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An assessment was made of the influence of low-iodine diet on somatic and brain development at birth (day 0) and 21 days postnatally in the rat. The rat mothers were proven to be iodine-deficient by assay of plasma thyroxine and thyroid stimulating hormone prior to mating, and at 21 days postnatally, when maternal thyroids were removed, weighed and stored for subsequent iodine analysis, along with those of the offspring. There were no significant differences in body weight or brain weight of the offspring at birth, or in the content of DNA or protein. However, at 21 days there was a significant reduction in body weight (21 ·7%) and whole brain weight (7·9 %, P < 0·02) which was associated with a significant fall in cholesterol content (12·4 %, P < 0·05) and protein level (9·6%, P < 0·01), while DNA was not significantly affected (6%). The greatest reduction in weight was seen in the cerebellum. The thyroids in these rats were double normal size, showed follicular cell hypertrophy and absence of colloid histologically, and contained 8 % of the iodine content of controls.It is concluded that iodine deficiency retards both somatic and brain development, the change in the latter case being expressed as a reduction in cell size in the cerebral hemispheres and cerebellum, along with reduced myelination throughout the brain.

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