Dietary iodine affects epidermal growth factor levels in mouse thyroid and submaxillary glands

To determine whether dietary iodine intake affects the levels of immunoreactive epidermal growth factor (EGF) in vivo in two mouse tissues known to be thyroid hormone responsive, 24 adult BALB/c mice were randomized into groups of six animals and fed a) an iodine-deficient diet, b) normal laboratory chow (controls), c) an iodine-deficient diet with high physiological iodine supplementation (approximately 300 micrograms/day), and d) an iodine-deficient diet with pharmacological doses of iodine (approximately 3 mg/day). After 21 days on the various regimens, the mice were killed and the concentration of mouse (m) EGF in the thyroid and submaxillary glands (SMG) measured by radioimmunoassay. The mean (+/- SEM) SMG mEGF level (micrograms/mg wet weight) in the different groups were: a) 7.58 +/- 1.87, b) 12.46 +/- 4.7, c) 19.79 +/- 4.47, and d) 24.36 +/- 5.96. The thyroid mEGF concentrations (ng/mg wet weight) were: a) 3.65 +/- 0.75, b) 5.23 +/- 1.84, c) 8.07 +/- 1.18, and d) 6.43 +/- 0.95, respectively. Analysis of variance revealed that dietary iodine status had a significant effect on mEGF levels in both the SMG (p < 0.001) and the thyroid gland (p < 0.001). Compared to controls, tissue mEGF levels decreased by 30-40% in the mice fed an iodine-deficient diet, and increased by 60-150% following physiologic iodine replacement.