EFFECTS OF PREGNANCY ON IODINE METABOLISM IN THE PRIMATE*†

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Abstract
In contrast to the human, the rhesus macaque exhibits rapid thyroidal accumulation of I131 which is not augmented by pregnancy. The effects of pregnancy on several parameters of iodine metabolism in the macaque are similar to the effects observed during estrogen therapy in nonpregnant humans. These are: an increase in thyroxine binding by the thyroxine -binding globulin, slowing of the fractional rate of thyroxine turnover, and an increase in the concentration of circulating hormone without an appreciable change in the volume of distribution of thyroxine. Accordingly, the net daily hormonal turnover is no different during pregnancy than in the nonpregnant animal. A similar phenomenon was noted in 2 of 3 women similarly studied during and after therapeutic abortions. In the first woman there was an appreciable slowing of the fractional rate of thyroxine turnover during pregnancy, with a return to normal values after abortion. In the 2 other women, who suffered significant intercurrent illnesses, the rates were characteristic of normal nonpregnant subjects. In 1 of these 2 women, the rate was further accelerated during the postpartum follow-up period. Consequently, the net quantity of hormone turned over daily was the same during pregnancy as it was post partum. However, in the other woman the net hormonal turnover was markedly reduced at the time of postpartum follow-up examination. At the time of abortion, the concentration of organic I131 in fetal serum was approximately one-fifth that in maternal serum.