Experimental induction of C cell tumours in thyroid by increased dietary content of vitamin D3

Abstract

Abstract. Neonatal Wistar rats were given either 0, 5 or 10 μCi 131I 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.