Betsy J. Stover

The Incorporation of Various Metal Ions into in Vivo- and in Vitro-Produced Melanin

Small amounts of a number of metal ions have been found in melanins obtained from natural sources, and

Liver Injury in Beagles With Pu239: Distribution, Dosage and Damage

{}^{140}{\rm Ba}

The Distribution and Pathological Effects of Pu in Juvenile Beagles

and226 Ra have been found to deposit in tissues containing melanin. In the studies reported here, some aspects of the chemical nature of the incorporation were investigated with radionuclides of high specific activity. The uptake of metal ions by synthetic melanin from a physiological buffer increased with decreasing hydrated ionic radius, decreased with decreasing pH, and decreased in the presence of chelating agents. Replacement of melanin-bound

Some effects of long-term alpha irradiation on the composition and structure of bone.

{\rm Ra}^{++}

Delayed Effects of Bone-Seeking Radionuclides

with H+ demonstrated the reversibility of the reaction. Comparative studies with synthetic melanin and natural melanin plus its protein showed that the role of the protein in the reactions is small. Both the reaction characteristics and the chemical structures of melanin and of weak acid cation exchangers are similar, which suggests that metal ions and melanin interact by ion exchange.

RADIOBIOLOGY OF PLUTONIUM.

The livers of Pu239-injected beagles retained 15 to 30 per cent of the injected dose. Initially, autoradiographs showed a uniform distribution of alpha -activity. At 400 days postinjection, there was a focal distribution associated with condensed reticulum and reticulo-endothelial concentration. Subsequently, at the time of sacrifice 3 to 8 years postinjection, 80 to 85 per cent of the liver was replaced by regenerative nodules with no alpha -activity. The absence of hepatomas was in sharp contrast to the presence of osteogenic sarcomas in some dogs with comparable doses to bone and liver.

RADIATION-INDUCED BONE CANCER IN BEAGLES.

Twelve juvenile beagles 90 days old were injected intravenously with 2.8 ..mu..Ci /sup 239/Pu/kg. All attained normal skeletal size and normal weight. However, all died from osteosarcoma with an average survival time of 1306 +- 163 days after injection. At death the liver contained 12.7 +- 2% of the injected /sup 239/Pu, and less than 1% was in the total of kidneys, lung, and spleen. In a liver homogenate, free of nuclei and debris, most of the Pu was bound to ferritin in the cytosol or found with microsomes. No overt evidence of radiation-induced liver damage was discernible. At death, the juvenile skeletons contained 56.0 +- 3.1% compared to 44% in beagles injected as young adults. Highly active bone growth and turnover produced a skeletal redistribution pattern of Pu which differed from that observed in young adults. The cumulative average dose to the anatomical skeleton was 2850 +- 443 rad. Seventeen bone tumors were produced, located predominantly in areas with high concentrations of Pu and rapid bone turnover rates. Skeletal radiographs taken at death revealed 33 fractures, all of which had healed.

Effect of dose level on skeletal retention of /sup 239/Pu(IV) in the beagle

Comparison of selected skeletal samples from healthy adult beagles and beagles given about 3 μc Pu/sup 239//kg several years prior to sacrifice showed significant differences in relative water, organic, and inorganic contents but not in the relative amounts of calcium and phosphate in bone mineral. These differences correlate with histological and microradiographic observations of changes in cellularity, hypo-, and hypermineralization, and loss of osseous tissue. A few changes in relative bone composition with age were observed.