EFFECTS OF MARGINAL IODINE DEFICIENCY ON THYROID-HORMONE PRODUCTION, DISTRIBUTION AND TRANSPORT IN NONPREGNANT AND NEAR-TERM PREGNANT RATS

During pregnancy maternal thyroid hormones are of great importance for normal development of the central nervous system of the fetus. Iodine deficiency of the mother can result in an impaired development of the fetal brain. In large areas of the world iodine intake is moderately low. To study the effects of marginal iodine deficiency (MID) on the p roduction, distribution, and transport of thyroxine (T-4) and 3,5,3'-t ri-iodothyronine (T-3) in nonpregnant and near-term pregnant rats we p erformed kinetic experiments (three-compartment analysis). Despite unc hanged plasma T-4 and T-3 during MID, the production and plasma cleara nce rates of T-4 decreased 30% (P = 0.01) in MID nonpregnant (MID-C) r ats. For T-3, the plasma clearance rate was increased 70% (P = 0.046), while the T-3 production was more than doubled (P = 0.042) in MID-C r ats. In MID near-term pregnant rats T-3 production was decreased 20% ( P = 0.04), Hepatic deiodinase type I activity increased during MID in both nonpregnant and pregnant rats. It appears that during MID, rats a re able to maintain their euthyroid status, The pronounced increase in transport of T-4 from plasma to the fast pool observed in pregnant ra ts on a normal iodine diet did not occur during MID, In conclusion in rats MID affects maternal thyroid hormone metabolism, thus influencing the availability of maternal T-4 for the fetus.