Animals will be irradiated throughout the coming year to maintain a pool of intestinal tumor-bearing rats. The cAMP phosphodiesterase (PD) activities of tumor tissue will be further characterized. This will involve the subcellular localization of the enzymes followed by their publication. The kinetic parameters will then be measured in order to verify that preliminary results were correct and that, in fact, there is only a single PD in the intestinal cancer while normal intestinal cells have two PD enzymes. The cAMP synthetic activity of tumor tissue will be measured. It will then be possible to determine which ppthway in the cell is responsible for the lower cAMP concentration found in tumor tissue. The responsiveness of the synthetic activity of the adenylate cyclase to stimulation will be defined. The significance of the intracellular nucleotide concentrations in the lymphocytes from normal and tumor-bearing rats will be investigated further. Correlations between cyclic nucleotide concentrations in the tumor and degree of lymphocyte cytotoxicity to cancer cells in culture will be made when possible.