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PubMed1999

A schema for estimating absorbed dose to organs following the administration of radionuclides with multiple unstable daughters: a matrix approach.

The dosimetry of alpha particle emitters requires that all decays, including those of unstable intermediates be included in the calculation. Such calculations are complicated by the potential differential biologic distribution of each of the intermediates. In this work we present a formalism which will account for the known biodistribution factors of the daughters and the resulting effective biodistribution which will depend upon the site at which the parent radionuclide decays. The number of decays or cumulated activity of a daughter radionuclide present in a particular tissue is estimated using a probability matrix which describes the likelihood of daughter decay in a particular tissue as a function of the decay site of the parent. An example of three initial compartments is provided to illustrate the use of this formalism. Such modeling may be used to evaluate the feasibility of using radionuclides whose decay includes alpha-emitting intermediates. Model validation and refinement will require an assessment of the fate of free, alpha-emitting intermediates in various biological milieus.

Alpha Particles↗
PubMed1981

Apparent dualistic effects of twice daily melatonin administration on reproductive organs in male golden hamsters.

Daily subcutaneous injections of various dosages of melatonin were given early in the light phase to groups of adult male golden hamsters maintained in a long photoperiodic cycle (14 h light). This injection was followed by a second daily injection of melatonin late in the light phase at a concentration sufficient to induce reproductive organ atrophy. An afternoon injection of melatonin resulted in reproductive organ atrophy in animals that received 0, 1 or 5 microgram of melatonin in the morning. However, morning injections of 25 or 100 microgram of melatonin partially prevented the inhibitory effects of the afternoon injection of melatonin, and a morning injection of 500 microgram of melatonin prevented the reduction of testicular weights in animals which concurrently received the afternoon injection of melatonin. Serum testosterone levels were depressed in animals that received afternoon injections of melatonin regardless of the dosage of melatonin given in the morning. The greatest concentration of melatonin given in the morning (500 microgram) did not completely prevent the depressive effect of the afternoon injection of melatonin on serum testosterone. Since melatonin-induced gonadal atrophy is not prevented by a morning injection of melatonin of less than 25 microgram, the data suggest that there is a lower limit of the concentration of melatonin when given in the morning that is incapable of "down-regulating" the melatonin receptors to the atrophy-inducing injection of the indole given later in the photoperiod.

Animals↗
PubMed1976

[LD50 values and selenium concentration in rabbit organs after parenteral administration of sodium selenite and determination of toxicity of urososelevit pro inj].

The LD50-values of sodium selenite after i/m injection to rabbits was determined by means of probit-regression straight line. Simultaneously a combination of vitamin E and sodium selenite was tested for toxicity in order to examine the effect of vitamin E on the selenium toxicity. The LD50/24h was 2.53 mg sodium selenite/kg body mass and in combination with vitamin E (30 IU vitamin E/5 mg NaSeO3) 2.73 mg/kg. Furthermore the selenium concentration was determined in blood, liver, kidney and muscles of animals which died or were killed after 24 h respectively. Not only chemical analysis but also relations of time-dose-efficiency and significantly increased LD50-values show a certain protective effect of vitamin E on selenium intoxication.

Animals↗
PubMed1975

[LD 50 and selenium concentration in organs following intravenous administration of sodium selenite in the rabbit].

In experiments on 72 rabbits, the LD50 of sodium selenite by intravenous injection was found to be 2.24 mg/kg body weight. The clinical picture and pathological changes associated with acute selenium poisoning are described. The increase in selenium concentration was up to nine times the normal in liver and up to six times in kidney and muscle. There was no sign of a return to normal values 24 hours after administration.

Animals↗