Agnes N. Stroud

Toxicity of Tritium Oxide to Mice

Summary The 30-day median lethal dose of H3 2 for CF No. 1 female mice is about 1 mc per g body weight when given in a single injection. The estimated radiation dosage is about 800 rep in the first 3 days and about 1000 rep in the first 12 days after injection. It is concluded that no unexpected factor of biological effectiveness exists for tritium β rays in relation to X or γ rays.

QUANTITATION OF CELLULAR RESPONSES IN THE MOUSE SPLEEN AFTER IRRADIATION

Following sublethal whole-body irradiation of young mice, the spleen diminishes in size in relation to dose, then hypertrophies so that after larger doses it much exceeds the original weight. This reflects a very much more rapid regeneration at higher doses than occurs at lower doses. This regeneration takes place largely in proliferating areas within the red pulp. This proliferation is in some cases grossly nodular and in others it is not. When nodules are seen, when they appear, they are fewer and more rapidly growing after higher radiation doses. If those were taken to resemble a survival curve of single colony-forming units, an original population of somewhat more thand 100 such units would be indicated. Further work is required to establish whether such a mechanism is active. (auth)

Scanning Electron Microscopy of Cells

The scanning electron energy-analyzing microscope uses characteristic energy losses to provide picture contrast. At different levels of energy loss particular structures are distinguished with high contrast in an unstained section of a cell.

Formation of giant nuclei in continuously irradiated tumors

SummaryTransplantable malignant tumors of mice and rats have been irradiated continuously for several days by means of embedded glass beads containing Sr90-Y90. Concomitant enlargement of tumor cell nuclei occurs in areas where mitosis is inhibited, i.e. associated with doses of 1200–2000 rads per day and above. Some enlarged cells survive at least a week in areas where the dose rate is much higher than this. Intense incorporation of thymidine into enlarged cells can be seen at least a week after beginning irradiation.

DNA synthesis in mammalian kidney cells in tissue culture after single and periodic doses of irradiation.

Introduction Several studies have been made of the ability of cells in vitro to synthesize DNA after single doses of irradiation, but little is known about the DNA synthesis of cells after repeated doses. Some investigations have shown that DNA synthesis is inhibited following irradiation others have shown an appreciable The present communication will show a marked difference in the ability of two mammalian kidney cell lines from unrelated species and of different chromosome number to utilize tritiated thymidine in the synthesis of DNA, both under normal conditions and following single or periodic exposures to X irradiation. Thymidine uptake was measured in a near-tetraploid rhesus monkey kidney cell line and in a diploid pig kidney cell line. The tissue culture has certain advantages in tracer studies over whole animal tissue or tissue slices in that it is a preparation of a single cell type, growing as a monolayer on a glass surface; thus experimental interpretation is not subject to the complications that are encountered using a tissue containing many cellular types, possibly of different radiosensitivities. Radiation dosimetry to the cells is more readily calculated under these conditions. Availability of labeled compounds to cells growing in vitro is insured, the specific activity of the pool from which a tracer is incorporated is measurable, and unincorporated label is easily accountable by recovery. Cells can be maintained continuously under controlled nutritive conditions, and morphological studies are easily paraIleled with tracer studies. We present data showing that in tissue culture an established monkey kidney cell line utilizes tritiated thymidine a t a very low rate, that the rate of uptake is materially increased after irradiation, and that pig kidney cells behave in a very different manner.