Vitamin A repletion in rats with concurrent vitamin A and iodine deficiency

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http://www.ncbi.nlm.nih.gov/pubmed/17311942?ordinalpos=16 & itool=EntrezSystem2.PE\

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Vitamin A repletion in rats with concurrent vitamin A and iodine

deficiency affects pituitary TSHbeta gene expression and reduces

thyroid hyperstimulation and thyroid size.

Biebinger R, Arnold M, Langhans W, Hurrell RF, Zimmermann MB.

Human Nutrition Laboratory, Institute of Food Science and Nutrition,

ETH Zurich, Switzerland. ralf.biebinger@...

Concurrent vitamin A (VA) deficiency (VAD) and iodine deficiency (ID)

are common in developing countries. VAD has effects on thyroid

metabolism that may be dependent on iodine status. The aim of this

study was to investigate the effect of VA supplementation (VAS) and/or

dietary iodine repletion, alone and in combination, on the

thyroid-pituitary axis in rats with concurrent VAD and ID. Weanling

rats (n = 96) were fed diets deficient in VA and iodine or sufficient

in both (control), for 30 d. Subsequently, deficient rats were

repleted with iodine and/or single VAS or remained deficient for 10 d.

Serum retinol (SR), thyroid hormones, serum thyrotropin (TSH),

pituitary TSHbeta mRNA expression level, and thyroid weight were

measured. High-dose VAS restored SR concentrations to normal in both

iodine-deficient and iodine-sufficient rats. Despite continuing VAD,

provision of the iodine-sufficient diet entirely reversed the

abnormalities of the pituitary-thyroid axis produced by VAD and ID. In

iodine-sufficient rats, VAS had no discernible effects on the

pituitary-thyroid axis; in iodine-deficient rats, VAS reduced

pituitary production of TSH and thyroid stimulation but had no

discernible effects on circulating thyroid hormone concentrations.

Primary hypothyroidism in rats with concurrent VAD and ID does not

reduce the efficacy of VAS, nor does VAD reduce the efficacy of

dietary iodine to correct pituitary-thyroid axis dysfunction due to

ID. In concurrent VAD and ID, VAS, independent of iodine repletion,

reduces thyroid hyperstimulation and size, an effect likely mediated

through the effects of VA on pituitary TSHbeta gene expression.