The Effects of Cranial Irradiation on Platelet Monoamine Oxidase in Brain Tumor Patients
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The activity of monoamine oxidase (MAO) in human blood platelets provides an index of the state of activity of the monoamine system in the central nervous system. To understand the effects of cerebral radiotherapy on intracerebral monoamine metabolism, blood platelet MAO activity in ten patients with brain tumors was tested before and after administration of 10, 20, and 30 Gy irradiation. The control group consisted of 15 patients with malignancies other than brain tumor who had undergone radiotherapy: five with pelvic tumors, five with mediastinal tumors, four with cervical tumors, and one with a tumor in the axilla. The blood platelet MAO activvty of these patients was also tested before and immediately after 10, 20, and 30 Gy irradiation. Platelet-rich plasma obtained from venous blood was used to test the blood platelet MAO activity. An RI method was employed using tyramine as the substrate. The results are presented in units of disintegrations per minute (dpm) relative to the number of platelets. The patients who received cerebral irradiation and the control group, who received mediastinal and pelvic irradiation, showed the greatest decline in the number of blood platelets after 20 Gy irradiation. Irradiation of the neck or axilla, where red bone marrow is sparsely distributed, only slightly decreased the number of blood platelets. This implied that the decrease in the number of platelets depends on the amount of red bone marrow irradiated. Irradiation did not change blood platelet MAO activity in the control group. In the cerebral irradiation group, blood platelet MAO activity increased 40% after 20 Gy irradiation and 60% after 30 Gy. These increases were significant (p<0.01) compared to the MAO activity before irradiation. In both groups, blood platelets in the vascular bed were irradiated. A notable increase of blood platelet MAO activity after irradiation was observed only in the cerebral radiation group. This might be explained by its reflection of the change in the intracerebral amine metabolic system. The results suggest that cerebral irradiation which is focused on the region to be treated may eventually influence the mental state of a patient by affecting the intracerebral monoamine metabolism, especially serotonin.
- The Showa University Journal of Medical Sciences
The Showa University Journal of Medical Sciences 3(2), 117-124, 1991
The Showa University Society