Aim of the study: Was to investigate the differences of the cirrcadian rhythm of the endogenous somatostatin in patients with carcinoid and in healthy probands. Methods: The group of 30 patients (16 men/14 women) was divided onto two groups. The group M of 20 (12/8) pts with metastatic disease and group B of 10 pts without known metastases at the time of investigation. The control group A included by 12 healthy probands (7/5). Plasma levels of somatostatin were determined by radioimmunoassay. Fisher periodogram and Halberg's cosinor were used for statistical evaluation. Results: We confirmed the 24-bour cirrcadian rhythm of somatostatin in group A, B and M. Patients of the M group when compared with A and B groups had higher mesor and the later 24-bour acrophase (p < 0,05) and 12-bour acrophase (p < 0,05). Treatment with lanreotide led to the significant decrease of the somatostatin mesor (p < 0,05).

        Key words: carcinoid, cirrcadian rhythm of endogenous somatostatin, lanreotid