Tissue radiolabeled

Cells or tissue Radiolabeled precursor Retinoid" Reference... 

The nonquantitative detection of radioactive emission often is required for special experimental conditions. Autoradiography, which is the exposure of photographic film to radioactive emissions, is a commonly used technique for locating radiotracers on thin-layer chromatographs, electrophoresis gels, tissue mounted on sHdes, whole-body animal sHces, and specialized membranes (13). After exposure to the radiolabeled emitters, dark or black spots or bands appear as the film develops. This technique is especially useful for tritium detection but is also widely used for P, P, and 1. 

Following single dermal applications of 10 mg/kg of radiolabeled methyl parathion to pregnant rats, methyl parathion was found to be widely distributed to all major tissues and organs. Concentrations were highest in plasma and kidney, maximum levels measured 2 hours postapplication. Peak levels in liver, brain, fetus, and placenta, were measured 2 to 10 hours later, at which times the highest concentration of methyl parathion was in the fetus (Abu-Quare et al. 2000). 

In a study of pregnant rats that were exposed to radiolabeled methyl parathion by single dermal application, half-life elimination rate constants for various tissues ranged from 0.04 to 0.07 hour, highest values noted in plasma, kidneys, and fetus. Of the applied radioactivity, 14% was recovered in the urine in the first hour postapplication. By the end of the 96-hour study, 91% of the applied dose had been recovered in the urine. Fecal excretion accounted for only 3% of the administered dose (Abu-Qare et al. 2000). 

Three animal studies were located regarding distribution of endosulfan in animals following dermal exposure (Dikshith et al. 1988 Hoechst 1986 Nicholson and Cooper 1977). Endosulfan was detected in the brain (0.73 ppm), liver (3.78 ppm), and rumen contents (0.10 ppm) of calves that died after dermal exposure to a dust formulation of endosulfan (Nicholson and Cooper 1977). Following a single dermal application of aqueous suspensions of 0.1, 0.83, and 10.13 mg/kg C-endosulfan to male Sprague-Dawley rats, low concentrations of endosulfan (ng/g levels) appeared in the blood and tissues (other than skin at and around the application site) after 1 hour (Hoechst 1986). The concentrations of endosulfan in the blood and tissues increased with the time of exposure and were proportional to the dose applied. The liver and kidney appeared to sequester radiolabel relative to the concentrations of radiolabel in the blood or fat. Endosulfan levels were approximately 10 times higher in the liver and kidney than in the fat, blood, and brain throughout the study (Hoechst 1986). 

The results of metabolism studies with laboratory animals and livestock indicate that endosulfan does not bioconcentrate in fatty tissues and milk. Lactating sheep administered radiolabeled endosulfan produced milk containing less than 2% of the label. Endosulfan sulfate was the major metabolite in milk (Gorbach et al. 1968). A half-life of about 4 days was reported for endosulfan metabolites in milk from survivors of a dairy herd accidentally exposed to acutely toxic concentrations of endosulfan endosulfan sulfate accounted for the bulk of the residues detected in the milk (Braun and Lobb 1976). No endosulfan residues were detected in the fatty tissue of beef cattle grazed on endosulfan-treated pastures for 31-36 days (detection limits of 10 ppm for endosulfan, 40 ppm for endosulfan diol) the animals began grazing 7 days after treatment of the pastures. Some residues were detected in the fatty tissue of one animal administered 1.1 mg/kg/day of endosulfan in the diet for 60 days. No endosulfan residues were... 

Tamplin et. al. (54) observed that V. cholerae and A. hydrophila cell extracts contained substances with TTX-like biological activity in tissue culture assay, counteracting the lethal effect of veratridine on ouabain-treated mouse neuroblastoma cells. Concentrations of TTX-like activity ranged from 5 to 100 ng/L of culture when compared to standard TTX. The same bacterial extracts also displaced radiolabelled STX from rat brain membrane sodium channel receptors and inhibited the compound action potential of frog sciatic nerve. However, the same extracts did not show TTX-like blocking events of sodium current when applied to rat sarcolemmal sodium channels in planar lipid bilayers. 

Van Emon et al. ° developed an immunoassay for paraquat and applied this assay to beef tissue and milk samples. Milk was diluted with a Tween 20-sodium phosphate buffer (pH 7.4), fortified with paraquat, and analyzed directly. Fortified paraquat was detected in milk at less than 1 pgkg , a concentration which is considerably below the tolerance level of 10 pg kg Ground beef was extracted with 6 N HCl and sonication. Radiolabeled paraquat was extracted from ground beef with recoveries of 60-70% under these conditions. The correlation coefficient of ELISA and LSC results for the ground beef sample was excellent, with = 0.99, although the slope was 0.86, indicating a significant but reproducible difference between the assays. 

In animals, diisopropyl methylphosphonate absorbed from the gastrointestinal tract is rapidly distributed to the tissues as indicated by the decay in peak plasma levels after absorption (Hart 1976 Ivie 1980). In mice, plasma radioactivity declined slowly from 15 minutes to 1 hour after exposure and then dropped rapidly during the next 2 hours. At the end of 24 hours, the label in the blood was 0.63 g/mL or 0.3% of the 173- g/mL peak concentration (Hart 1976). The radiolabel in the plasma of rats after 24 hours was nearly identical to that in mice (0.61 g/L) and was 0.4% of the peak concentration. Clearance of label was slower in dogs with 1.3% of the 276- g/L peak concentration present after 24 hours. 

Tissue levels of diisopropyl methylphosphonate radiolabel in dogs were determined at 4 and 24 hours on the day of compound administration (Hart 1976). When the liver, kidney, and bladder values for dogs at 4-hours are compared to those for mice and rats, it appears that clearance from the body is slower in... 

Fat tissues do not appear to highly concentrate diisopropyl methylphosphonate or its metabolites. Tissue blood ratios for adipose deposits range from 1.3 to 3.6 in the species studied (Hart 1976). There was a surprisingly high concentration of radiolabel in the skin for mice with a tissue blood ratio of 14.6 (Hart 1976). It has been suggested, however, that the skin samples were contaminated with urine. 

In a single-dose oral study in male and female rats (Bucci et al. 1992), only 0.5% of the radioactivity from a dose of 660 mg/kg [14C]-radiolabeled diisopropyl methylphosphonate was found in the tissues 120 hours after dosing. The investigators indicated that no important tissue depot for diisopropyl methylphosphonate or its metabolites could be identified from the data obtained. 

The study of diisopropyl methylphosphonate distribution in a lactating Jersey cow was the only study that used multiple doses of diisopropyl methylphosphonate (Ivie 1980). In this single cow, radioactivity was detected in the blood 2 hours after dosing with [14C]-radiolabeled compound but not in the tissues. The animal had received diisopropyl methylphosphonate in one gelatin capsule for 5 days before the radiolabeled dose was administered. If tissue uptake in the cow was similar to that in dogs, measurements made 2 hours after dosing may not have provided an opportunity to measure tissue uptake of label. After 24 hours, 0.1% of the administered label was found in the cow s milk (Ivie 1980). 

There may be some hydrolysis of IMPA to MPA in the liver or in other tissues, but the MPA that is liberated is apparently bound to other molecules and is not immediately excreted. Most of the IMPA is rapidly removed from the blood by the kidneys and excreted by way of the urinary bladder. In mice, the concentrations of radiolabel in the empty urinary bladder from a single 225-mg/kg dose were greater than 1,000 g/mL in all samples taken between 30 minutes and 4 hours after compound administration (Hart 1976). In rats, concentrations of the label were 1,000 g/mL or greater for all measurements taken between 2 and 6 hours after dosing (Hart 1976). 

Donald JM, Cutler MG, Moore MR. 1986b. Effects of lead in the laboratory mouse 1. Influence of pregnancy upon absorption, retention, and tissue distribution of radiolabeled lead. Environ Res 41 420-431. 

The rapid turnover rate of some enzymes allows ELISAs to be designed that surpass the sensitivity of radiolabeling techniques. In addition, substrates can be chosen to produce soluble products that can be accurately quantified by their absorbance or fluorescence. Alternatively, substrates are available which form insoluble, highly colored precipitates, excellent for localizing antigens in blots, cells, or tissue sections. The flexibility of enzyme-based assay systems makes the chemistry of enzyme conjugation one of the most important application areas in bioconjugate techniques. 

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