Calcitonin production by rat thyroid tumours.

Immunolocalization techniques have been used to study 16 rat thyroids containing C cell tumours and ten rat thyroids in which no tumours or hyperplasias were found. All rats in these groups were at least 2 years old. An indirect ('sandwich') technique was used which involved rabbit or goat anti-human calcitonin antiserum and either fluorescein or peroxidase-labelled anti-rabbit or anti-goat IgG. Plasma calcitonin levels were measured in these animals and ina further group of ten young normal rats by means of an immunoradiometric assay using goat antiserum against synthetic human calcitonin. Both normal C cells and C cell tumours showed either apple-green fluorescence or positive peroxidase staining. The intensity of staining in the tumours vaired from one cell to another but was ingeneral less than that found for normal C cells. Calcitonin in the blood was detectable in most animals. The mean concentration found in young normal animals was 265 pg/ml (range less than 100-600 pg/ml), in old normal animals 160 pg/ml (range less than 100-400 pg/ml) and in rats with small C cell tumours 470 pg/ml (range 100-1200 pg/ml). The mean concentration in this latter group differed significantly from those of both normal groups (P less than 0-05). One animal with an invasive C cell tumour had a greatly increased calcitonin concentration (greater than 5 ng/ml) in the circulation. The results showed that calcitonin was present in normal rat C cells and that C cell tumours both contained and secreted calcitonin, underlining the similarity between these tumours and human medullary carcinomata.