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Abstract. Neonatal Wistar rats were given either 0, 5 or 10 μCi 131 I within 24 h of birth. Following weaning, they were fed a diet high, normal or deficient in vitamin D, for up to 2 years. Animals were sacrificed at approximately 3 monthly intervals, and serial sections of thyroid scanned for C cell tumours following calcitonin localization. Plasma calcium levels were also measured, and all results statistically analyzed. As expected, those animals given the high vitamin D had significantly raised calcium levels over those on a normal D diet, whilst those given a low D diet had lower calcium levels than normal. Analysis of the incidence of C cell tumours showed that those given a high D diet had significantly more C cell tumours, whilst those on a low D diet had significantly fewer than normal. Radiation dose also influenced C cell tumour incidence. There was a significant relationship between the vitamin D content of the diet and the incidence of C cell tumours, with those animals on a high D diet having the largest number of tumours. It is suggested that vitamin D or its metabolites may directly promote C cell growth, and that the high incidence of C cell tumours in the normal laboratory rat reflects the artificially high vitamin D content of the laboratory rat diet. The dietary vitamin D content may also be relevant to the variation in geographical incidence of medullary carcinoma in man. We consider it likely that vitamin D metabolites may play a significant role in the control of C cell function, hyperplasia and tumour formation in the rat, and that this may be more important in tumour formation than the role of serum calcium variation.
Thurston et al. (Sat,) studied this question.