Impaired nocturnal synthesis of melatonin in patients with cardiac syndrome X.

We investigated nocturnal secretion pattern of melatonin in patients with cardiac syndrome X and healthy subjects. The present study performed in five patients with cardiac syndrome X and in nine healthy controls. Blood samples from all subjects were collected every 2 h intervals between 22:00 and 08:00 h. Melatonin levels were measured with a radioimmunoassay kit. Patients with cardiac syndrome X secreted less nocturnal melatonin at 02:00 h than control subjects (P=0.04). Peak and Delta melatonin (peak-lowest melatonin) were found lower in patients with cardiac syndrome X (P=0.039 and P=0.028, respectively). In conclusion patients with cardiac syndrome X show a markedly decreased nocturnal melatonin synthesis. Our study provides useful information about melatonin synthesis and release in patients with cardiac syndrome X might help physicians in managing these patients.