2 and American Medical Center at Denver*2 Sodium pentobarbital was injected in controls and the mice with spontaneous tumor. The mice were sacrificed at 5, 10, 15, 20, 25, and 30min after the injections and the levels of active pentobarbital were measured in the brains and plasma of both groups. The levels of unmetabolized pentobarbital in the tumor-bearing mice in both brain tissue and plasma were higher than in the controls, suggesting an impaired metabolism in the tumor-bearing mice

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... in quantitatively higher levels of active pentobarbital. However, the mice in both groups, tumor-breaing and control, wake up at the same level of active pentobarbital in the brain. In the tumor-bearing animals, it takes the active pentobarbital a little longer to reach that level and hence the prolonged sleeping time. The conclusions drawn from this study are: 1) There is an impaired metabolism of pentobarbital in tumor-bearing mice possibly caused by a tumor secretion such as toxohormone. 2) The possibility of an increased sensitivity of the brains of tumor-bearing mice to pentobarbital seems remote. 3) The possibility of increased blood-brain permeability due to the presence of a tumor also seems remote.