Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “RADIOACTIVITY”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

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

At least 307 records · Page 17Linked to original sources
PubMed1985

The CMP-stimulated production of diacylglycerol and CDPdiacylglycerol in neuronal nuclei labelled with radioactive arachidonate.

A neuronal nuclear fraction (N1), isolated from immature rabbit cerebral cortex, was preincubated with [3H]arachidonate, ATP, CoA, Mg2+ and 1-acyl-sn-glycero-3-phosphocholine or 1-acyl-sn-glycero-3-phosphoinositol. Using the former lysophospholipid, a sizeable incorporation of radioactivity was seen in N1 phosphatidylcholine. In subsequent incubations in the presence of CMP and EGTA, there was a generation of radioactive diacylglycerol in N1 and a corresponding decline in phosphatidylcholine radioactivity. Both these changes could be blocked by the addition of CDPcholine. In incubations using N1 phosphatidylinositol or phosphatidylethanolamine prelabelled with [3H]arachidonate, no evidence was found to support a direct generation of diacylglycerol from these phospholipids. The back reaction of cholinephosphotransferase in N1 is likely the principal source of diacylglycerols bearing arachidonate. Using either lysophospholipid in the preincubations described in the opening sentence, more than half of the incorporated radioactivity derived from [3H]arachidonate was found in N1 phosphatidylinositol. In subsequent incubations with EGTA and CMP there was a production of radioactive CDPdiacylglycerol and a decline in radioactive phosphatidylinositol. Both events could be blocked by the presence of myo-inositol. Radioactive CDPdiacylglycerol, produced in N1 in the presence of CMP and EGTA, was converted back into phosphatidylinositol by the addition of myo-inositol. The production of CDPdiacylglycerol is likely the result of the back reaction of CDPdiacylglycerol:inositol phosphatidate transferase in N1.

Animals↗
PubMed1991

Rat liver and lung mitochondria do not incorporate radioactivity from glycerol-3-phosphate or CDP-choline into glycero-3-phosphocholine.

The proposed formation of glycero-3-phosphocholine (GPC) from glycerol-3-phosphate (GP) and CDP-choline catalysed by the enzyme GPC-synthetase has been examined in liver and lung subcellular fractions. Previous observations on the incorporation of radioactive GP into the GPC-spot on paper chromatograms have been interpreted as evidence for the GPC-dependent synthesis of phosphatidylcholine. Although we could reproduce this incorporation of GP, we could not detect any incorporation of radioactive CDP-choline into the GPC-spot using the same paper chromatographic system. TLC separation of the substrate and products showed no detectable formation of GPC with either radioactive substrate. These results strongly suggest that the previously reported formation of GPC in liver and lung was due to an inaccurate identification of the true radioactive products. We demonstrate that the major radioactive product formed in liver mitochondria is glucose. A small amount of radioactive glycerol was also detected. Lung mitochondria incorporate radioactive GP into glycerol and into another unidentified compound or compounds. It is concluded that the occurrence of the GPC dependent formation of phosphatidylcholine is unlikely.

Animals↗
PubMed1983

The scintillometric evaluation of DNA repair synthesis can be distorted by changes of thymidine pool radioactivity.

The induction of DNA repair synthesis by UV radiation and methylmethane sulphonate (MMS) in mammalian cell lines of human (EUE, HeLa, FT, KB) and hamster (CHO, BHK) origin has been evaluated by means of autoradiography and the scintillometric procedure which implied the use of hydroxyurea (HU) to suppress DNA replication. While with UV radiation both methods produce concordant positive results, in the case of MMS the evidence of DNA repair synthesis obtained from the autoradiograms is occasionally accompanied by a lack of increase of DNA radioactivity in the treated cultures, as detected by scintillation counting. In such instances MMS is shown to reverse the enhancement of pool radioactivity in the cultures incubated with HU and even to reduce the radioactivity of thymidine pool below control values. By normalizing DNA radioactivities on the basis of pool variations, the discrepancy between autoradiography and scintillation counting is solved. The chromatographic analysis of thymidine pool components justifies the normalization procedure as it demonstrates that also in cultures treated with MMS or MMS + HU pool variations closely parallel the variations of thymidine triphosphate (dTTP) level. The normalization of DNA radioactivities based on the overall pool radioactivities gives an improved evaluation of the actual rate of DNA synthesis. It can be recommended for screening studies of DNA repair inducers because it allows one to correct false negative results without producing false positive data. Compared with the dTTP levels, overall pool radioactivities used as normalizing factors still produce an underestimate of DNA repair when high doses of MMS are applied to hamster cell cultures.

Animals↗
PubMed1990

Recent progress in the use of the technique of non-radioactive in situ hybridization histochemistry: new tools for molecular neurobiology.

Recent developments in DNA and oligonucleotide chemistry have made it possible to modify nucleotides and link quite complex molecules to the modified nucleotides. These advancements in DNA chemistry provide a number of possibilities for labelling oligonucleotide probes for DNA or RNA detection by non-radioactive methods. Over the years a number of non-radioactive detection systems for mRNA or chromosomal DNA have been developed. As reporter molecules, biotin, acetylaminofluorene, dinitrophenol, digoxigenin, sulfonized nucleotides, and mercury have been used and may be detected with a variety of high-affinity detectors, e.g. avidin (in the case of biotin) or antibodies specific to digoxigenin. These various 'indirect methods' of detection have used a number of chemical amplification procedures in attempts to improve their sensitivity. However, the sensitivity of these methods is often less than that of conventional radioactive methods. A sensitive non-radioactive technique would have a number of advantages over the complex and specialized radioactive in situ hybridization methods. In our laboratory we have recently found that simple enzyme-labelled probes provide excellent sensitivity (equivalent to that found with radioactive methods) and substantially improved cellular resolution. In this article, we describe the principle of the method and illustrate some applications of this novel non-radioactive in situ method.

Animals↗
PubMed1986

High resolution autoradiographic determination of the topographic distribution of radioactivity in the hippocampal formation after injection of [1-14C]glucose or 2-deoxy[14C]glucose.

Using high resolution autoradiography, the accumulation of radioactivity after intravenous injection of [1-14C]glucose was measured in the corpus callosum, hippocampus, dorsal hippocampal commissure, somatosensory cortex, inferior colliculus and pontine periaqueductal grey. Autoradiograms were prepared by thaw-mounting 4 micron frozen sections on nuclear emulsion-coated slides, and were evaluated quantitatively with a computer-assisted video system for automated counting of silver grains. In all brain regions examined, silver grain densities were greater in rats killed 30 min after injection of [1-14C]glucose compared to rats killed 10 min after injection. After intravenous injection of [1-14C]glucose or 2-deoxy[14C]glucose, the relative uptake and retention of radioactivity in different hippocampal subregions was compared. Striking differences were found in the hippocampus between 2-deoxy[14C]glucose and [1-14C]glucose autoradiograms. After injection of 2-deoxy[14C]glucose, there were large variations in the uptake and retention of radioactivity among different pyramidal cell fields. The CA 3 pyramidal cell field retained considerably more radioactivity than other pyramidal cell fields after injection of 2-deoxy[14C]glucose, while after injection of [1-14C]glucose, the retention of radioactivity was similar in all pyramidal cell fields. After [1-14C]glucose injection, the dentate gyrus contained relatively high levels of radioactivity and more 14C accumulated in the granular layer, compared to the molecular layer. In contrast, after 2-deoxy[14C]glucose injection, there was uniformly less radioactivity throughout the dentate gyrus when compared to rats injected with [1-14C]glucose and there was no preferential accumulation of 2-deoxy[14C]glucose in the granular layer compared to the molecular layer.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed2003

Metabolic distribution of radioactivity in Sprague-Dawley rats and B6C3F1 mice exposed to 1,3-[2,3-14C]-butadiene by whole body exposure.

The uptake of 1,3-[2,3-(14)C]-butadiene and its disposition, measured as radioactivity in urine, faeces, exhaled volatiles and CO(2) during and following 6 h whole body exposure to 20 ppm butadiene has been investigated in male Sprague-Dawley rats and B6C3F1 mice. Whilst there were similarities between the two species, the uptake and metabolic distribution of butadiene were somewhat different for rats and mice. The major differences observed were in the urinary excretion of radioactivity and in the exhalation of 14C-CO(2). After 42 h from the start of exposure, 51.1% of radioactivity was eliminated in rat urine compared with 39.5% for mouse urine. 34.9% of the recovered radioactivity was exhaled by rats as 14C-CO(2), compared with 48.7% by mice. Excretion of radioactivity in faeces was similar for both species (3.8% for rats and 3.4% for mice). The tissue concentrations of 14C-butadiene equivalents measured in liver, testes, lung and blood of exposed mice were 0.493, 0460, 0.457, and 1.626 nmol/g tissue, respectively. The values for the corresponding rat tissues were 0.869, 0.329, 0.457, and 1.626 nmol butadiene equivalents/g tissue, respectively. For rats, 6.2% of recovered radioactivity (0.288 nmol butadiene equivalents/g tissue) was retained in carcasses whereas for mice the amount was 3.6% (0.334 nmol butadiene equivalents/g tissue). There were also some significant differences between the metabolic conversion of 1,3-[2,3-(14)C]-butadiene and excretion by mice following the 20 ppm whole body exposure compared to previously reported data for nose-only exposure to 200 ppm butadiene [Richardson et al., Toxicol. Sci. 49 (1999) 186]. The main difference between the high- and low-exposure studies was in the exhalation of 14C-CO(2). At the 200 ppm exposure, 40% of the radioactivity was exhaled as 14C-CO(2) by rats whereas 6% was measured by this route for mice. The proportional conversion of butadiene to CO(2) by mice was significantly greater at the low exposure concentration compared with that reported for the higher concentration. This shift was not observed for rats. The difference between species could be caused by a saturation of metabolism in mice between 20 and 200 ppm for the pathways leading to CO(2). Restraint or error in collection of CO(2) in the 200 ppm study could also be factors.

Animals↗
PubMed1998

Electrodeposition of radioactive rhenium onto stents to prevent restenosis.

Radioactive stents are currently being evaluated for preventing restenosis. A major difficulty to overcome is the need to load any pre-manufactured stents with defined amounts of radioactivity at the time of use. Using stents that are preloaded by the manufacturer is not ideal because the stent length usually differs from the length needed for a specific lesion and the amounts of radioactivity varies widely due to ongoing decay of the source. Thus, we have developed a novel method that allows any currently used stainless steel or tantalum stent to be coated with radioactive rhenium. The method involves placing the stent in a series of rinsing and electroplating solutions, one containing radioactive rhenium (186Re, 188Re, or both). The overall processing time is 15 min and the procedure may be conveniently applied just prior to the stent insertion. The plated stent contains radioactive rhenium in a 1.2 microm-thick cobalt layer, with an outer 2 microm layer of gold. The gold layer gives the radioactive stent excellent radiochemical stability, good bending and biocompatibility properties, and improves stent visibility during fluoroscopy.

Angioplasty, Balloon, Coronary↗
PubMed1999

Hepatic tumor radioembolization in a rat model using radioactive rhenium (186Re/188Re) glass microspheres.

PURPOSE: The aim of this study was to fully characterize newly developed radioactive rhenium glass microspheres in vivo by determining their biodistribution, stability, antitumor effect, and toxicity after hepatic arterial injection in a syngeneic rat hepatoma model. The dose response of the tumors to increasing amounts of radioactive 186Re and 188Re microspheres was also determined. METHODS AND MATERIALS: Rhenium glass microspheres were made radioactive by neutron activation and then injected into the hepatic artery of Sprague-Dawley rats containing 1-week-old Novikoff hepatomas. The biodistribution of the radioactivity and tumor growth were determined 1 h and 14 days after injection. RESULTS: Examination of the biodistribution indicated a time-dependent, up to 7-fold increase in Novikoff hepatoma uptake as compared to healthy liver tissue uptake. After 14 days, the average T:L ratio was 1.97. Tumor growth in the rats receiving radioactive microspheres was significantly lower than in the group receiving nonradioactive microspheres (142% vs. 4824%, p = 0.048). Immediately after injection, 0.065% of the injected radioactivity was measured in the thyroid; it decreased to background levels within 24 h. CONCLUSION: Radioactive rhenium microspheres are effective in diminishing tumor growth without altering hepatic enzyme levels. The microspheres are safe with respect to their radiation dose to healthy tissue and radiation release in vivo and can be directly imaged in the body with a gamma camera. Furthermore, rhenium microspheres have an advantage over pure beta-emitting microspheres in terms of preparation and neutron-activation time. In sum, this novel radiopharmaceutical may provide an innovative and cost-effective approach for the treatment of nonresectable liver cancer.

Animals↗
PubMed1999

Elimination of nonspecific radioactivity from [76Br]bromide in PET study with [76Br]bromodeoxyuridine.

[76Br]Bromodeoxyuridine ([76Br]BrdU) might allow a determination of proliferation in vivo using positron emission tomography (PET), but only with consideration of organ nonspecific radioactivity constituted by [76Br]bromide. A first study assessed the potential of diuretics to eliminate [76Br]bromide. [76Br]Bromide was injected in the vein of rats and different diuretic combinations were given. Urine was collected and radioactivity measured. Torasemide plus sodium chloride gave better 76Br elimination than the other diuretics. In a second experiment, rats were given [76Br]BrdU. After the radioactivity injection, the rats of the treatment group were given torasemide plus NaCl. At 44 h after the radioactivity injection, the radioactivity concentration and the fraction incorporated into DNA were measured in different organs. Using diuretics, the elimination of [76Br]bromide was increased. The radioactivity decreased 30-50% in most of the organs but the highest radioactivity uptake was found in the organs with more active DNA synthesis. This method may facilitate the use of [76Br]BrdU as a tracer for DNA synthesis using PET.

Animals↗
PubMedDate not supplied

Design, synthesis, and evaluation of [188Re]organorhenium-labeled antibody fragments with renal enzyme-cleavable linkage for low renal radioactivity levels.

Renal localization of radiolabeled antibody fragments constitutes a problem in targeted imaging and radiotherapy. We have reported that Fab fragments labeled with 3'-[131I]iodohippuryl Nepsilon-maleoyl-lysine (HML) showed markedly low renal radioactivity levels even shortly after injection, due to a rapid and selective release of m-[131I]iodohippuric acid by the action of brush border enzymes. To estimate the applicability of the molecular design to metallic radionuclides, [188Re]tricarbonyl(cyclopentadienylcarbonate)rhenium ([188Re]CpTR-COOH) was conjugated with Nepsilon-tert-butoxycarbonyl-glycyl-lysine or Nepsilon-maleoyl-glycyl-lysine to prepare [188Re]CpTR-GK-Boc or [188Re]CpTR-GK. The cleavage of the glycyl-lysine linkage of the two compounds generates a glycine conjugate of [188Re]CpTR-COOH ([188Re]CpTR-Gly), which possesses in vivo behaviors similar to those of m-iodohippuric acid. The hydrolysis rate of the peptide bond in [188Re]CpTR-GK-Boc was compared with that in 3'-[125I]iodohippuryl Nepsilon-Boc-lysine ([125I]HL-Boc) using brush border membrane vesicles (BBMVs) prepared from rat kidneys. [188Re]CpTR-GK was conjugated to thiolated Fab fragments to prepare [188Re]CpTR-GK-Fab. The biodistribution of radioactivity after injection of [188Re]CpTR-GK-Fab was compared with that of [125I]HML-Fab and [188Re]CpTR-Fab prepared by conjugating N-hydroxysuccinimidyl ester of [188Re]CpTR-COOH with antibody fragments. While [188Re]CpTR-GK-Boc liberated [188Re]CpTR-Gly in BBMVs, [125I]HL-Boc liberated m-[125I]iodohippuric acid at a much faster rate. In addition, although [125I]HL-Boc was hydrolyzed by both metalloenzymes and nonmetalloenzymes, metalloenzymes were responsible for the cleavage of the peptide linkage in [188Re]CpTR-GK-Boc. In biodistribution studies, [188Re]CpTR-GK-Fab exhibited significantly lower renal radioactivity levels than did [188Re]CpTR-Fab. However, the renal radioactivity levels of [188Re]CpTR-GK-Fab were slightly higher than those of [125I]HML-Fab. The analysis of urine samples collected for 6 h postinjection of [188Re]CpTR-GK-Fab showed that [188Re]CpTR-Gly was the major radiometabolite. In tumor-bearing mice, [188Re]CpTR-GK-Fab significantly reduced renal radioactivity levels without impairing the radioactivity levels in tumor. These findings indicate that the molecular design of HML can be applied to metallic radionuclides by using a radiometal chelate of high inertness and by designing a radiometabolite of high urinary excretion when released from antibody fragments following cleavage of a glycyl-lysine linkage. This study also indicates that a change in chemical structure of a radiolabel attached to a glycyl-lysine linkage significantly affected enzymes involved in the hydrolysis reaction. Since there are many kinds of enzymes that cleave a variety of peptide linkages on the renal brush border membrane, selection of a peptide linkage optimal to a radiometal chelate of interest may provide radiolabeled antibody fragments that exhibit renal radioactivity levels similar to those of [131I]HML-labeled ones. The in vitro system using BBMVs might be useful for selecting an appropriate peptide linkage.

Animals↗
PubMedDate not supplied

Intracellular metabolic fate of radioactivity after injection of technetium-99m-labeled hydrazino nicotinamide derivatized proteins.

Hydrazino nicotinate (HYNIC) has been shown to produce technetium-99m (99mTc)-labeled proteins and peptides of high stability with high specific activities. However, persistent localization of radioactivity was observed in nontarget tissues such as the liver and kidney after administration of [99mTc]HYNIC-labeled proteins and peptides, which compromises the diagnostic accuracy of the radiopharmaceuticals. Since lysosomes are the principal sites of intracellular catabolism of proteins and peptides, 99mTc-HYNIC-labeled galactosyl-neoglycoalbumin (NGA) was prepared using tricine as a co-ligand to investigate the fate of the radiolabel after lysosomal proteolysis in hepatocytes. When injected into mice, over 90% of the injected radioactivity was accumulated in the liver after 10 min injection. At 24 h postinjection, ca. 40% of the injected radioactivity still remained in liver lysosomes. Size-exclusion HPLC analyses of liver homogenates at 24 h postinjection showed a broad radioactivity peak ranging from molecular masses of 0.5-50 kDa. RP-HPLC analyses of liver homogenates suggested the presence of multiple radiolabeled species. However, most of the radioactivity migrated to lower molecular weight fractions on size-exclusion HPLC after treatment of the liver homogenates with sodium triphenylphosphine-3-monosulfonate (TPPMS). The TPPMS-treated liver homogenates showed a major peak at a retention time similar to that of [[99mTc](HYNIC-lysine)(tricine)(TPPMS)] on RP-HPLC. Similar results were obtained with urine and fecal samples. These findings suggested that the chemical bonding between 99mTc and HYNIC remains stable in the lysosomes and following excretion from the body. The persistent localization of radioactivity in the liver could be attributed to the slow elimination rate of the final radiometabolite, [[99mTc](HYNIC-lysine)(tricine)2], from lysosomes, and subsequent dissociation of one of the tricine co-ligands in the low pH environment of the lysosomes in the absence of excess co-ligands, followed by binding proteins present in the organelles. The findings in this study also suggested that the development of appropriate co-ligands capable of preserving stable bonding with the Tc center is essential to reduce the residence time of radioactivity in nontarget tissues after administration of [99mTc]HYNIC-labeled proteins and peptides.

Albumins↗
PubMed2005

Effect of sodium [36Cl]chlorate dose on total radioactive residues and residues of parent chlorate in beef cattle.

The objectives of this study were to determine total radioactive residues and chlorate residues in edible tissues of cattle administered at three levels of sodium [36Cl]chlorate over a 24-h period and slaughtered after a 24-h withdrawal period. Three sets of cattle, each consisting of a heifer and a steer, were intraruminally dosed with a total of 21, 42, or 63 mg of sodium [36Cl]chlorate/kg of body weight. To simulate a 24-h exposure, equal aliquots of the respective doses were administered to each animal at 0, 8, 16, and 24 h. Urine and feces were collected in 12-h increments for the duration of the 48-h study. At 24 h after the last chlorate exposure, cattle were slaughtered and edible tissues were collected. Urine and tissue samples were analyzed for total radioactive residues and for metabolites. Elimination of radioactivity in urine and feces equaled 20, 33, and 48% of the total dose for the low, medium, and high doses, respectively. Chlorate and chloride were the only radioactive chlorine species present in urine; the fraction of chlorate present as a percentage of the total urine radioactivity decreased with time regardless of the dose. Chloride was the major radioactive residue present in edible tissues, comprising over 98% of the tissue radioactivity for all animals. Chlorate concentrations in edible tissues ranged from nondetectable to an average of 0.41 ppm in skeletal muscle of the high-dosed animals. No evidence for the presence of chlorite was observed in any tissue. Results of this study suggest that further development of chlorate as a preharvest food safety tool merits consideration.

Animals↗
PubMed1994

Maleimidoethyl 3-(tri-n-butylstannyl)hippurate: a useful radioiodination reagent for protein radiopharmaceuticals to enhance target selective radioactivity localization.

In pursuit of radiolabeled monoclonal antibodies (mAbs) with rapid urinary excretion of radioactivity from nontarget tissues, radioiodinated mAbs releasing a m-iodohippuric acid from the mAbs in nontarget tissues were designed. A novel reagent, maleimidoethyl 3-(tri-n-butylstannyl)hippurate (MIH), was synthesized by reacting N-(hydroxyethyl)maleimide with N-Boc-glycine before coupling with N-succinimidyl 3-(tri-n-butylstannyl)benzoate (ATE). MIH possessed a maleimide group for mAb conjugation and a butylstannyl moiety for high-yield and site-specific radioiodination, and the two functional groups were linked via an ester bond to release m-iodohippuric acid. To investigate the fate of radiolabels after lysosomal proteolysis, hepatic parenchymal cells were used as a model nontarget tissue and 131I-labeled MIH was conjugated with galactosyl-neoglycoalbumin (NGA). Further conjugation of [131I]MIH with a mAb against osteogenic sarcoma (OST7) after reduction of its disulfide bonds was followed up. In murine biodistribution studies, [131I]MIH-NGA exhibited rapid accumulation in the liver followed by radioactivity elimination from the liver at a rate that was identical to and faster than those of 131I-labeled NGA via direct iodination ([131I]NGA) and [131I]ATE-labeled NGA, respectively. While [131I]NGA indicated high radioactivity levels in the murine neck, stomach, and blood, such increases in the radioactivity count were not detectable by the administration of either [131I]MIH-NGA or [131I]ATE-NGA. At 6 h postinjection of [131I]MIH-NGA, 80% of the injected radioactivity was recovered in the urine. Analyses of urine samples indicated that m-iodohippuric acid was the sole radiolabeled metabolite. In biodistribution studies using [131I]-MIH-OST7 and [131I]ATE-OST7, while both 131I-labeled OST7s registered almost identical radioactivity levels in the blood up to 6 h postinjection, the former demonstrated a lower radioactivity level than [131I]ATE-OST7 in nontarget tissues throughout the experiment. Such chemical and biological characteristics of MIH would enable high target/nontarget ratios in diagnostic and therapeutic nuclear medicine using mAbs and other polypeptides.

Albumins↗
PubMed1971

The binding of radioactive label from labelled phenacetin and related compounds to rat tissues in vivo and to nucleic acids and bovine plasma albumin in vitro.

1. acetyl-(3)H- and ethyl-(14)C-labelled derivatives of phenacetin and related compounds are described. 2. Radioactive label from the ethyl-(14)C-labelled derivatives of 4-nitrophenetole, 4-phenetidine and phenacetin binds in vitro to various extents to bovine plasma albumin, salmon sperm DNA and yeast RNA; the extent of binding is increased in the presence of a rat liver microsomal hydroxylating system and further increased when the microsomal enymes are induced by prior treatment of rats with 3-methylcholanthrene. 3. The ratios of the bound radioactive labels in vitro from [ethyl-(14)C]phenacetin, N-acetoxy[ethyl-(14)C]phenacetin, [acetyl-(3)H]phenacetin and [diacetyl-(3)H]N-acetoxyphenacetin per g-atom of DNA P, RNA P and per mol of protein in the absence of the microsomal system are approximately 1:60:11:863, 1:68:41:1835 and 1:88:713:2399 respectively. 4. Radioactive label from labelled phenacetin binds in vitro to all tissues examined, including the spleen, intestines, kidney and bladder; about 80% of the radioactivity bound to the liver is concentrated in the RNA and proteins. 5. Comparison of the relative extents of binding of radioactive label derived from equimolar amounts of labelled phenacetin, ethanol or acetate shows that the incorporation of labelled C(2) units into tissues and biological macromolecules in vivo and in vitro may account for only a part of the total bound radioactive label derived from phenacetin and not at all from the incorporation of radioactive acetate into nucleic acids. 6. Some implications of these findings are discussed.

Animals↗
PubMed1974

The specific radioactivity of the tissue free amino acid pool as a basis for measuring the rate of protein synthesis in the rat in vivo.

1. Rats were infused in vivo with [U-(14)C]glycine for periods of 2-6h, during which time the specific radioactivity of the free glycine in plasma and tissue approached a constant value. 2. Free serine also became labelled. The ratio of specific radioactivity of serine to that of glycine in the protein of liver, kidney, brain, jejunum, heart, diaphragm and gastrocnemius muscle was closer to the ratio in the free amino acid pool of the tissue than that of the plasma. 3. The kinetics of incorporation of [(14)C]glycine and [(14)C]serine into the protein of gastrocnemius muscle further suggested that the plasma free amino acids were not the immediate precursors of protein. 4. Infusion of rats with [U-(14)C]serine resulted in labelling of free glycine. The ratio of specific radioactivity of glycine to serine in the protein of liver, kidney, brain, jejunum and heart again suggested incorporation from a pool similar to the free amino acid pool of the tissue. 5. Rates of tissue protein synthesis calculated from the incorporation into protein of both radioactive glycine and serine, either infused or derived, were very similar when the precursor specific radioactivity was taken to be that in the total free amino acids of the tissue. Except for gastrocnemius muscle and diaphragm during the infusion of radioactive serine, the rates of tissue protein synthesis calculated from the specific radioactivity of the free glycine and serine in plasma differed markedly.

Amino Acids↗
PubMed1980

The incorporation of radioactive fatty acids into the phospholipids of nerve-cell-body membranes in vivo.

1. Nerve cell bodies were isolated in bulk from cerebral cortices of 15 day-old rabbits after intrathecal injections of [(3)H]plamitate, [(3)H]oleate or [(3)H]arachidonate and [(14)C]glycerol. 2. Nuclear, microsomal and two mitochondrial fractions were isolated from homogenates of the radioactively labelled nerve cell bodies by using differential and discontinuous-gradient centrifugation. 3. After 7.5min in vivo, a high percentage (>80%) of the total (3)H-labelled fatty acid radioactivity was found in the membrane fractions of the nerve cell bodies, whereas after 60min in vivo 50% of the total [(14)C]glycerol radioactivity was found in the high-speed supernatant. 4. The specific radioactivities of phosphatidylcholine, phosphatidylethanolamine and phosphatidylinositol, and the radioactivity in neutral lipid and non-esterified fatty acid fractions were determined in the four subfractions, as were the distributions of several marker enzymes and nucleates. 5. With respect of (3)H-labelled fatty acid, the phospholipids of the nuclear fraction had the highest specific radioactivities of the four subfractions. However, for [(14)C]glycerol labelling, generally the (14)C specific radioactivities for individual phospholipids were comparable in the four subfractions. This latter observation suggests transport of phospholipids synthesized de novo between membranes of the nerve cell body. 6. Double-labelling experiments demonstrated that individual phospholipids and the combined neutral lipids of the nuclear fraction had higher labelling ratios of (3)H-labelled fatty acid/[(14)C]glycerol than did the corresponding lipids of the microsomal or mitochondrial fractions. 7. On the basis of the labelling results and the marker studies, it is proposed that it is indeed the nuclei of the nuclear fraction that have these lipids highly labelled with (3)H-labelled fatty acid, and the existence of nuclear acyl transferases that are responsible for this fatty acid incorporation is suggested.

Animals↗
PubMed1985

Analytical errors in measuring radioactivity in cell proteins and their effect on estimates of protein turnover in L cells.

Previous studies from this laboratory on protein turnover in 3H-labelled L-cell cultures have shown recovery of total 3H at the end of a 3-day experiment to be always significantly in excess of the 3H recovered at the beginning of the experiment. In this study we have critically reviewed a number of possible sources for this error in measuring radioactivity in cell proteins. 3H-labelled proteins, when dissolved in 0.3 M-NaOH and counted for radioactivity in a liquid-scintillation spectrometer, showed losses of 30-40% of the radioactivity; neither external or internal standardization compensated for this loss. Hydrolysis of these proteins with either Pronase or concentrated HCl significantly increased the measured radioactivity. In addition, approx. 5-10% of the cell protein is left on the plastic culture dish when cells are recovered in phosphate-buffered saline. To aggravate this latter loss further, this surface-adherent protein, after pulse labelling, contains proteins of high radioactivity that turn over rapidly and make a major contribution to the accumulating radioactivity in the medium. These combined errors can account for up to 60% of the total radioactivity in the cell culture. Similar analytical errors have been found in studies of other cell cultures. The effect of these analytical errors on estimates of protein turnover in cell cultures is discussed.

Animals↗
PubMed2001

Pharmacokinetics of NS-49, a phenethylamine class alpha 1A-adrenoceptor agonist. 4th communication: tissue distribution, placental transfer and milk secretion of radioactivity in rats after a single oral administration of 14C-NS-49, and effects of repeated administration on its pharmacokinetics.

The tissue distribution, placental transfer and milk secretion of 14C-NS-49 ((R)-(-)-3'-(2-amino-1-hydroxyethyl)-4'-fluoro-methanesulfonanilide hydrochloride, CAS 137431-04-0), a phenethylamine class alpha 1A-adrenoceptor agonist, have been studied after a single oral administration (1 mg/kg) of a suspension formulation to rats. Radioactivity concentrations in tissues were generally highest 1 or 4 h, and for most tissues, exceeded those in the corresponding plasma. Concentrations were generally similar in male and female rats and persisted for at least 24 h. Radioactivity concentrations in most tissues declined in parallel with those in plasma. Placental transfer of radioactivity was low accounting for < 0.1% of the maternal dose. In milk, concentrations were of a similar order to those in the plasma but reached a peak later: the data implied that 14C-NS-49 readily diffused from the plasma into the milk. The absorption, distribution and excretion of 14C-NS-49 have been studied after the repeated administration (1 mg/kg) of a suspension formulation to rats for up to 21 days. At 21 days, radioactivity concentrations in plasma reached a peak 1 h and declined with a terminal half-life of 67 h. Steady state concentrations were reached during 14 days. Peak concentrations in tissues occurred 1 h and, in most tissues exceeded the plasma value. Radioactivity concentrations in tissues appeared to reach steady state during the 21-day dosing period. Tissue and blood cell concentrations declined more slowly than those in the plasma. Radioactivity excretion was relatively constant during the repeated administration and similar in urine (mean 45.8% total dose) and feces (mean 48.2% total dose). At 7 days after the last of 21 daily oral doses, only 0.2% of the total dose remained in the body, indicating that there is no marked accumulation of radioactivity in the tissues. The results obtained in these studies indicated that rats receiving NS-49 at 24 h intervals during chronic and reproductive toxicity studies would be continually exposed to the parent compound and/or its metabolites.

Adrenergic alpha-1 Receptor Agonists↗