Carcinoid tumour cells in long-term culture: release of serotonin but not of tachykinins on stimulation with adrenoceptor agonists.

Tumour cells from a lymph-node metastasis of a midgut carcinoid tumour, immunoreactive for serotonin and substance P, were isolated and kept in culture for 2 months. The formation of large clusters or islets of tumour cells was paralleled by an increase in immunoreactive tachykinins (neuropeptide K and substance P) in the culture medium. The concentration of tachykinins declined subsequently despite good viability of the cells. Spontaneous release of serotonin into the culture medium was much greater than that of tachykinins, and remained stable throughout the study. These findings indicate different turnover rates and/or different storage sites for the peptides and the amine. In stimulation experiments, a dose-dependent release of serotonin, but not of tachykinins, was induced by a beta-adrenoceptor agonist (isoprenaline), while stimulation of alpha-adrenoceptors (noradrenaline) was not effective in releasing any of the substances. Pretreatment of the cultures with a beta-adrenoceptor antagonist (propranolol) or stimulations after calcium deprivation did not influence the isoprenaline-induced release of serotonin. These findings may indicate a modification of genuine beta-adrenoceptors during culture.