Apparatus has been developed for the irradiation of V79-379A Chinese hamster lung fibroblast cells with 3.6 MeV protons from the Van de Graaff accelerator at the National Accelerator Centre in Faure. The original intention of this work was to investigate and measure a possible dose rate effect on the survival of V79 cells, in the dose range from zero to 25 Gy, at dose rates of about 3 Gy/s and 300 Gy/s. The survival curves initially obtained were anomalous in that they showed abnormally high levels of survival and a tendency to remain at a constant survival level for doses above 10 Gy. Systematic attempts to correct this observed anomaly, involved the following; apparatus improvements were made, a means of measuring the beam profile was devised, the current measuring device and the dosimetry were improved and a possible dose rate effect on intracellular oxygen was investigated. After these improvements, the anomalous effect was much reduced, but not entirely eliminated. The final results showed no significant difference between the survival of cells irradiated at dose rates of about 3 Gy/s and 300 Gy/s; qualitative differences were however noticeable. After correction for the effect of a non-uniform beam profile, the survival curves were significantly different to published work. This difference suggested a possible dose rate effect between dose rates of about 0.1 Gy/s and dose rates above 3 Gy/s.

The major findings of this investigation are that polyamine biosynthetic enzymes and polyamine levels are regulated by specific cellular growth factors. A serum-free defined medium was developed for the Chinese hamster ovary cell line to examine the regulation of ornithine decarboxylase (ODCase) (EC.4.1.1.17), S-adenosylmethionine decarboxylase (SAMDCase) (EC.4.1.1.50), as well as polyamine catabolism. The activity of ODCase is dependent primarily on the presence of insulin, and appears to be modulated by transferrin and ferrous sulfate, indicating that iron transport may be important in the expression of ODCase activity. The enzyme activity can also be increased by depriving the substrate ornithine, which probably acts through a putrescine mediated event. This substrate limitation leads to an intracellular decrease in putrescine and spermidine, but not spermine. The activity of SAMDCase is not influenced by alterations in the growth factors or by ornithine deprivation. Since the spermidine levels are lower as compared to cells growing in medium with serum, it appears that SAMDCase activity is not generally regulated in a negative manner by spermidine. The polyamine interconversion enzymes, such as spermidine/spermine N¹-acetyltransferase and polyamine oxidase, appear to be regulated by growth factors other than insulin, transferrin, and ferrous sulfate. Cells maintained in defined medium are much more tightly attached to the surface of the dishes in which they are growing, which may be related to the growth factors present or a lack of cellular polyamines. Vinculin, a cell surface protein associated with focal adhesion plaques, moves away from the cell surface and into the nuclear area in defined medium cells as evidenced by fluorescent antibody staining. The major conclusions of this work are that ODCase synthesis is regulated by growth factors, that enzyme activity is also regulated post-transcriptionally by substrate and end-product, and that general polyamine metabolism is dependant on complex growth factors, other than insulin, which regulate the metabolism is dependant on complex growth factors, other than insulin, which regulate the metabolism and interconversion of polyamines.