Amine handling properties of human carcinoid tumour cells in tissue culture.

Carcinoid tumour tissue from two patients was removed from lymph node metastases during surgery. Under sterile conditions the cells were prepared for tissue culture, and grew in clusters for a period of 3-4 weeks. Using immunofluorescence the neoplastic cells were investigated for the presence of various antigens characteristic for other amine handling cell types (adrenal medullary cells, adrenergic neurons, endocrine cells); thus, the presence of catecholamine synthesizing enzymes, 5-HT, MAOs, neuron specific enolase, synaptophysin, chromogranin A and neurofilaments was demonstrated in the carcinoid tumour cells. Also ?-adrenoceptor-like immunoreactivity was present, as was NGF-like immunoreactivity. The amine handling properties were investigated by measuring spontaneous and drug-induced release of 5-HT into the culture medium. Reserpine enhanced the 5-HT levels in the medium, and this was further potentiated by the MAO-inhibitor nialamide or the membrane pump blocker imipramine. The 5-HT synthetic capacity was pronounced, as indicated by measuring the cumulative 5-HT release into the medium after frequent changes of media (at 1 h intervals). If media were changed every 4 d 5-HT levels reached a saturation. In the fluorescence microscope the effect of reserpine in depleting the 5-HT stores was slow; at 24 h of reserpine presence in the media many cells still contained strong 5-HT fluorescence (partly with an agranular appearance) while some cells appeared depleted. Thus, there was a striking difference between individual cells in the reaction to reserpine. ?-Adrenoceptor activation with isoprenaline released 5-HT into the medium in a dose-dependent manner, not blocked by propranolol. This indicates unusual properties of the ?-adrenoceptor, also demonstrated to be present on these neoplastic cells by immunocytochemistry.