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PubMed1980

Effects of substantia nigra lesions on forebrain 2-deoxyglucose retention in the rat.

A method was developed for the measurement of regional 2-deoxyglucose (2-DG) retention in rat brain by injecting tracer quantities of tritated 2-DG intravenously, dissecting out individual brain regions, making extracts of the tissue, and counting aliquots of the extracts. This technique permits the separation of unreacted 2-DG from 2-deoxyglucose-6-phosphate (2-DGP) by ion exchange chromatography as well as the performance of other biochemical measurements on the extracts. Using this method, the effect of unilateral 6-hydroxydopamine (6-OHDA) lesions of the substantia nigra on 2-DG retention and 2-DGP formation by the striatum and the cerebral cortex was investigated. Animals were studied both 3 days and 2--4 weeks after lesioning. The location and efficacy of the lesions were verified histologically, behaviorally (by observing rotational behavior), and biochemically (by assay of striatal dopamine concentration or tyrosine hydroxylase activity). The lesions induced a mean asymmetry of less than 10% in 2-DG retention and in 2-DGP formation in striatum and cerebral cortex. This result was verified by [14C]2-DG autoradiography. Systemic administration of amphetamine (5 mg/kg) or apomorphine HBr (1.5 mg/kg) elicited rotational behavior, but did not induce a marked asymmetry of 2-DG retention in the regions studied. It is concluded that unilateral lesions of the nigrostriatal dopaminergic pathway have, at most, a modest effect on 2-DG retention by forebrain structures. We also conclude that vehicle injections may produce morphological and chemical evidence of brain injury, including small but reproducible changes in deoxyglucose retention.

Animals↗
PubMed1994

Posttraining infusion of lidocaine into the amygdala basolateral complex impairs retention of inhibitory avoidance training.

The present experiment examined the role of the central nucleus and basolateral complex in the retention of inhibitory avoidance training by reversibly inactivating these regions with lidocaine immediately following training. Male Sprague-Dawley rats were surgically implanted bilaterally with cannulae aimed at the central nucleus or the basolateral complex. One week later, they received one trial inhibitory avoidance training (0.45 mA; 1 s), followed immediately by infusions of lidocaine hydrochloride or buffer (10 micrograms/0.25 microliters). Retention was tested 2 days after training. Immediate posttraining infusions of lidocaine into the central nucleus did not affect retention performance; in contrast, immediate posttraining infusions of lidocaine into the basolateral complex significantly impaired retention performance. In addition, the effect of posttraining infusions of lidocaine into the basolateral complex was time-dependent: infusions administered 6 h after training also impaired memory, but infusions administered 24 h after training had no effect. Immediate posttraining infusions of lidocaine also impaired the retention performance of rats trained with a more intense footshock (0.75 mA). However, at the higher footshock intensity, administration of lidocaine 6 h after training had no effect on retention performance. The time- and footshock-dependent retrograde impairment of memory produced by posttraining reversible inactivation of the basolateral complex suggests that this region of the amygdala is involved in the consolidation of memory for inhibitory avoidance training.

Amygdala↗
PubMed1992

Prediction of peptide retention time in reversed-phase high-performance liquid chromatography.

Peptide retention in reversed-phase chromatography depends mainly on the amino acid composition of peptides and can therefore be predicted by summing the relative hydrophobic contributions of each constitutive amino acid residue. The prediction is correct for small peptides but overestimates the retention times of peptides larger than 10-15 residues. A new prediction model is proposed in which the contribution to peptide retention of each amino acid residue is not a constant but a decreasing function of peptide length. From the retention times of 104 peptides, the parameters of decreasing functions were estimated by a non-linear multiple regression analysis. The contribution to peptide retention of charged, polar and non-polar residues appears to be differently affected by peptide length. The secondary structure of most peptides during reversed-phase high-performance liquid chromatography could be responsible for this. The high correlation between the predicted and observed retention times of peptides which were not used to establish the model indicates a good predictive accuracy of the new model.

Amino Acid Sequence↗
PubMed1996

Structure-retention relationships of steroid hormones in reversed-phase liquid chromatography and micellar electrokinetic capillary chromatography.

Quantitative structure-retention relationship (QSRR) studies are useful in retention prediction, finding the relevant structural descriptors for analytes and estimating the relative biological activities of a series of analytes. Most of the studies have been conducted by RP-HPLC and a few by micellar electrokinetic capillary chromatography (MECC). The aim of this work was to find structural parameters and characteristics related to the RP retention and electrophoretic migration of steroids in order to predict the retention/migration of steroid hormones on the basis of their molecular structure. Retention data were obtained with an ODS column using a mobile phases aqueous methanol-acetonitrile (mobile phase A) and methanol-tetrahydrofuran (mobile phase B). MECC was conducted with a sodium dodecyl sulfate (SDS)-borate system and with a mixed micellar solution of SDS and sodium cholate. Several topological indices, such as the connectivity indices, chi, were used as structural parameters. Steric factors seem to have a great effect on the retention of steroid hormones, especially with the MeCN-containing mobile phase. Retention in mobile phase B could be predicted more accurately. Topological indices can be used in the modelling and prediction of the retention/migration of steroid hormones when the solutes form a congeneric series and stereochemical properties do not govern the separation process.

Chromatography↗
PubMed1996

Use of principal component analysis for the study of the retention behaviour of anticancer drugs on a beta-cyclodextrin polymer-coated silica column.

The retention parameters of eighteen commercial anticancer drugs were determined on a beta-cyclodextrin polymer-coated silica support (beta CDP) using methanol-water mixtures as eluent and the relationship between the retention behaviour and physico-chemical parameters was elucidated by principal component analysis (PCA) followed by two-dimensional non-linear mapping. No significant linear correlation was found between the retention behaviour of drugs on octadecylsilica and beta CDP silica columns, indicating that the retention capacity and selectivity of the columns are considerably different. The results of PCA indicated that hydrophobic and electronic interactions and steric conditions govern the retention of anticancer drugs on beta CDP column, suggesting a mixed retention mechanism.

Antineoplastic Agents↗
PubMed1984

The effect of a corrugated channel on the retentive properties of an obturator-reinforced composite resin dowel-core system.

A study was conducted to compare the retentive properties of the obturator-reinforced composite resin dowel and core systems with and without corrugated dentin surfaces in the dowel channels. A commercially available tap with a diameter of about 1.4 mm and a thread groove depth of 100 micron was used to accomplish this dentin roughening. To compare whether methods of placement affect the retentive capacities of this dowel and core system, a Lentulo spiral, Jiffy tube, and Centrix C-R syringe were used to insert the resin mixes into the corrugated channels. The following conclusions can be drawn. By corrugating or roughening the dentin surface of the prepared channel, the retentive properties of this dowel and core system are significantly increased. In this system using minimal amounts of composite resin, the three methods of placement exhibited no significant difference in retention. The retentive failure seemed to occur at the resin-tooth interface. Increasing the degree of corrugation (deeper grooves) increased the retention, but caution must be exercised to prevent weakening the tooth.

Crowns↗
PubMed1985

Iron retention and distribution in the cadmium-induced iron deficiency.

The retention and distribution of iron-59 after oral administration of a single iron dose in the presence and absence of various cadmium doses were tested in normal rats acutely or subchronically treated with various amounts of dietary cadmium (28, 56, 112 ppm). In a second series of experiments the kinetic parameters (Km and Vmax) of iron absorption were estimated in normal and iron-deficient rats after oral administration and from tied-off jejunal and duodenal segments. In acute experiments the retention of iron decreased inversely with respect to the cadmium dose administered simultaneously. After subchronic exposure to dietary cadmium for 4 weeks the retention of iron was increased if iron was administered alone or together with cadmium in comparison to normal controls. If iron was administered alone to subchronically treated animals, iron retention was of the same order of magnitude as in iron-deficient controls. However, if iron was administered together with cadmium (molar ratios 1/0.5, 1/1, 1/2 mumol/kg body wt) the retention of iron was decreased in a dose-dependent manner. The iron content in the liver and spleen of acutely exposed rats decreased, whereas the tissue content of the treated rats increased according to the increased body retention of iron. The utilization of iron for hemoglobin synthesis remained unchanged in all groups investigated.

Anemia, Hypochromic↗
PubMed1990

Retention of cadmium in cadmium-naive normal and iron-deficient rats as well as in cadmium-induced iron-deficient animals.

The retention of cadmium was investigated in cadmium-naive normal and iron-deficient rats in comparison to rats with cadmium-induced iron deficiency. Rats subchronically (4 weeks) exposed to dietary cadmium (28, 56, 112 ppm Cd and 28 ppm Fe) received a radioactively labeled dose of 2 mumol Cd/kg body wt; acutely (no cadmium exposure with diet) treated rats received doses between 1 and 8 mumol Cd/kg body wt. Two animals of each group received iron (1 mumol/kg as 59FeSO4 in order to monitor iron absorption in parallel. After a period of 4 weeks of feeding a cadmium-fortified diet, the test dose was administered and after a 2-weeks period 109Cd and of 59Fe retention was determined. The results showed in part an unexpected pattern of cadmium retention: subchronic feeding of cadmium induced iron deficiency. This implies an immediate interaction between the two metals with regard to intestinal transfer of iron. The retention of iron was increased in the Cd-induced anemia to the same extent as that in iron deficiency induced by iron restriction. Cadmium retention in iron deficiency induced by iron withdrawal also showed a marked increase, which implies that iron deficiency stimulates the intestinal transfer system for both metals in a similar way. Contrary to this effect, the cadmium retention in cadmium-induced iron deficiency was reduced to about 30% of control values. A self-induced aggravation of the body cadmium burden, as a consequence of the iron deficiency which is known to result from subchronic exposure to feeding of dietary cadmium, was thus excluded.

Anemia, Hypochromic↗
PubMedDate not supplied

Cholecystokinin receptors mediate enhanced memory retention produced by feeding and gastrointestinal peptides.

Ingestion of food in mice following training on T-maze footshock avoidance enhanced memory retention when tested 7 days later. This eating-induced improvement of retention was blocked by a specific cholecystokinin antagonist, L-364,718. The cholecystokinin antagonist prevented enhancement of memory retention resulting from posttraining administration of the gastrointestinal hormones, cholecystokinin, bombesin or gastrin releasing peptide. L-364,718 neither impaired or improved retention when given alone. Specificity of the effect of L-364,718 was demonstrated by the failure of L-364,718 to block improved memory retention resulting from administration of arecoline and D-amphetamine. The studies provide evidence that activation of cholecystokinin receptors plays a physiological role in the mediation of meal-induced enhancement of memory retention.

Animals↗
PubMed1990

The effect of the lecture discussion teaching method with and without audio-visual augmentation on immediate and retention learning.

This study determined whether students taught using the lecture-discussion method augmented with audio-visuals would achieve a higher mean score on an immediate post-test and delayed retention test than students presented with a lecture-discussion without audio-visuals. A convenience sample of 52 students divided into two groups voluntarily participated in the quasi-experiment. Two teaching sessions averaging 90 minutes in length were taught by the researcher. Learning and retention were measured by a 10-item multiple choice test with content validity. Immediate learning was measured with a post-test administered immediately following each of the teaching sessions. Delayed learning was measured with a retention test administered 25.5 days following the teaching sessions. Group data was analysed using an independent one tailed t-test for mean scores. Students attending the lecture-discussion with audio-visual augmentation did not achieve significantly higher mean scores on the two tests than the non-augmented group (p less than or equal to 0.05). Analysis using a paired t-test revealed that the difference in scores between the post-test and retention test for the group without audio-visual augmentation was significant (t = 2.31; p less than 0.05). Delayed retention appears to have been influenced by the use of audio-visuals. Nurse educators need to consider ways in which the lecture-discussion may be enhanced to maximise student learning and retention.

Audiovisual Aids↗
PubMed1995

Analysis of zeins' ER retention in Xenopus oocytes.

Zeins, maize storage proteins, are retained in the endoplasmic reticulum (ER) during the intracellular protein targeting process. Hydrophobic interaction has been postulated as the driving force of zeins' aggregation and retention in the ER. Recently, a class of zein (the 27K zein) has been proposed to facilitate zeins' ER retention by anchoring to the ER membrane. This study investigated the significance of the two proposed mechanisms toward zeins' ER retention using Xenopus oocyte. Following injection of the total or 27K zein mRNA, zein's movement within the ER was analyzed based upon the extent of diffusion to the non-injected oocyte half. This study indicates that the total zeins freely move within the lumen of the ER, thus, suggesting that the intermolecular aggregation, leading to insolubility and exclusion from the ER lumenal fluid, may not be essential for zeins' ER retention. This study also suggests that the 27K zein may not facilitate zeins' ER retention by virtue of an anchor to the ER membrane based on its free movement in the ER. Free movement of the total and 27K zeins, under conditions where zein aggregates should form, necessitates a reevaluation of the mechanisms responsible for zein polypeptides' ER retention and protein body formation.

Animals↗
PubMed1986

The 4 h/24 h 99mTc-MDP whole body retention: a new index of bone pathology.

A simple technique for determining the whole body retention of 99mTc labeled methylene diphosphonate (MDP) at 4-h and 24-h was applied to 28 adult patients (22 prostate cancer, 6 osteoporosis). Following administration of 20 mCi (740 MBq) 99mTc-MDP, a qualitative scintigram was performed and whole body retention was recorded at 4 and 24 h. The prostate cancer patients all had positive bone scintigrams, and of this group, 7 were in relapse and 15 in remission on chemotherapy. The osteoporotic groups whole body retention values were determined prior to the initiation of drug therapy. Mean percent whole body retention values were significantly greater at 4 and 24 h for the cancer patients in relapse relative to both the prostate cancer patients in remission and the osteoporotics: 4-h%/24-h%; equals 74.3/60.2, 57.5/33.5, and 48.0/30.3, respectively. The whole body retention values of the latter two groups, however, were only significantly different at 4-h. An additional index of skeletal pathology was developed by combining the 4-h/24-h values to calculate the biological half time (t1/2b) for this time period using a single exponential model. Again the cancer patients in relapse exhibited a significantly longer half time relative to those in remission and the osteoporotics (70.4 vs 25.7 h and 29.2 h, respectively). The combination of 4 and 24-h whole body retention values with the associated t1/2b has potential for following and classifying patients during the course of their skeletal disease. These values have been shown to be especially valuable with cancer patients with metastatic disease.

Bone Neoplasms↗
PubMed2004

Factors affecting retention of early pregnancy in dairy cattle.

Potential factors affecting retention of pregnancy during weeks 5-9 of gestation were studied in dairy cows and heifers (N = 211) on two farms. Cows were examined by ultrasonography for presence of a viable embryo, and sizes of the corpus luteum (CL) and of follicles > or = 5mm were recorded. Blood samples were taken at each examination and assayed for progesterone and estradiol. Overall pregnancy loss was 11.4%. Cows with two CL did not have greater concentrations of progesterone than cows with one CL and they retained fewer pregnancies (P < 0.01; 73% versus 91%). Pregnancy retention was associated positively with concentrations of progesterone and estradiol during week 5 (P < 0.05). Embryos that were lost apparently died before CL regression. Retention of pregnancy declined in cows with high body condition and as age of the cow increased. Pregnancy retention was lower in cows bred to one of four frequently-used service sires (P < 0.05). Days postpartum, milk production, parity, service number, inseminator, synchronization of estrus, diameter of follicles and size of CL did not affect pregnancy retention. In conclusion, retention of pregnancy during placentation varied with concentrations of progesterone and estradiol, age of cow, body condition and service sire.

Abortion, Veterinary↗
PubMed2004

Intake, ingesta retention, particle size distribution and digestibility in the hippopotamidae.

Although several aspects of the digestive physiology of the hippopotamidae-non-ruminating foregut fermenters-have been described, ingesta kinetics and passage characteristics of these species are not well understood. The most outstanding feature of the hippo digestive physiology reported so far is the very long mean ingesta retention times (MRTs) measured by Foose [Foose, T., 1982. Trophic strategies of ruminant versus nonruminant ungulates. PhD dissertation, University of Chicago, Chicago.]. Since those data had been investigated with animals without water access, we intended to measure MRT in hippos which were allowed to enter water pools during the night. MRT parameters as well as dry matter (DM) digestibility were determined in four common (Hippopotamus amphibius) and four pygmy hippos (Hexaprotodon liberiensis) on two different diets each using cobalt ethylendiamintetraacetate (Co-EDTA) as a fluid, chromium (Cr)-mordanted fibre (<2 mm) as a particle and acid detergent lignin (ADL) as an internal digestibility marker. Four of the animals additionally received cerium (Ce)-mordanted fibres (2-10 mm) as particle markers. Total MRTs for fluids and particles ranged between 20-35 and 48-106 h in the common and between 13-39 and 32-107 h in the pygmy hippos. The difference between fluid and particle retention was greater than usually reported in ruminants. Excretion patterns of the markers differed from those usually observed in ruminants but resembled those reported for macropods (kangaroos), indicating a plug-flow reactor-like physiology in the hippo forestomach (FRST). This finding complements other described similarities between the macropod and the hippo forestomach. The measurements of larger particle retention profiles suggest that in the hippo, larger particles might be excreted either faster or at the same rate as smaller particles, indicating a general difference between ruminants and hippos with respect to differential particle retention. The digestive physiology of hippos is characterised by a generally low food intake, long ingesta retention times and dry matter digestibilities lower than reported in ruminants. Moderate digestibilities in spite of long retention times might be the result of the generally high average ingesta particle size in hippos. The comparatively easy management of pygmy hippos, together with the significant correlations between food intake, MRT and digestibility in the pygmy hippos of this study, recommends this species for further studies on the interplay of these parameters in herbivore digestive physiology.

Animals↗
PubMed2005

Fluid and particle retention in captive okapi (Okapia johnstoni).

Retention time of food in the digestive tract is among the key variables that describe the digestive strategy of a herbivore. Mean retention time (MRT) was measured on 4 captive specimens of the okapi, a strictly browsing ruminant. Retention time was quantified on different diets, using Co-EDTA (fluid phase) and Cr-mordanted fibres (1-2 mm) (particle phase) as pulse-fed markers. Average food intake was 55-65 g DM/(kg BW0.75*d). Fecal excretion of the markers was quantified over 10 days. Different models to calculate retention time and passage rate in the gastrointestinal tract (GIT) and the reticulorumen (RR) were applied. Average MRT(particle)GIT was quantified to be 47+/-8 h and MRT(fluid)GIT 36+/-5 h. Concerning estimation of retention times in the reticulorumen, MRT(particle)RR was quantified to be 27+/-7 h, while MRT(fluid)RR was 17+/-4 h. The quotients MRT(particle)/MRT(fluid) were quantified to be 1.3+/-0.1 for the GIT and 1.6+/-0.2 for the RR. Compared to data established with comparable markers, the okapi has low coefficients of MRT(particle)/MRT(fluid). A less well developed retention mechanism for fibres compared to species like cattle or sheep can be explained by a comparatively high fermentation rate and low digestibility of the natural food of the okapi-browse-in comparison to grass.

Animals↗
PubMed2004

Evaluation of a structure-driven retention model for temperature-programmed gas chromatography.

The solvation parameter model is suitable for describing the retention properties of compounds of varied structure in temperature-programmed gas chromatography. An empirical second-order model provides a good account of the change in system constants as a function of program rate. These relationships codify the reduction in retention time at higher program rates and changes in elution order (selectivity) with program rate. The prediction of retention times from structure, while quite good, is probably adversely affected by descriptor quality and the possibility of a mixed retention mechanism on polar stationary phases. Plots of experimental against predicted temperature-programmed retention times for varied compounds are linear but generally contain a small bias from an ideal model (slope of one and an intercept of zero). The average absolute deviation in temperature-programmed retention times on three columns (DB-210, DB-1701 and EC-Wax) varied from 0.15 to 0.89 min with the best results obtained at higher program rates on the columns of lower polarity.

Chromatography, Gas↗
PubMed2004

New insights on the retention mechanism of non-polar solutes in reversed-phase liquid chromatographic columns.

A clarification of the retention mechanism of non-polar solutes in octadecyl reversed-phase chromatographic columns is attempted based on a systematic comparison of the retention in C18 and C2 columns under the assumption that the retention in C2 columns is due to adsorption. The comparison involves curve fitting procedures and tests based on the properties of special functions suggested in the present paper. For the application of this approach the retention behaviour of six non-polar solutes, benzene, toluene, ethylbenzene, propylbenzene, isopropylbenzene and tert-butylbenzene, is studied from aqueous mobile phases modified with methanol, isopropanol, acetonitrile and tetrahydrofuran using C18 and C2 reversed-phase columns. It was found that the retention mechanism in C18 columns is not the same in the four modifiers. In particular, our results show that the adsorption mechanism has a significant contribution in mobile phases modified by acetonitrile and tetrahydrofuran, the partition mechanism is likely to predominate in isopropanol-water mobile phases provided that the mole fraction of isopropanol is higher than 0.2, whereas the case of MeOH is rather obscure, since the various tests did not give a clear picture about the retention mechanism in methanol-water mobile phases.

Chromatography, Liquid↗
PubMed2004

Effect of temperature on the chromatographic retention of ionizable compounds. I. Methanol-water mobile phases.

The retention mechanism of acids and bases in reversed-phase liquid chromatography (RPLC) has been experimentally studied by examining the temperature dependence of retention, with emphasis on the role of the buffer ionization equilibria in the retention and selectivity. Retention factors of several ionizable compounds in a typical octadecylsilica column and using buffers dissolved in 50% (w/w) methanol as eluents at three temperatures in the range of 25-50 degrees C were measured. Two pairs of buffer solutions were prepared by a close adjusting of their pH at 25 degrees C; differences in their ionization enthalpies determined a different degree of ionization when temperature was raised and, as a consequence, a different shift in the eluent pH. Predictive equations of retention that take into account the temperature effect on both the transfer and the ionization processes are proposed. This study demonstrates the significant role that the selected buffer would have in retention and selectivity in RPLC at temperatures higher than 25 degrees C, particularly for co-eluted solutes.

Acids↗