Melatonin (MLT) secretion was examined in six normal pressure hydrocephalus (NPH) patients before and after ventriculoperitoneal (VP) shunt surgery. Ten healthy subjects were used as controls. Venous blood samples were taken daily at 2 p.m., 8 p.m., 2 a.m., and 8 a.m. Radioimmunoassay of MLT used a new specific antiserum and separation method achieving low cross-reactivity and high-efficiency MLT separation. Plasma levels in the control group at 2 p.m. and 2 a.m. were significantly different, showing diurnal rhythm (DR). The patients’ MLT levels before VP shunt were significantly lower than control levels and the DR was absent. Postoperatively, the values were significantly different from preoperative values only at 2 a.m., but the DR reappeared. Thus, in NPH, VP shunt surgery improved the melatonin DR, probably through normalization of the dilated third ventricle.
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