RESUMO
Mammals are homeotherms and expend considerable energy maintaining their body temperatures. The temperature of a mammalian embryo on the other hand is maintained by the mother and the embryo can devote its metabolic energy to growth and development. The mammalian embryo is acting as a poikilotherm and its energy needs are thus considerably less than if it were a comparably sized homeotherm. The energy requirements of the preimplantation rat embryo are generated by anaerobic metabolism. As it grows, aerobic metabolism develops. In culture, the addition of carbon monoxide to the perfusing gas for early rat embryos has a much smaller effect than decreasing the oxygen concentration. Carbon monoxide appears to be a relatively mild toxicant until the embryo is much larger, is depending much more on transport of oxygen by red blood cells, and the fraction of required metabolic energy produced by anaerobic metabolism has become quite small. The effect from smoking during gestation may be either by the concomitant reduction in food intake or a more direct toxic effect from some components in the smoke. Carbon monoxide does not seem to be the culprit. The possible mitigating effect of a compensatory increase in fetal hematocrit in response to any hypoxia must also be considered. Humans have no yolk sac placenta as rodents do, but if the switch from anaerobic to aerobic metabolism is correlated with the stage of development, then carbon monoxide exposure should not represent any significant risk to the human embryo until later in gestation.
Assuntos
Monóxido de Carbono/toxicidade , Embrião de Mamíferos/efeitos dos fármacos , Animais , Metabolismo Energético , Feminino , Idade Gestacional , Humanos , Troca Materno-Fetal , Consumo de Oxigênio , Gravidez , Fumar/efeitos adversosRESUMO
129I, a very long lived fission product, persisted in the environment after discharge from the chemical reprocessing plants at Hanford. The significance to human health is evaluated by considering the maximum possible impact it might have. Allowing the total production of 129I to be discharged to the air and considering the location where the maximally exposed individuals residue, the lifetime cumulative thyroid dose is calculated as a function of birth year. The maximally exposed individual at the maximum exposure location was born in 1954 and accumulates a thyroid dose between 1954 and 1995 of slightly over 9,000 microSv (900 mrem) at an average rate of 220 microSv (22 mrem) y-1. Over the same period of time, the soft tissue dose from background radiation due to both external and internal radiation is about 38,000 microSv (3,800 mRem).
Assuntos
Poluentes Radioativos do Ar , Exposição Ambiental , Contaminação Radioativa de Alimentos , Radioisótopos do Iodo , Leite , Glândula Tireoide/efeitos da radiação , Animais , Fenômenos Químicos , Química , Feminino , Humanos , Indústrias , Radioisótopos do Iodo/farmacocinética , Masculino , Matemática , Modelos Teóricos , População Rural , Caracteres Sexuais , Fatores Sexuais , Glândula Tireoide/metabolismo , Fatores de Tempo , Distribuição Tecidual , Urânio , WashingtonRESUMO
In December 1949, a large amount of 131I was released to the air at Hanford during the dissolving of irradiated uranium fuel for a classified military experiment called the "Green Run." Reports of the release have varied from about 0.15-0.3 PBq. Using, as a guide, the reported measurements of 133Xe released during the experiment, the amount of 131I released has been reanalyzed. The results indicate that about 0.40 +/- 0.12 PBq (11 +/- 3 kCi) was released, somewhat larger than the largest previous estimates.
Assuntos
Contaminação Radioativa do Ar/história , Radioisótopos do Iodo/história , Reatores Nucleares/história , Contaminação Radioativa do Ar/análise , História do Século XX , Modelos Químicos , Radiometria , Washington , Radioisótopos de Xenônio/históriaRESUMO
Rat embryos at days 11-12 of gestation cultured for 18 hours in vitro respond to reduced oxygen or to elevated levels of CO. Glucose consumption and lactate production increase while the growth rate decreases. The ratio of lactate produced to glucose consumed increases to values characteristic of earlier, more anaerobic, embryos. It is suggested that most of the energy consumed by the embryo goes to support growth and that the change in glucose metabolism results in a decrease in available energy which decreases the growth rate. The response to reduced oxygen levels is more marked than the response to elevated levels of carbon monoxide and we interpret the result to imply that oxygen transport in these embryos is primarily via solution rather than via combination with hemoglobin.
