Expression of gastrointestinal endocrine tumours in culture systems.

Human endocrine tumours were studied in in vitro systems (cell suspensions and tissue cultures) and in in vivo systems (tumour transplants to the anterior eye-chamber of immunosuppressed rats). In the experimental systems the tumour cells were demonstrated to synthesize and secrete the same hormonal products as in the patient. Intraocular transplants of a gastrinoma secreted gastrin-17 into the chamber fluid. This molecule, normally not secreted in the rat, was also detected in the peripheral plasma of tumour-bearing rats. Intraocular transplants of midgut carcinoid tumours released serotonin (5-HT) at adrenoceptor stimulation, of a similar type as demonstrated in acute tumour cell suspensions. However, in tissue cultures genuine beta-adrenoceptors seemed to be modified, since pretreatment with beta-adrenoceptor antagonists or calcium deprivation did not prevent stimulated 5-HT release. Tachykinins were not liberated by adrenoceptor stimulation. In certain cultures of midgut carcinoid tumour cells, two different phenotypes developed: small rounded endocrine tumour cells with positive immunoreactions against 5-HT and tachykinins (TK), and large elongated neuron-like cells, which gradually lost 5-HT immunoreactivity, while TK immunoreactivity remained unchanged. These cultured tumour cells may produce an endogenous factor inducing transformation into a neuron-like phenotype. One candidate factor is nerve growth factor (NGF), since NGF-like immunoreactivity was demonstrated in cells of the endocrine phenotype.