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 361 records · Page 20Linked to original sources
PubMed1997

Production and evaluation of non-radioactive probes for the detection of the two 'Candidatus Liberobacter' species associated with citrus huanglongbing (greening).

The production and evaluation of non-radioactive probes for the detection of 'Candidatus Liberobacter asiaticum' and 'Candidatus Liberobacter africanum', the two bacterial species associated with citrus huanglongbing (greening) disease is described. Two DNA fagments, In 2.6 and AS 1.7, obtained previously from the beta operons of 'Candidatus Liberobacter asiaticum' and 'Candidatus Liberobacter africanum', respectively, were the starting materials for production of the two non-radioactive probes. These digoxigenin (DIG)-labelled probes were generated by PCR incorporation of DIG-11-dUTP, yielding In 1.7-DIG and AS 1.7-DIG. Probe In 1.7-DIG was hybridized with DNAs extracted from 24 field-collected samples in Bali (Indonesia). The membrane on which the DNAs were blotted was first hybridized with radioactive probe 32P-In 2.6. After the hybridization results were recorded, the radioactive probe was removed, and the membrane hybridized with DIG-labelled probe In 1.7-DIG. Identical results were obtained for 23 samples. One sample was positive with the DIG-labelled probe and negative with the 32P-labelled probe. However, cross-hybridization of In 1.7-DIG with DNA from L. africanum was higher than that obtained with the radioactive probe. This cross-hybridization could be eliminated by raising the temperature of the stringent washing step. No field samples from Africa being available, probe AS 1.7-DIG was dot-blot hybridized against DNAs extracted from leaves of greenhouse-kept citrus plants from different geographical origins and infected with one or other Liberobacter species. The data showed that AS 1.7-DIG hybridized with L. africanum with a sensitivity equivalent to that of the radioactive probe.

Citrus↗
PubMed1976

Radioactivity in urine and feces of mink (Mustela vison) treated with [14C] aflatoxin B1.

Excretion of radioactivity by mink (Mustela vison) during 7 days after intraperitoneal injection of two different amounts of aflatoxin B1 was studied. Male mink that received a single dose of 25 mug aflatoxin B1/kg body weight excreted an average of 89.5% of administered radioactivity (56.8% via feces, 32.7% via urine); whereas female mink excreted an average of 85% (63.6% via feces, 21.4% via urine) of administered radioactivity during the 7-day period. Male and female mink given 150 mug aflatoxin B1/kg body weight excreted an average of 76.9-80.1% of administered radioactivity during the 7 days that followed treatment with toxin. These mink excreted somewhat more of the administered radioactivity in their urine than did the mink that received the lower dose of aflatoxin (37.2 vs. 32.7% for males and 32.7 vs. 21.4% for females). Regardless of sex and dosage of toxin, most of the radioactivity ultimately excreted either through feces or urine appeared in the first 24 h after toxin was administered to mink.

Aflatoxins↗
PubMed1990

Topography and ontogeny of the neurons expressing vasopressin, oxytocin, and somatostatin genes in the rat brain: an analysis using radioactive and biotinylated oligonucleotides.

1. The use of radioactive and biotinylated oligonucleotide probes has been optimized to detect and analyze by in situ hybridization, neurons expressing neuropeptide genes (vasopressin, oxytocin, somatostatin). 2. In situ hybridization was performed on cryostat-cut sections obtained from tissues perfused with 1% formaldehyde. Radioactive probes were labeled by tailing with 35S-dATP and revealed with autoradiography. Biotinylated probes were obtained either by the incorporation of 11-biotin dUTP or by the addition of biotinylated nucleotides to the oligonucleotide during its synthesis. Biotin was revealed with streptavidin alkaline phosphatase and the appropriate substrate. 3. In the adult rat brain, radioactive and biotinylated probes revealed peptidergic neurons. The biotinylated probes provided an optimal cellular and subcellular resolution with a sensitivity similar to that observed with radioactive probes. Staining was selectively restricted to the cytoplasm and to the proximal part of processes. 4. Biotinylated vasopressin probes with 10 biotins added demonstrated magnocellular neurons and parvocellular neurons in the suprachiasmatic nucleus and the bed nucleus stria terminalis. 5. Vasopressin gene expression was studied during ontogeny in the rat fetus and neonate. Vasopressin mRNA was first detectable at gestational day 16 in the supraoptic nucleus in neurons of neuroblastic appearance. An aspect similar to the one present in adult was found at gestational day 19 in magnocellular neurons and at day 3 postnatal in parvocellular neurons. 6. The results confirm that radioactive oligonucleotide probes are efficient tools to investigate neuropeptide gene expression by in situ hybridization and demonstrate that biotinylated oligonucleotides are very efficient and provide a much higher resolution than radioactive probes with a reasonable sensitivity.

Animals↗
PubMed1989

Radioactive labeling of proteins in cultured postimplantation mouse embryos. I. Influence of the embryo preparation method.

Conditions for optimum incorporation of radioactive amino acids into proteins of cultured postimplantation mouse embryos were investigated under the aspect of using these proteins for two-dimensional electrophoretic separations followed by fluorography. The aim was to obtain highly radioactive proteins under conditions as physiological as possible. Embryos at Days 10, 11, and 12 of gestation were prepared in different ways and incubated for 4 h in Tyrode's solution containing [3H]amino acids (mixture) at a concentration of 27 microCi/ml medium. The preparations were: a) yolk sac opened, placenta and blood circulation intact; b) yolk sac and amnion opened, placenta and blood circulation intact (Day 10 embryos only); c) placenta, yolk sac, and amnion removed (embryo "naked"); d) naked embryos cut randomly into pieces (Day 10 embryos only). After incubation whole embryos or certain parts (tail, liver, rest body) were investigated by determining the radioactivity taken up by the protein. The results are given in dpm per mg protein per embryo. Radioactivity of proteins was about 3 times higher in naked embryos than in embryos left in their yolk sacs. This was true for all three stages investigated. However, the degree of radioactivity in the various parts of naked embryos differed by a factor of 15, whereas radioactivity was evenly distributed in embryos incubated in their yolk sacs. Therefore, embryos prepared according to the first method (see above) fulfilled the conditions required at the best.

Amino Acids↗
PubMed2005

Biodistribution and excretion of radioactivity after the administration of 166Ho-chitosan complex (DW-166HC) into the prostate of rat.

PURPOSE: The objective of this study was to determine the fate of the 166Ho-chitosan complex (DW-166HC) in rats by examining its absorption, distribution and excretion after administration into the prostate. METHODS: About 100 microCi of DW-166HC [containing 0.1875 mg of Ho(NO3)3.5H2O and 0.25 mg of chitosan] was administered intraprostatically. The level of radioactivity in blood, urinary and faecal excretion, and radioactivity distribution were examined. To determine the effect of chitosan in DW-166HC, 166Ho nitrate alone [0.1875 mg of Ho(NO3)3.5H2O] was administered into the prostate of male rats, and radioactivity distribution was examined using whole-body autoradiography. RESULTS: After administration of DW-166HC into the prostate, cumulative urinary and faecal excretion over the period 0-72 h was 0.35% and 0.11%, respectively. The radioactivity at the administration site was extremely high at all time points up to 144 h (>98% of injected dose). The small amount of radioactivity which did transfer from the administration site distributed mainly to the liver, spleen, kidney cortex and bone. Compared with the DW-166HC group, the group that received 166Ho nitrate alone displayed three- to fourfold higher levels of radioactivity in the main tissues, including liver, spleen, kidney cortex and bone, at 24 h after administration (P < 0.05). CONCLUSION: The results of this study show clearly that most of the administered DW-166HC remained at the administration site. It is concluded that the chitosan complex may be used to retain 166Ho within a limited area in cancer of the prostate.

Animals↗
PubMed1977

Metal isotopes used as radioactive indicators of ocular melanoma.

We studied radioactive metal compounds to determine their localization in malignant Greene melanoma in the eye of the Syrian golden hamsters. Scintigraphy of an ocular melanoma was achieved with several radioactive metals: radioactive indium(111In)-bleomycin, radioactive gallium (67Ga)-citrate, and radioactive lead (203Pb)-tris. The 111In-bleomycin had the highest tumor uptake (5.45% dose/g), but not the highest tumor-to-background ratios. The 67Ga-citrate had a maximum tumor uptake of 4.87% dose/g at 48 hours. The 111In-chloride had a melanoma uptake of 2.26% dose/g, while with 203Pbtris the uptake was 1.61% dose/g. These uptake ratios compare favorably with that of radioactive phosphorus (32P)-2.21% dose/g. Noninvasive localization of malignant melanoma in the eye was accomplished with metal isotopes. Detailed analysis of in vitro uptake date by tumor and background tissues revealed the optimum time for scanning and precluded unnecessary trials.

Animals↗
PubMed1983

Tissue locations for the turnover of radioactively labeled rat orosomucoid in vivo.

Tissues involved in the turnover of rat serum orosomucoid were identified by methods designed to cause lysosomal trapping of radiolabel at the sites of glycoprotein degradation. 125I-, [3H]Raffinose-, and [1-14C]glucosamine-labeled orosomucoid exhibited serum half-lives of 20, 20, and 27 h when injected intravenously into rats. As expected, the asialo derivative of [3H]raffinose-labeled rat orosomucoid was lost very rapidly from the circulation and recovered quantitatively in the liver within 30 min. At 50 h after injection of [3H]raffinose-asialo-orosomucoid the liver retained 38% of the radioactivity while the remainder was found in the gastrointestinal tract and urine. Chromatography of the urine on Bio-Gel P-4 revealed a single radioactive product that eluted similar to raffinose-lysine. The same material was found in the liver. This ability of the [3H]raffinose label to resist metabolic disposal was used to evaluate tissue catabolism of native rat orosomucoid. Comparison of the tissue radioactivity in experiments using 125I- and [3H]raffinose-labeled derivatives of the nondesialylated glycoprotein showed kidney, liver, and muscle to be most active in 3H accumulation. However, the [3H]raffinose metabolites excreted in the urine was markedly different from those produced from asialo-orosomucoid and in contrast there was minimal loss of label to the gastrointestinal tract from the native substrate. Leupeptin, an inhibitor of lysosomal thiol cathespins, was administered continuously to rats by a subcutaneous osmotic pump. At 24 h after injection of 125I-orosomucoid, leupeptin-treated rats showed a net 16% increase in tissue radioactivity above sham-operated animals and a corresponding decrease occurred in the radioactivity associated with the gastrointestinal tract and urine. Tissues that exhibited increases in radioactivity were kidney, muscle, liver, and hide. The different behavior of labeled native and asialo-orosomucoids suggests that the hepatic galactose receptor system plays, at most, a limited role in maintaining homeostasis of the native glycoprotein.

Animals↗
PubMed1986

Release of endogenous and radioactive purines from the rabbit retina.

The adenine nucleotide pool of rabbit retina was labeled by an intravitreal injection in vivo of [3H]adenosine. Practically all the radioactivity was retained in the form of adenine nucleotides. The relative proportion of [3H]adenine nucleotides was the same as that of endogenous nucleotides. Potassium depolarization (43.6 mM) in vitro caused a rapid increase in the rate of release of radioactive purines. The radioactive material was composed of hypoxanthine, xanthine, inosine and trace amounts of adenine, adenosine and adenine nucleotides. The release of radioactive purines was delayed and reduced by the addition of the nucleoside inhibitor dipyridamole suggesting that the purines may be released in the form of nucleosides. Similarly, the addition of the ecto 5'-nucleotidase inhibitor alpha, beta-methylene ADP (AOPCP) did not alter the release of radioactivity or the composition of the released purines. Endogenous hypoxanthine, xanthine and inosine could be detected in the effluents, but there was only a very modest increase following potassium depolarization. There was a slight, but significant, decrease in the release of endogenous adenosine and increase in AMP after AOPCP. It is concluded that there is an intensive uptake and phosphorylation of adenosine in the rabbit retina. Depolarization induces release of radioactive purine nucleosides and bases. Most of these compounds appear to be released as such, but in addition there may be a small (maximally a few per cent of the total) fraction of the purines that are released as nucleotides.

Adenine↗
PubMed1981

A method for the estimation of amino acid radioactivity in biological samples.

A method for quantitative estimation of total radioactivity present in the free amino acid fraction of tissue samples has been described. Samples deproteinized with cold acetone were extracted, in acidic medium, with ethyl ether (peroxide free); after centrifugation, the aqueous phase was used for amino acid derivatization at 40 degrees C for 15 h with 1-fluoro-2,4-dinitrobenzene in bicarbonate-buffered medium. Aliquots of the derivatized samples were acidified and extracted twice again with ethyl ether. The combined organic phases were placed in glass scintillation vials, dried, and used for the determination of its radioactivity, corresponding to the radioactivity present in the free amino acid fraction of the sample. Deproteinized samples of rat blood plasma, as well as hen egg white and yolk were tested after addition of known quantities of 14C-labelled amino acids or glucose, for validation of the method. No glucose radioactivity was found in any of the extracted samples. All radioactivity added to the samples in the form of 14C-labelled alanine, glutamic acid, leucine and phenylalanine was quantitatively recovered in the derivatized fraction; only a fraction of arginine radioactivity was recovered.

Amino Acids↗
PubMed1994

Quantitative detection of hepatitis B virus DNA in serum using chemiluminescence: comparison with radioactive solution hybridization assay.

A quantitative, non-radioactive hybrid capture HBV DNA assay (Digene Diagnostics), which uses an efficient solution hybridization procedure coupled to a sensitive chemiluminescent signal amplification system, was compared with the quantitative, radioactive solution hybridization assay (Genostics, Abbott Laboratories), in hepatitis B virus carriers, particularly in those undergoing antiviral therapy. The qualitative reproducibility of the chemiluminescent method, tested on 30 sera, was acceptable, with a reproducibility rate of 93.3%. A comparison of this hybrid capture HBV DNA assay with the radioactive test on 113 sera obtained from 48 patients (39 HBsAg-positive patients) gave a sensitivity of 87.2%, a specificity of 100% and an agreement between the two tests of 89.4% (101 sera including 82 HBV DNA positive and 19 negative samples). Changes in HBV DNA levels measured by the two assays showed a good correlation with each other during interferon therapy. However, the hybrid capture values were higher than the radioactive assay values, with the ratio of the two values being variable in the same patient during the course of treatment. The Genostics assay therefore seems to be a more accurate procedure for evaluating changes in viral replication, particularly at high HBV DNA levels. However, the hybrid capture method is faster and has the advantage of being a non-radioactive procedure. This chemiluminescent assay is easy to perform as a routine diagnostic procedure and may be a useful alternative to the radioactive solution hybridization method.

Carrier State↗
PubMed2006

Analysis of 18F-labelled synthesis products on TLC plates: comparison of radioactivity scanning, film autoradiography, and a phosphoimaging technique.

We compared radioactivity scanning, film autoradiography, and digital photostimulated luminescence (PSL) autoradiography (phosphoimaging technique) in detection of radioactivity on thin-layer chromatography (TLC) plates. TLC combined with radioactivity detection is rapid, simple, and relatively flexible. Here, (18)F-labelled synthesis products were analyzed by TLC and the radioactivity distribution on the plates determined using the three techniques. Radioactivity scanning is appropriate only with good chromatographic resolution and previously validated scanning parameters. Film autoradiography exhibits poor linearity if radioactivity varies greatly. PSL provides high sensitivity and resolution and superior linearity compared with the other methods.

Aminopyridines↗
PubMed2005

Analysis of low level radioactive metabolites in biological fluids using high-performance liquid chromatography with microplate scintillation counting: method validation and application.

TopCount, a microplate scintillation counter (MSC), has been recently employed as an off-line liquid radiochromatographic detector for radioactive metabolite profile analysis. The present study was undertaken to validate TopCount for metabolite profiling with respect to sensitivity, accuracy, precision and radioactivity recovery. Matrix effects of various human samples on TopCount performance and capability of MSC for volatile metabolite analysis were also investigated. TopCount had a limit of detection (LOD) of 5 DPM and a limit of quantification (LOQ) of 15 DPM for [(14)C]-labeled compounds at a 10min counting time. It was two-fold more sensitive than a liquid scintillation counter (LSC), and 50-100-fold more sensitive than a radioactivity flow detector (RFD). TopCount had comparable accuracy and precision to RFD, and comparable precision to LSC for determining relative abundance of metabolites. Human liver microsome incubation (up to 1 mL), plasma (up to 1 mL), urine (up to 2 mL) and feces (up to 50mg) had no significant quenching effects on TopCount performance. Benzoic acid, a volatile metabolite, was detected by TopCount, but not by Microbeta counter after microplates were dried under vacuum. Radioactivity recovery in HPLC-MSC analysis was reliably determined using an LSC-based method. Examples of using HPLC-MSC for analysis of low levels of radioactive metabolites are presented, including determination of plasma metabolite profile, in vitro reactive metabolites trapped by [(3)H]glutathione, and metabolite concentrations in an enzyme kinetic experiment. The data from this study strongly suggest that HPLC in combination with TopCount is a viable alternative analytical tool for detection and quantification of low levels of radioactive metabolites in biological fluids.

Animals↗
PubMed1998

Reduction of radioactive seed embolization to the lung following prostate brachytherapy.

PURPOSE: Ultrasound-guided interstitial implantation of radioactive seeds is a common treatment for early stage prostate cancer. One of the risks associated with this therapy is seed embolization to the lung. This paper reports on the incidence and possible adverse effects of seed migration. METHODS AND MATERIALS: Two hundred ninety consecutive patients were treated with permanent radioactive seed brachytherapy for prostate cancer between January 1 and December 31, 1995. One hundred fifty-four patients were treated with iodine-125 (I-125), and 136 patients were treated with palladium-103 (Pd-103). All but one patient had a routine post implant chest radiograph (CXR), leaving 289 evaluable patients. RESULTS: Twenty radioactive seed pulmonary emboli were identified in 17 patients; 3 patients had two emboli each. The radioactive seed pulmonary embolism rate for the entire group of patients was 5.9%. Acute pulmonary symptoms were not reported by any patient in this series. One hundred forty-six study patients were implanted with free seeds alone (136 Pd-103 and 11 I-125), and 143 were implanted with linked seed embedded in a vicryl suture for the peripheral portions of their implants. The radioactive seed embolization rate by patient was 11% (16/146) versus 0.7% (1/143) for free seed implants and implants utilizing linked seeds, respectively. The difference was statistically significant, p = 0.0002. No patient had detectable morbidity as a consequence of seed emboli. CONCLUSION: The use of linked seeds embedded in vicryl sutures for the peripheral portion of permanent radioactive seed prostate implants significantly reduced the incidence of pulmonary seed embolization in patients treated with the Seattle technique.

Brachytherapy↗
PubMed2002

Vascular morphometric changes after radioactive stent implantation: a dose-response analysis.

OBJECTIVES: The goal of this study was to evaluate the dose-dependency of morphometric changes in the coronary arterial wall after radioactive stenting. BACKGROUND: Radioactive stents have been found to reduce intrastent intimal hyperplasia (IIH) but lead to a characteristic type of restenosis occurring predominantly at the stent edges. METHODS: Fifteen patients underwent intravascular ultrasound (IVUS) examination after implantation of a P-32 radioactive stent and at the six-month follow-up. The post-stent IVUS measurements on seven predefined locations of each lesion were subjected to a computer algorithm for the development of dose-volume histograms (DVH). Thus, we derived the radiation doses delivered to at least 10% and 90% of the adventitia (DV10, DV90). The IIH and vascular remodeling at follow-up were correlated with the doses in each segment. RESULTS: The IIH was most pronounced at the stent edges and lowest in the stent-body, whereas we detected a significant expansive remodeling within the stent body. The delivered doses correlated with a decreased IIH (r = 0.52, p < 0.001 for DV10 and r = 0.62, p < 0.001 for DV90) and with expansive remodeling (r = 0.48, p = 0.009 for DV10 and r = 0.50, p = 0.006 for DV90). A DV10 >90 Gy or a DV90 >15 Gy reduced IIH and induced expansive remodeling. Plaque growth was not reduced by radioactive stents. CONCLUSIONS: The DVH analysis reveals a dose-dependent increase of external elastic lamina area behind radioactive stents, whereas plaque growth is not reduced but inverted into an outward direction from the stent. A DV10 >90 Gy or a DV90 >15 Gy results in a beneficial long-term outcome after radioactive stenting.

Arteries↗
PubMed1999

Species difference in radioactivity elimination from liver parenchymal cells after injection of radiolabeled proteins.

To elucidate the cause for the different levels of hepatic radioactivity among mammals after injection of protein radiopharmaceuticals, the metabolism of radiolabeled proteins and the fate of their radiometabolites in the parenchymal cells of rat liver were investigated and compared with those of mice. We used galactosyl-neoglycoalbumin (NGA) as a carrier protein, and NGA was labeled with 111In via 1-(4-isothiocyanatobenzyl)ethylenediaminetetraacetic acid (SCN-Bz-EDTA) or 1-[p-(5-maleimidopentyl)aminobenzyl]ethylenediaminetetraacetic acid (EMCS-Bz-EDTA) and with 125I via direct iodination. All radiolabeled NGAs exhibited rapid accumulation in liver parenchymal cells after intravenous injection into rats. Radioactivity was eliminated following NGA-125I injection at similar rates from rat and mouse liver. In contrast, both 111In-labeled NGAs demonstrated much slower elimination of radioactivity in rat when compared with mouse liver. Analyses of radioactivity in bile and liver indicated that both SCN-Bz-EDTA and EMCS-Bz-EDTA rendered mono-amino acid adducts as the final radiometabolites, which were generated in rat liver within 1 h postinjection. Subcellular distribution studies suggested that these radiometabolites were copurified with lysosome in rat liver. Because similar results were observed in mice previously, the difference between rats and mice in radioactivity elimination from liver parenchymal cells would be predominantly attributable to the different efflux rate of the 111In-labeled metabolites from the lysosome between these species. Such differences in the efflux rates of radiometabolites from the lysosome among mammals may also account for the different hepatic radioactivity levels of radiolabeled proteins between animal and clinical studies.

Albumins↗
PubMedDate not supplied

Radioactivity as a significant energy source in prebiotic synthesis.

Radioactivity in the continental crust (due mainly to the isotopes 238U, 235U, 232Th and 40K), as a energy source for chemical evolution in the early Archean (between 3.5 and approximately 4 Ga bp), is reviewed. The most important radioactive source in the continental crust is due to the production and accumulation of radioactive gases within the crust voids (porosity). The study of such mechanism has allowed us to reach a deeper understanding about the nature of the radioactive source and to describe its behavior, particularly with regard to prebiotic chemical evolution. An effective total energy of 3 x 10(18) Ja-1 has been obtained for a depth of 1 km, 4 Ga ago. If a depth of 30 km is taken, the obtained value is almost equal to the UV solar energy radiation (lambda < 150 nm). Within the voids the radioactive source of the continental crust played a relevant role in prebiotic synthesis. In uranium deposits of the same age, the role of radioactivity must have been even more relevant in favoring chemical evolution.

Earth, Planet↗
PubMed2006

Proton-proton correlations observed in two-proton radioactivity of 94Ag.

The stability and spontaneous decay of naturally occurring atomic nuclei have been much studied ever since Becquerel discovered natural radioactivity in 1896. In 1960, proton-rich nuclei with an odd or an even atomic number Z were predicted to decay through one- and two-proton radioactivity, respectively. The experimental observation of one-proton radioactivity was first reported in 1982, and two-proton radioactivity has now also been detected by experimentally studying the decay properties of 45Fe (refs 3, 4) and 54Zn (ref. 5). Here we report proton-proton correlations observed during the radioactive decay of a spinning long-lived state of the lightest known isotope of silver, 94Ag, which is known to undergo one-proton decay. We infer from these correlations that the long-lived state must also decay through simultaneous two-proton emission, making 94Ag the first nucleus to exhibit one- as well as two-proton radioactivity. We attribute the two-proton emission behaviour and the unexpectedly large probability for this decay mechanism to a very large deformation of the parent nucleus into a prolate (cigar-like) shape, which facilitates emission of protons either from the same or from opposite ends of the 'cigar'.

Journal Article↗
PubMed1973

Control of synthesis and release of radioactive acetylcholine in brain slices from the rat. Effects of neurotropic drugs.

1. Studies of the synthesis and release of radioactive acetylcholine in rat brain-cortex slices incubated in Locke-bicarbonate-[U-(14)C]glucose media, containing paraoxon as cholinesterase inhibitor, revealed the following phenomena: (a) dependence of K(+)-or protoveratrine-stimulated acetylcholine synthesis and release on the presence of Na(+) and Ca(2+) in the incubation medium, (b) enhanced release of radioactive acetylcholine by substances that promote depolarization at the nerve cell membrane (e.g. high K(+), ouabain, protoveratrine, sodium l-glutamate, high concentration of acetylcholine), (c) failure of acetylcholine synthesis to keep pace with acetylcholine release under certain conditions (e.g. the presence of ouabain or lack of Na(+)). 2. Stimulation by K(+) of radioactive acetylcholine synthesis was directly proportional to the external concentration of Na(+), but some synthesis and release of radioactive acetylcholine occurred in the absence of Na(+) as well as in the absence of Ca(2+). 3. The Na(+) dependence of K(+)-stimulated acetylcholine synthesis was partly due to suppression of choline transport, as addition of small concentrations of choline partly neutralized the effect of Na(+) lack, and partly due to the suppression of the activity of the Na(+) pump. 4. Protoveratrine caused a greatly increased release of radioactive acetylcholine without stimulating total radioactive acetylcholine synthesis. Protoveratrine was ineffective in the absence of Ca(2+) from the incubation medium. It completely blocked K(+) stimulation of acetylcholine synthesis and release. 5. Tetrodotoxin abolished the effects of protoveratrine on acetylcholine release. It had blocking effects (partial or complete) on the action of high K(+), sodium l-glutamate and lack of Ca(2+) on acetylcholine synthesis and release. 6. Unlabelled exogenous acetylcholine did not diminish the content of labelled tissue acetylcholine, derived from labelled glucose, suggesting that no exchange with vesicular acetylcholine took place. In the presence of 4mm-KCl it caused some increase in the release of labelled acetylcholine. 7. The barbiturates (Amytal, pentothal), whilst having no significant effects on labelled acetylcholine synthesis in unstimulated brain except at high concentration (1mm), diminished or abolished (at 0.25 or 0.5mm) the enhanced release of acetylcholine, due to high K(+) or lack of Ca(2+). The fall in tissue content of acetylcholine, due to lack of Ca(2+), was diminished or abolished by pentothal (0.25 or 0.5mm) or Amytal (0.25mm).

Acetylcholine↗