing the mitochondrial membrane of CV-1 increases accumulation and prolongs retention; hyperpolarization of the plasma membrane further heightens this effect, causing the uptake of CV-1 cells to resemble that of MCF-7 cells even more closely. The greater uptake and retention by MCF-7 appears to be a consequence of elevated mitochondrial and plasma membrane potentials. The plasma membrane potential affects mitochondrial retention of TPP and Rh123 and its role in enhancing the effect of a difference in mitochondrial membrane potential is explained.

Adenocarcinoma↗
PubMed1984

Retention and dosimetry of injected 241Am in beagles.

Equations have been derived, from the results of total-body and partial-body counting and gamma-ray counting of individual bones and soft tissues, which describe the retention of injected 241Am in the liver, in the nonliver tissue (including skeleton), and in the skeleton of young adult beagles. Retention was found to be dependent upon injection level, and different sets of equations were developed for dogs given about (a) 2.8 microCi/kg (b) 0.9 microCi/kg (c) 0.3 microCi/kg, and (d) 0.1 microCi/kg and less. Liver rention, RL, was characterized by a single exponential equation of the form RL = ce-beta t, with c = 0.49 +/- 0.04 and beta = a function of injection level. Nonliver tissue was assigned a retention equation of the form RNL = d + alpha + J(l - e-mt), with d = 0.102 +/- 0.024 e-1.22t, alpha = 0.41 +/- 0.04, and both J and m as a function of injection level. Skeletal retention was found to be about 0.885 +/- 0.037 of nonliver retention with no significant dependence upon either injection level or time after 241Am injection. Dosimetry equations based on these retention expressions were derived. Individual bones of 55 beagles were assayed at death for their 241Am content for a determination of 241Am distribution within the skeleton.

Americium↗
PubMed1981

[Effect of the position of the container in the retention of nutrients in food models heated by natural convection].

The existence of statistically significant differences in the nutrient retention of products heated by natural convection in cylindrical containers of equal size when thermally processed in vertical and horizontal position was studied. The thiamine retention was found to be significantly greater for containers placed in vertical position. A modification to the model proposed by Barreiro (4) for the prediction of nutrient retention during thermal processing of vertically placed canned model systems heated by natural convection was also developed to adapt it to containers processed in a horizontal position. To achieve this goal, an equivalent characteristic length was found for the vertically placed containers, and several changes were introduced. The modified model was then evaluated through ten experiments with different thermal processing parameters. The theoretical thiamine retention values predicted by the model wee compared with the experimental retention. In all cases they were within the 99% confidence interval of the experimental values. This demonstrated that the modified model can accurately predict nutrient retention during thermal processing of products packed in cylindrical containers, and placed in horizontal position.

Food Technology↗
PubMed1995

Cell type differences in Golgi retention signals for transmembrane proteins.

The transmembrane domain of Golgi resident proteins such as beta-galactoside alpha 2,6-sialyltransferase (ST) and N-acetylglucosaminyltransferase 1 (NT) contain a Golgi retention signal which confers Golgi retention to reporter proteins appended to them in the appropriate context. Thus, chimeras of the cell surface protein dipeptidyl peptidase IV containing the transmembrane domain of ST and NT are retained in the Golgi apparatus in MDCK and COS cells, as assessed by indirect immunofluorescence microscopy. Transfection of these chimeric constructs into CHO cells, however, results in their transport to vesicular structures which do not colocalize with that of an endogenous Golgi marker, mannosidase II. Furthermore, the staining pattern of these structures are not affected by brefeldin A. Biochemical analysis of the transgene products in pulse-chase experiments revealed that the chimeric proteins eventually become resistant to endoglycosidase H, suggesting that they are transported beyond the medial Golgi and therefore the vesicular structures are likely to be post-Golgi. The vesicular structures colocalized well with a lysosomal marker, cathepsin D, and also with internalized FITC-dextran chased into the lysosomal compartment. Monitoring the cell surface appearance of the chimeric protein suggests that the majority is transported directly to the lysosomal compartment. Golgi retention can be completely restored for ST and improved for NT by the inclusion of sequences flanking the transmembrane domain. Our results reflect cell type differences in the interpretation of the transmembrane domain Golgi retention signal, established that general Golgi retention of type II glycosyltransferases requires the hydrophilic flanking sequence as well as the transmembrane domain, and demonstrate that proteins which escape Golgi retention may be channeled to the lysosomal pathway.

Animals↗
PubMedDate not supplied

Mechanical evaluation of craniofacial osseointegration retention systems.

This study evaluates mechanical behavior of retention systems that have been used in craniofacial osseointegration. A loading/measuring apparatus was custom designed and constructed. Test bases that represented a typical auricular situation were constructed. These bases allowed for three points of retention. Jigs that could be reproducibly positioned carried the reciprocal portion of the retentive components. The test apparatus provided vertical and horizontal loads in five locations. The system was used to test two ball-and-socket attachments (Dalla Bona; Nobelpharma), cast and preformed bar and clips (Nobelpharma), and three magnet systems (Dynamag; Neomag; Technovent). The loading/measuring apparatus was also used to evaluate the performance of two facial prosthetic adhesives. Retention systems employed in craniofacial osseointegration offer more predictable retention than the facial prosthetic adhesives. The mechanical retention systems are best suited to situations where tensile and shear forces will operate. Magnet systems are best used where only tensile forces are anticipated or where horizontal forces on the implants are to be avoided.

Adhesives↗
PubMed1995

Entorhinal-hippocampal connections and object memory in the rat: acquisition versus retention.

Investigations of the neurobiology of memory using experimental animals have modeled many of the characteristic features of amnesia seen in human clinical populations. To examine long-term memory, however, animal models of amnesia often employ extended measures of acquisition, which stand in contrast to the retention measures used with humans. To determine the role of entorhinal-hippocampal circuitry on both information acquisition and long-term retention, rats with bilateral transections of the angular bundle were trained on three object discrimination problems and then retrained two weeks later to measure retention. Animals with discrete lesions of the angular bundle, which disrupted perforant path connections from the entorhinal cortex to the hippocampus and efferent hippocampal-cortical projections, acquired the object discrimination problems normally but showed a marked deficit in retention. These findings are important because they indicate that the role of entorhinal-hippocampal connections may be limited to maintaining some types of information (e.g., single object discriminations) for retention. This dissociation, moreover, suggests that behavioral paradigms that include a measure of retention may be particularly important for characterizing the mnemonic functions of the hippocampal/parahippocampal region.

Amnesia↗
PubMed1994

Medical education and the retention of rural physicians.

OBJECTIVE: This study inquires whether retention in rural practice settings is longer for graduates of public medical schools and community hospital-based residencies, and for those who participated in rural rotations as medical students and residents. These questions are addressed separately for "mainstream" rural physicians and physicians serving in the National Health Service Corps (NHSC). DESIGN: Design is a prospective cohort study. PARTICIPANTS: Study subjects were 202 primary care physicians who graduated from U.S. allopathic medical schools from 1970-1980, and who in 1981 were working in a nationally representative sample of externally subsidized rural practices. Nearly half were serving in the NHSC. Physicians were first identified in 1981 as part of an earlier study. INTERVENTION: In 1990, study subjects were re-located and sent a follow-up mail survey inquiring about their medical training backgrounds and their careers from the time of graduation until 1990. We examined associations between four features of physicians' medical training and their subsequent retention in rural practice settings. RESULTS: Among those not in the NHSC, rural retention duration did not differ for those from public versus private medical schools, those who trained in community hospitals versus university hospital-based residencies, or for those who completed versus did not complete rural rotations as students or residents. Among NHSC physicians, no retention duration differences were noted for those with rural experiences as students or residents, or for those trained in community hospital residencies. Contrary to common wisdom, public school graduates in the NHSC remained in rural areas for shorter periods than private school graduates. CONCLUSIONS: These findings call into question whether current rural-focused medical education initiatives prepare rural physicians in ways able to influence their retention in rural settings. For purposes of enhancing the rural practice retention of its alumni, the NHSC should not selectively award scholarships to students from public medical schools.

Adult↗
PubMed1994

Characterization of the retention motif in the C-terminal part of the long splice form of platelet-derived growth factor A-chain.

Platelet-derived growth factor (PDGF) A-chain is found in two different splice variants; the long A-chain variant differs from the short one in that it contains a stretch of basic amino acid residues in the C-terminal part that mediates retention of the growth factor inside the producer cell and to the cell matrix. By analyzing mutants in which different amino acid residues in the retention motif had been changed to alanine residues, we found that the total positive charge of the sequence is of importance for the function of the retention motif. Moreover, we showed that retention also occurs if only one of the polypeptides in the PDGF dimer carries the retention motif. Surface iodination and competition with a peptide having the sequence of the retention motif revealed that the long A-chain variant, in contrast to the short A-chain variant, is localized on the outside of the cells and is also associated to the cell matrix. The association is likely to be mediated partially through heparan sulfate proteoglycans since treatment of matrix with heparitinase released the long A-chain variant.

Alternative Splicing↗