Secretion of calcitonin and gastrin in rats with transplanted medullary thyroid carcinoma

Rats transplanted with medullary thyroid carcinoma (MCT) were followed with radio-immuno assay of serum calcitonin (iCT) using antisera to human CT and I125 labelled calcitonin-M. From the 4th month after transplantation, serum from the tumour rats contained iCT in concentrations 8-10 fold higher than serum from the control rats. The tumour cells had retained their ability to react on pentagastrin and calcium injections with increased CT release. It was further shown that the tumour bearing rats had elevated basal gastrin concentratkons in serum. While calcium injection lead to a rise in the serum gastrin concentration in the control group, the adverse effect was seen in the tumour bearing rats. The morphological features and the responsiveness of the rat tumour cells to physiological secretagogues make this tumour a suitable animal model for the study of interactions between CT and gastro-intestinal factors. It is suggested that the gastrin response to calcium might be of interest also in the diagnosis of human MCT.