Comparative study of different methods for the activity quantification of (3)H and (14)C radionuclides in dual labeled samples using liquid scintillation analyzer.

Different methods such as full spectrum DPM (FSDPM), dual isotope estimation and inclusion methods were studied for the activity quantification of (3)H and (14)C in dual beta labeled samples using liquid scintillation analyzer. A standardized Packard tritiated water was used as tritium source and (14)C activity was standardized by CIEMAT/NIST method and compared with the results obtained by the above three methods. Minimum detectable activity was 2100dpm/l for (3)H and 1200dpm/l for (14)C with a counting time of 300min. The accuracy of the results obtained was found to be within +/-10% for (3)H: (14)C activity ratios 1:1, 1:2, 2:1, 6:1, 9:1, 13:1 and 18:1.

Determination of 243Am by pulse shape discrimination liquid scintillation spectrometry.

Alpha specific activity of 243Am was determined using pulse shape discrimination in liquid scintillation spectrometry. 238Pu, 36Cl and 239Np (purified from 243Am) were used for obtaining the spillover of alpha/beta particles into the beta/alpha channels, respectively. Synthetic mixtures of 241Am/243Am were prepared. Using the alpha-specific activity, weights of the stock solutions used and the half-life of 241Am and 243Am isotopes, the expected 241Am/243Am atom ratios in the mixtures were determined and compared with those obtained by thermal ionization mass spectrometry (TIMS). An agreement of about 1% was obtained between the 241Am/243Am atom ratios determined by the two methods. This shows that liquid scintillation counting with pulse shape discrimination can be used for 243Am determination with an accuracy better than 1%.

Natural tritium levels in tender and ripe coconut fruit (Cocos nucifera L.): a preliminary examination.

Tissue Free Water Tritium concentrations (TFWT) were determined in tender coconut (Cocos nucifera L.) water, ripe coconut water, and kernel milk water, and compared with the same in groundwater collected from the vicinity of the trees. Samples with a very low tritium content were enriched by the alkaline electrolysis method. All of the samples were analyzed for tritium content in an ultra-low level liquid scintillation spectrometer. The TFWT in kernel milk water was found to be approximately 20-40 times higher than that in the groundwater. The tritium concentration in descending order in these samples is: kernel milk water, ripe coconut water, tender coconut water, and groundwater. The concentration of tritium increases as the fruit grows and the significantly high concentration in the kernel milk water suggests enrichment during the growth of the fruit.

Evidence for an early free radical-mediated reperfusion injury in frostbite.

Frostbite is characterized by acute tissue injury induced by freezing and thawing. Initial complete ischemia is followed by reperfusion and later, tissue necrosis. These vascular events support the hypothesis that free radical-mediated reperfusion injury at thawing might contribute to tissue necrosis after frostbite in a manner similar to that seen after normothermic ischemia. To test this hypothesis, rabbit ears were frozen at -21 degrees C for 30, 60, 90, or 120 s and rewarmed at room temperature (22 degrees C). Rabbits were treated "blindly" with saline alone, highly purified, pharmaceutical grade superoxide dismutase (SOD), allopurinol, or deferoxamine. The area of ear necrosis was determined 3 weeks after frostbite by "blinded" morphometry. The administration of SOD at the time of thawing significantly improved viability in ears frozen for 60 and 90 s, but not in those frozen for 30 or 120 s. Deferoxamine also improved viability in ears frozen for 60 s. Allopurinol did not significantly affect ear survival. Electron micrographs showed the appearance of severe endothelial cell injury beginning during freezing and extending through early reperfusion. Later, neutrophil adhesion, erythrocyte aggregation, and microvascular stasis were seen. These findings suggest that free radical-mediated reperfusion injury has a role in frostbite, and quantitate the proportion of the injury that is due to this mechanism.

Improved survival in free skin flap transfers in rats.

We have demonstrated previously that oxygen-derived free radicals are important mediators of tissue injury in experimental island skin flaps that have been subjected to prolonged ischemia (vascular occlusion) followed by reperfusion. In this study the role of oxygen free radicals in ischemia/reperfusion injury has been investigated in free flap transfers. Groin skin flaps were harvested, stored at room temperature for 21 to 24 hours, and transplanted to the contralateral groin. These free flap transfers normally exhibit a high incidence of complete necrosis. Treatment before the onset of reperfusion with a single dose of superoxide dismutase (SOD), a scavenger of superoxide radicals, increased the survival rate of these skin flaps from 38% in the control group to 76% (p less than 0.025). Tissue levels of SOD were measured before ischemia, after ischemia but before reperfusion, and 30 minutes after reperfusion: untreated flap tissues, which were destined to undergo necrosis, exhibited a significant decrease in SOD activity after reperfusion, whereas SOD-treated flap tissues, destined to survive, demonstrated increased enzyme activity. High levels of tissue SOD activity thus appeared to be associated with improved flap survival. The results have significant clinical implications with regard to organ preservation and transplantation.