Cyclic AMP and adenyl cyclase in brain tumors

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Abstract
Some of the regulatory mechanisms of cyclic[c]AMP production in human brain tumors were investigated by assessing cAMP levels and adenyl cyclase activity. A large disparity was found between the levels of cAMP of normal brain and brain tumor tissue. CAMP levels were lower in brain tumors (25.8 pmol/mg protein) than in normal brain (98.8 pmol/mg protein). These studies also show that the abnormally low levels of cAMP in tumors parallel those of adenyl cyclase. The mean adenyl cyclase activity of brain tissue was 111.0 pmol of cAMP/min per mg protein, while that of the tumor was only 23.0 pmol/min per mg protein. Levels of cAMP and adenyl cyclase activity were inversely related to the degree of malignancy. Attempts to stimulate adenyl cyclase in homogenates of human brain and brain tumors resulted in a similar response in both tissues. Norepinephrine was the most effective stimulant and produced a 2 to 3-fold increase in cAMP production, while histamine had no effect. One of the factors governing tumor growth may be a defect in the adenyl cyclase system.