Properties of Adenylate Cyclase of Lymphoid Cells

Adenylate cyclase of homogenates or lysates of mouse and rat lymphoid tissues was activated by the addition of fluoride ion, epinephrine, or norepinephrine, but not by any of several other hormones. The catecholamine stimulation was characterized as β-adrenergic. This activity was localized in the small lymphoid cells, was greater in thymic than in splenic or mesenteric node cells, and also was greater in mouse than in rat cells. Catecholamine-stimulated activity of mouse thymocytes remained constant from the 17-19th day of fetal development to 5 weeks after birth; it subsequently decreased to about one-half of the activity by 7-8 weeks. Similar decreases with age occurred in mouse spleen and rat thymus. In contrast, the glucagon-stimulated activity of rat liver increased during a similar period. Hypophysectomy of rats at 3 weeks did not influence the amount of cyclase activity of thymocytes assayed at 7 weeks. When intact mouse thymocytes were first incubated in a culture medium at 37°C with epinephrine or norepinephrine, a second addition of catecholamine after cell lysis no longer stimulated the enzymes. This loss of stimulation was selective, since basal activity and stimulation by fluoride ion were not affected. Incubation of intact cells with phytohemagglutinin markedly decreased the activity of lysates, whether assayed in the presence or absence of catecholamine or fluoride. In contrast, phytohemagglutinin added directly to the assay had no effect. No alternations occurred in adenylate cyclase activity as a result of the incubation of a 1:1 mixture of thymocytes from two strains of mice selected for the capacity of the cells to produce a mixed lymphocyte response.