It is known that tumours of several endocrine glands can be induced by a combination of a physiological stress and radiation. It was decided to assess the effect of radiation and of changes in dietary calcium on the development of thyroid tumours in the rat. Three hundred rats were given either 0, 5 or 10 \g=m\Ci of 131I in their first day of life. Each of these groups was subdivided after weaning, and maintained on a diet that was either high, normal or low in calcium. The animals were killed at intervals up to 27 months of age, and the numbers of thyroid tumours recorded. Follicular tumours were first noted at 9 months of age, and their frequency increased steadily with age. The effect of radiation was highly significant, only one tumour occurred in a non-irradiated animal. There was a small increase in frequency in follicular tumours in the high calcium diet group as compared to the low calcium diet group. C cell tumours were first noted at 9 months of age, and their incidence again increased with age. Significantly more tumours occurred in the radiated than in the non-irradiated animals. No significant variation occurred in relation to dietary calcium. It is concluded that an increase in dietary calcium, known to be mildly goitrogenic, may also be important in the carcinogenesis of follicular but not C cell tumours, and that radiation, known to be carcinogenic for thyroid follicular cells is also carcinogenic for C cells.
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.
1. The observation that thyroid C cell hyperplasia occurred in rats given the iron-deficient diet described by McCall, Newman, O'Brien, Valberg & Witts (1962) prompted a closer study of the preparation and constituents of this diet. 2. It became apparent that there was a discrepancy between the amounts of fat-soluble vitamins in the dietary formulation reported and the supposed final content of the diet. A diet prepared as described by McCall et al. (1962) contains 1000 mug (40 000 i.u.) ergocalciferol and 10 mug (14 500 i.u.) retinyl palmitate/kg. 3. An experiment was designed to study the effect of Fe-deficient and Fe-supplemented, high-vitamin-D diets, and an Fe-supplemented, normal-vitamin-D diet, on thyroid C cell volume and serum calcium concentration. 4. Thyroid C cell volumes and serum Ca concentrations were significantly higher in both groups given excess vitamin D than in the group given the Fe-supplemented, normal-vitamin-D diet. It is evident therefore, that hypervitaminosis D was the cause of the morphological and biochemical changes found in rats given the McCall et al. (1962) diet.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
customersupport@researchsolutions.com
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.