PubMed Health⌕ Search

SEARCH · PubMed Health

Results for “Scintillation Counting”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 955 records · Page 53Linked to original sources
PubMed1991

In vitro studies on drug interaction of ifosfamide and ACNU in primary and metastatic human brain tumours.

Combination chemotherapy is widely employed in clinical oncology; however, there is no generally accepted model to evaluate individual tumour susceptibility to a given drug combination protocol. We therefore investigated the drug interaction of ifosfamide (4-hydroxyperoxy-ifosfamide) and ACNU in a recently developed in vitro model of paired sequential combination chemotherapy in primary and metastatic malignant brain tumours. A long-term standard [6,3-3H]-thymidine-incorporation assay, employing a liquid scintillation counting protocol, was selected to assess the drug sensitivity of human tumours. In vitro drug exposures were derived from correlating in vivo-(systemic and CNS) and in vitro-pharmacokinetic drug parameters. In combination experiments tumour cells were treated sequentially by two drugs in both sequences: drug exposures were calculated for 2 h with a 1-h drug-free interval in between. "Cut-off" concentrations (maximum in vitro exposure doses) were calculated as 1.74 microM (for primary CNS tumours: 0.58 microM) for ifosfamide and 5.4 microM (for primary CNS tumours: 1.33 microM) for ACNU. Dose/response relations were derived from isotope incorporation rates after cells had grown for approximately five population doubling times. Combination isoboles were plotted after drug doses had been transformed into "equieffective doses", enabling comparison of drug combination effects. In all three glioblastomas (with CNS exposure dose) an additive or supra-additive effect could be observed in either sequence (in one tumour a biphasic additive isobole was found for both sequences). Out of three bronchial carcinomas (small-cell type, brain metastases) in two non-identical sequences a supra-additive effect was observed in two tumours, with antagonistic effects in the third tumour. In all three malignant melanomas and in one renal carcinoma antagonistic effects were observed, whereas in a second renal carcinoma supra-additive effects were demonstrated for both sequences. We conclude that drug combination chemotherapy effects at the cellular level may be extremely heterogeneous.

Antineoplastic Combined Chemotherapy Protocols↗
PubMed1976

Studies on the brush border membrane of mouse duodenum. III. Iodination of membrane proteins.

Microvillus membranes were iodinated from luminally administered lactoperoxidase, H2O2 and 125I before and after neuraminidase treatment. Membranes were isolated, solubilized in sodium dodecyl sulphate buffer and electrophoresed on gels. Gels were stained for protein, and then sliced for liquid scintillation counting. When membranes were not treated with neuraminidase, the nonpermeating iodination probe attached only to a band containing protein of 150,000 daltons approximate molecular weight. This size class of protein may reside on the luminal side of the brush border membrane as opposed to the serosol side. Qualifications of this statement are discussed with reference to the location of tyrosyl residues and to the possibilities of masking molecules. Membranes treated from the luminal side with neuraminidase to remove possibly masking carbohydrate and then iodinated, appeared to contain an additional protein of estimated molecular weight 220,000 daltons which was accessible to 125I. Thus, a 220,000 dalton protein may also be on the luminal side of the membrane. An explanation is attempted for the discrepancy between the very few proteins labelled and the many proteins involved in terminal digestion and transport which would all be expected to be available to luminally administered iodination probe. Membranes were isolated, exposed to iodination and then solubilized for electrophoresis. Nearly all proteins were labelled, which indicated that there is an asymmetric distribution of proteins in the plane of the membrane. The two smallest molecular weight polypeptides which were not iodinated were proposed to be so disposed in the membrane that they were inaccessible to the probe, from either side.

Animals↗
PubMed1979

Binding of radioactively labeled saxitoxin to the squid giant axon.

The binding of saxitoxin, a specific inhibitor of the sodium conductance in excitable membranes, has been measured in giant axons from the squid, Loligo pealei. Binding was studied by labeling saxitoxin with tritium, using a solvent-exchange technique, and measuring the toxin uptake by liquid scintillation counting. Total toxin binding is the sum of a saturable, hyperbolic binding component, with a dissociation constant at 2--4 degrees C of 4.3 +/- 1.7 nM (mean SE), and a linear, nonsaturable component. The density of saturable binding sites is 166 +/- 20.4 micrometers-2. From this density and published values of the maximum sodium conductance, the conductance per toxin site is estimated to be about 7 pS, assuming sequential activation and inactivation processes (F. Bezanilla & C.M. Armstrong, 1977, J. Gen. Physiol. 70:549). This single site conductance value of 7 pS is in close aggreement with estimates of the conductance of one open sodium channel from measurements of gating currents and of noise on squid giant axons and is consistent with the hypothesis that one saxitoxin molecule binds to one sodium channel.

Animals↗
PubMed1983

Na+, Li+, and Cl- transport by brush border membranes from rabbit jejunum.

Na+, Li+, K+, Rb+, Br-, Cl- and SO4(2-) transport were studied in brush border membrane vesicles isolated from rabbit jejunum. Li+ uptakes were measured by flameless atomic absorption spectroscopy, and all others were measured using isotopic flux and liquid scintillation counting. All uptakes were performed with a rapid filtration procedure. A method is presented for separating various components of ion uptake: 1) passive diffusion, 2) mediated transport and 3) binding. It was concluded that a Na+/H+ exchange mechanism exists in the jejunal brush border. The exchanger was inhibited with 300 microM amiloride or harmaline. The kinetic parameters for sodium transport by this mechanism depend on the pH of the intravesicular solution. The application of a pH gradient (pHin = 5.5, pHout = 7.5) causes an increase in Jmax (50 to 125 pmol/mg protein . sec) with no change in Kt (congruent to 4.5 nM). Competition experiments show that other monovalent cations, e.g. Li+ and NH4+, share the Na+/H+ exchanger. This was confirmed with direct measurements of Li+ uptakes. Saturable uptake mechanisms were also observed for K+, Rb+ and SO4(2-), but not for Br-. The Jmax for K+ and Rb+ are similar to the Jmax for Na+, suggesting that they may share a transporter. The SO4(2-) system appears to be a Na+/SO4(2-) cotransport system. There does not appear to be either a Cl-/OH- transport mechanism of the type observed in ileum or a specific Na+/Cl- symporter.

Amiloride↗
PubMed1980

Bio-distribution in rats of some salicylates with low gastric ulcerogenicity.

The distribution of three radioactively labelled salicylate derivatives with low ulcerogenic activity was compared with that of acetylsalicylic acid (ASA) and salicylic acid using whole body autoradiography and liquid scintillation counting techniques in rats. The methyl ester of ASA (AME) was distributed in vivo very similarly to that observed with ASA and salicylic acid. AME is rapidly demethylated following absorption from the stomach and is subsequently converted to ASA and salicylate. Salicylate is the main metabolite produced from both AME and ASA, which specifically accumulates in inflamed tissues. The 3-methyl- and 6-methyl-substituted salicylic acids are not as rapidly absorbed as either ASA or salicylic acid and do not pass readily into the brain or bone marrow. These results show that the methyl (ester) group of AME (which adequately protects the gastric mucosa from damage caused by ASA itself) does not impair the quantity of pharmacologically active form of drug (salicylate and ASA) generated in vivo. However, insertion of the methyl group at the 3- and 6-position of salicylic acid markedly affects both absorption, distribution and pharmaco-activity of these acids.

Animals↗
PubMed1984

Tissue distribution and pharmacokinetics of 3H-butylated hydroxyanisole in female mice.

Butylated hydroxyanisole (BHA), a commonly used food additive, is a phenolic antioxidant. While metabolism of BHA has been studied in dog, man, rabbit and rat, information on tissue distribution is limited to rat and dog. Time dependent distribution and elimination of 3H-BHA following a single oral dose of 50 mg/kg body weight in female Swiss-Webster mice were investigated. Animals were sacrificed at time intervals up to 168 h after dosing. Levels of 3H were determined by liquid scintillation counting in the following tissues: brain, blood, serum, fat, heart, kidney, liver, lung, skeletal muscle and spleen. In most tissues the decline of BHA (log) was nonlinear with respect to time; a biphasic, post-absorptive aspect was observed. The highest 3H activity was noted in kidney and liver 15 min after dosing. The lowest activity was in fat. In addition, a peak 3H activity was recorded at 3 and 10 h after dosing for the blood and brain, respectively. Distribution of the 3H-BHA in mouse organs is similar to that in rat.

Animals↗
PubMed1990

Pharmacokinetics and metabolism of a single subneurotoxic oral dose of tri-o-cresyl phosphate in hens.

Hens were given a single oral dose of 50 mg (4.6 microCi)/kg [14C] tri-o-cresyl phosphate (TOCP). Four groups of three hens each were killed after 0.5, 1, 2, and 5 days. The half-life of 14C in plasma was 2 days. TOCP and its metabolites in the plasma, liver, kidneys, and lungs were analyzed by high-performance liquid chromatography and liquid scintillation counting. TOCP reached its highest concentration in plasma between 0.5 and 1 day after administration. Under these experimental conditions, the disappearance of TOCP from the plasma followed monoexponential kinetics with a half-life of 2.2 days. Appreciable concentrations of saligenin cyclic-o-tolyl phosphate, the active neurotoxic metabolite, were detected in the plasma as well as in the liver, kidneys, and lungs at all time points and had half-lives of 2.06, 1.36, 1.11 and 4.44 days, respectively. The presence of this active metabolite of TOCP might contribute to the sensitivity of the hen to TOCP-induced delayed neurotoxicity. Other hydrolytic and oxidative products of TOCP were also identified in tissues.

Administration, Oral↗
PubMed1994

Regional brain distribution of risperidone and its active metabolite 9-hydroxy-risperidone in the rat.

Risperidone is a new benzisoxazole antipsychotic. 9-Hydroxy-risperidone is the major plasma metabolite of risperidone. The pharmacological properties of 9-hydroxy-risperidone were studied and appeared to be comparable to those of risperidone itself, both in respect of the profile of interactions with various neurotransmitters and its potency, activity, and onset and duration of action. The absorption, plasma levels and regional brain distribution of risperidone, metabolically formed 9-hydroxy-risperidone and total radioactivity were studied in the male Wistar rat after single subcutaneous administration of radiolabelled risperidone at 0.02 mg/kg. Concentrations were determined by HPLC separation, and off-line determination of the radioactivity with liquid scintillation counting. Risperidone was well absorbed. Maximum plasma concentrations were reached at 0.5-1 h after subcutaneous administration. Plasma concentrations of 9-hydroxy-risperidone were higher than those of risperidone from 2h after dosing. In plasma, the apparent elimination half-life of risperidone was 1.0 h, and mean residence times were 1.5 h for risperidone and 2.5 h for its 9-hydroxy metabolite. Plasma levels of the radioactivity increased dose proportionally between 0.02 and 1.3 mg/kg. Risperidone was rapidly distributed to brain tissues. The elimination of the radioactivity from the frontal cortex and striatum--brain regions with high concentrations of 5-HT2 or dopamine-D2 receptors--became more gradual with decreasing dose levels. After a subcutaneous dose of 0.02 mg/kg, the ED50 for central 5-HT2 antagonism in male rats, half-lives in frontal cortex and striatum were 3-4 h for risperidone, whereas mean residence times were 4-6 h for risperidone and about 12 h for 9-hydroxy-risperidone. These half-lives and mean residence times were 3-5 times longer than in plasma and in cerebellum, a region with very low concentrations of 5-HT2 and D2 receptors. Frontal cortex and striatum to plasma concentration ratios increased during the experiment. The distribution of 9-hydroxy-risperidone to the different brain regions, including frontal cortex and striatum, was more limited than that of risperidone itself. This indicated that 9-hydroxy-risperidone contributes to the in vivo activity of risperidone, but to a smaller extent than would be predicted from plasma levels. AUCs of both active compounds in frontal cortex and striatum were 10-18 times higher than those in cerebellum. No retention of metabolites other than 9-hydroxy-risperidone was observed in any of the brain regions investigated.

Animals↗
PubMed1992

Binding characteristics of ortho-toluidine to rat hemoglobin and albumin.

The binding characteristics of [14C]ortho-toluidine (OT), a suspect human carcinogen, were investigated in male Sprague-Dawley rats. Rats were administered [14C]OT i.p. at 10, 20, 40, 50, or 100 mg/kg body weight, then sacrificed at 2, 4, 8, 18, 24, 48, or 72 h, or 7, 14, or 28 days. Hemoglobin (Hb) and albumin (Alb) were isolated from blood, and OT binding was determined by liquid scintillation counting. For Alb, peak binding occurred at 50 mg/kg at the 4-h time point (15.6 ng OT/mg Alb), while for Hb peak binding was observed at 24 h at the 100 mg/kg dose (23.0 +/- 5.1 ng OT/mg Hb). OT-Alb binding was not linear; however, OT-Hb binding appeared to increase linearly in a dose-dependent manner. Biological half-lives of OT bound to Alb or Hb were observed to be 2.6 and 12.3 days, respectively, after rats were administered a single dose of [14C]OT and sacrificed after 4 h to 28 days. The effect of route of administration on OT-Hb adduct formation was investigated, and approximately a two-fold increase in radioactivity bound to Hb was observed after i.p. administration of 100 mg/kg [14C]OT versus oral intubation. Additional studies were carried out to investigate the effect of microsomal enzyme induction. An increase in OT-Hb binding was seen in rats pretreated with phenobarbital compared to rats pretreated with beta-naphthoflavone or without pretreatment; however, this increase was not statistically significant. These results suggest that OT-Hb and OT-Alb adduct formation may be a valuable biomarker for assessing workplace exposure.

Albumins↗
PubMed1994

Artificial neural networks that use single-photon emission tomography to identify patients with probable Alzheimer's disease.

Single-photon emission tomographic (SPET) images using technetium-99m labelled hexamethyl-propylene amine oxime were obtained from 97 patients diagnosed as having Alzheimer's disease, as well as from a comparison group of 64 normal subjects. Multiple linear regression was used to predict subject type (Alzheimer's vs comparison) using scintillation counts from 14 different brain regions as predictors. These results were disappointing: the regression equation accounted for only 33.5% of the variance between subjects. However, the same data were also used to train parallel distributed processing (PDP) networks of different sizes to classify subjects. In general, the PDP networks accounted for substantially more (up to 95%) of the variance in the data, and in many instances were able to distinguish perfectly between the two subjects. These results suggest two conclusions. First, SPET images do provide sufficient information to distinguish patients with Alzheimer's disease from a normal comparison group. Second, to access this diagnostic information, it appears that one must take advantage of the ability of PDP networks to detect higher-order nonlinear relationships among the predictor variables.

Aged↗
PubMed1987

Disposition of moracizine (ethmozine) in healthy subjects after oral administration of radiolabelled drug.

Moracizine (ethmozine) is a phenothiazine derivative with demonstrated antiarrhythmic activity. To characterize the pharmacokinetics and material balance relationships in humans, we have given 14C-moracizine X HCl as a single oral dose of 500 mg (50 microCi) to six healthy men. Plasma, urine, and faecal samples were collected for 7 days after administration and the concentrations of total radioactivity and intact moracizine were determined by liquid scintillation counting and HPLC, respectively. Urine and faecal recovery accounted for 95% of the administered radioactivity. Most of this radioactivity was found in the faeces (59%). Only 0.05% of the dose was recovered from urine as intact moracizine. The Cmax and AUC for moracizine equivalents of total radioactivity were 4- and 18-fold higher, respectively, than the corresponding values for intact moracizine. Additionally, both the disappearance of total radioactivity from plasma and its excretion rate into urine were slower in comparison to intact drug. Terminal t1/2 values calculated from plasma concentration-time data were 85.2 and 3.5 h for total radioactivity and intact moracizine, respectively. However, based on urinary excretion rates, the t1/2 for total radioactivity was shorter (29.3 h) while the t1/2 for intact drug was comparable (2.7 h) to the results obtained from the plasma data. The oral plasma clearance of moracizine was relatively large (2.2 l X min-1), suggesting first-pass metabolism. The estimated oral systemic availability of moracizine was 34%.

Administration, Oral↗
PubMed1983

Enhanced incorporation of exogenous arachidonic acid into phosphatidylinositol and other phospholipids during the early stages of thrombin-induced aggregation in gerbil platelets.

The degradation of platelet phospholipids via phospholipase activity is known to occur during thrombin-induced platelet aggregation. Both phosphatidylinositol and phosphatidylcholine are considered to be sources of the released arachidonic acid which becomes a substrate for prostaglandin and thromboxane A2 formation. In this work, the effect of thrombin on the incorporation of exogenous arachidonic acid into platelet membrane phospholipids was studied. Suspensions of gerbil platelets were incubated in aggregometer cuvettes with [14C] arachidonic acid in the absence or presence of thrombin, and product formation was monitored by thin layer chromatography and scintillation counting. Within 30 sec, the entry of arachidonic acid into phosphatidylinositol was increased by 165% in thrombin-stimulated platelets over controls. Under identical conditions, the incorporation into phosphatidylcholine was increased by only 57%. These results suggest that the incorporation of exogenous arachidonic acid via lysophosphatidylinositol and lysophosphatidylcholine acyltransferase activities may be intimately associated with thrombin-induced platelet aggregation in the gerbil.

Animals↗
PubMed1993

Cholesterol and 25-hydroxycholesterol retention in specimens of liver and aorta prepared for electron microscopy. II. Effect of filipin, osmium, digitonin and saponin.

Sprague-Dawley rats were injected intraperitoneally with [1 alpha, 2 alpha(n)-3H]cholesterol or 25-hydroxy-[26,27-3H]cholesterol, and one and five days later liver and aortic tissues were fixed. The extent to which these sterols were lost from the tissues during preparation for electron microscopy (EM) was examined utilizing different fixation procedures and various protective agents. Radioactive tracers, scintillation counting and standard EM techniques were used. Although most of the procedures examined caused major lipid losses, useful fixation procedures that allow retention of cholesterol or 25-hydroxy-cholesterol in liver and aortic tissues were found and are described here.

Animals↗
PubMed1979

A microtechnique for the rapid analysis of macromolecule synthesis in minicultures of mammalian cells.

A new micromethod, called the Stanzen technique, is described for the rapid determination of DNA and protein content as well as the incorporation rates of radioactively labeled precursors into macromolecules in cells growing in replica minicultures on plastic petri dishes. The procedure yielded reproducible results assaying only minimal cell numbers per sample and was applied for studying both primary or early passaged cell cultures (mouse epidermal cells and fibroblasts) and a malignantly transformed epidermal cell line. In four well defined circular areas (called Stanzen) marked on the bottom of tissue-culture plastic petri dishes (by heated stamps), 0.2 to 4 x 10(5) cells per area were plated and grown as four individual cultures in one dish. Both treatment and labeling with radioactive precursors of these Stanzen cultures were performed as with normal petri dishes. After fixation and extraction of the cultures, the singular Stanzen areas (with the cells fixed onto them) were sawed out and transferred into vials for liquid-scintillation counting or determination of DNA and protein. The obtained values of specific activity corresponded well whether the samples compared were derived from the minicultures of the same dish or from several dishes. By modifications of the known colorimetric methods for DNA and protein determination, the sensitivity of these procedures was improved down to values of 1 microgram DNA or 5 micrograms protein per individual culture. These micromodifications yielded the same values as the standard methods whether applied to cell suspensions or to cell cultures. Finally, cell proliferation was not influenced by the growth conditions in the small Stanzen areas and proceeded as in normal dishes or larger areas similarly stamped on the bottom of petri dishes. Since this method proved valuable for biochemical studies using primary cultures of mouse epidermal cells (saving cell material by a factor of 10, test substances and time), it might also be advantageous for other purposes as well where the availability of cells or test substances are limiting factors for large test series.

Animals↗
PubMed1994

Purification and characterization of the Ca2+/calmodulin-dependent protein kinase II from chicken forebrain.

CaM kinase II is known to be enriched in mammalian and avian brains. To determine the holoenzymic composition and functional characteristics of this kinase, a new approach for isolation was applied to isolate it from the chicken forebrain. Forebrains of hatched 45-d chicken were dissected, homogenized, and centrifuged. The supernatant was loaded onto a CaM-agarose affinity column and the calmodulin-binding proteins were eluted with EGTA. Selected eluates were loaded onto the antibody-agarose affinity column, which was prepared with monoclonal antibody (MAb) (6G9) to the CaM kinase II alpha subunit. Samples were subjected to SDS-polyacrylamide gel electrophoresis (SDS-PAGE) and either silver-stained or blotted onto a nitrocellulose membrane. The protein composition and the immunoreactivity of the antibody-agarose affinity eluate fractions were analyzed with a densitometric scanner. Silver staining of gels showed that the beta subunit doublet, the beta' subunit, and a putative substrate were coeluted with the alpha subunit from the antibody affinity column although only the alpha subunit bound the 6G9 antibody. Scintillation counting showed that the autophosphorylation of the kinase was significantly reduced in the eluate from the antibody affinity column. Whereas silver staining indicated an increase in the relative amount of alpha subunit had occurred during purification, phosphorylation assays indicated an increase in the relative amount of the alpha subunit after the last purification step. A possible reason for this is discussed. The presence of beta/beta' subunits in the antibody-agarose affinity eluate indicated the existence of an alpha beta/beta' heteropolymer. The phosphorylation assay was not a good indication of the amount of purification because of the loss of enzyme activity following purification. In contrast, the immunoassay indicated a 97-fold purification from the cytosolic fraction was achieved using the method. In conclusion, the data indicate the existence of the CaM kinase II alpha beta/beta' heteropolymer in the chicken forebrain.

Animals↗
PubMedDate not supplied

In vitro effect of cefodizime, imipenem/cilastatin and co-trimoxazole on dexamethasone and cyclosporin A depressed phagocytosis.

Phagocytosis is an important part of the host defense against infection. Antibiotics can influence phagocytic function. In the present study, leukocyte metabolic response to phagocytic challenge by latex was assessed in relation to in vitro addition of cotrimoxazole, imipenem/cilastatin, cefodizime, dexamethasone (DXM), and/or cyclosporin A (CsA). Using latex particles as phagocytic challenge, glucose-1-14C utilization and 14CO2 production were measured by liquid scintillation counting. The phagocytic response was impaired by in vitro addition of DXM or CsA and this setup was used as an experimental model of immunodepression. The addition of co-trimoxazole to control samples (without DXM or CsA) depressed the response to latex challenge, whereas imipenem and cefodizime had a neutral effect. In the presence of DXM, co-trimoxazole induced a further decrease. The depressive effect of DXM was partially neutralized in the presence of cefodizime. With CsA depression, co-trimoxazole also induced a further decrease, imipenem had a neutral effect, while cefodizime partially restored the CsA suppressed reaction. Co-trimoxazole depressed the phagocytic response, imipenem had a neutral effect, whereas cefodizime restored the experimentally induced immunosuppression.

Anti-Bacterial Agents↗
PubMed1986

Structural protein transport in elongating motor axons after sciatic nerve crush. Effect of a conditioning lesion.

In elongating motor axons of the rat sciatic nerve, the maximum outgrowth rate increased from 4.6 to 5.3 mm/d (5.3-6.1 X 10(-8) m/s) when a testing lesion of spinal nerves L4 and L5 was preceded 2 wk earlier by a conditioning lesion of the sciatic nerve. Axonal outgrowth was examined by measuring the transport of 35[S]methionine-labeled structural proteins (tubulin, actin, and neurofilament triplet) from "parent" axon stumps into "daughter" axon sprouts. Since these proteins are conveyed by the slow component of axonal transport at 1-5 mm/d (1.2-6.0 X 10(-8) m/s), the isotope was injected into the spinal cord 1 wk before the testing lesion. Nerves were removed 8 d after the testing lesion, sectioned into 3-mm segments, and homogenized; soluble proteins were separated by polyacrylamide gel electrophoresis. Fluorographs were used as templates to identify gel segments for removal, solubilization, and liquid scintillation counting. Distributions of mean radioactivity for tubulin, actin, and neurofilament triplet were plotted for animals receiving a conditioning vs sham-conditioning lesion. Greater amounts of tubulin and actin were transported into daughter axons in the conditioned group. Tubulin was mainly increased in axon shafts, whereas actin was mainly increased in axon tips. These findings suggest that the axonal transport of tubulin and actin governs the rate of elongation.

Actins↗