妊娠時の甲状腺機能と絨毛性サイロトロピン (hCT) の意義に関する研究
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概要
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A study of the contributions of human pituitary thyrotropin and human chorionic thyrotropin to normal thyroid homeostasis during pregnancy.<BR>With the use of a recently developed, sensitive and specific radioimmunoassay for hCT and hTSH, the author examined the serum concentrations of hCT and hTSH in 220 normal pregnant women from the 2nd month of pregnancy through parturition, and compared the levels with the concentrations of other polypeptide hormones obtained from the same serum sample. To assess the effect of TRH on the secretion of hCT and hTSH, TRH was administrated in a dose of 100pg to 60 pregnant women in the first to the 3rd trimester of gestation. Simultaneously, thyroid function was evaluated with various routine examinations.<BR>Serum hCT was detectable even at the end of the 2nd gestational month (3.3μg/ml ± 1.4 S.E.), tending to increase gradually toward the 3rd trimester (28.0μg/ml±24.6 S.E. at the term). Baseline hTSH values did not change during pregnancy and there were no significant differences in the baseline values in normal non-pregnant (2.7μU/ml ± 1.6 S.E.) and pregnant women (3.9μU/ml ± 2.6 S.E.). Serum hTSH levels increased in all subjects during each trimester after TRH administration. The mean values for ΔhTSH were 13.9μU/ml ± 2.2 S.E. in the first, 14.5μU/ml± 1.9 S.E. in the second and 13.0μU/ml ± 1.5 S.E. in the third trimester. The hTSH response to TRH remained unaltered as compared with non-pregnant women. Serum hCT levels showed no significant change after TRH. Serum T3, T4 concentrations and values of PBI or TBG-binding capacity were demonstrated to rise gradually during pregnancy in a manner similar to serum hCT levels. The mean values for Triosorb decreased gradually and the values of ETR remained within the non-pregnant range throughout pregnancy. And there existed positive correlations not between hTSH and T3, T4 concentrations but between hCT and T3, T4 concentrations in individual samples.<BR>In summary, in non-pregnant women thyroid function is controlled by pituitary hTSH (hypothalamic-pituitary-thyroid axis). In pregnant women, it is possible to say that thyroid function is controlled slightly by hTSH, but is never enhanced by hTSH. Thyroid function in pregnant women is enhanced by hCT itself which has a higher activity in serum than that of hTSH. Meanwhile, TBG-binding capacity is known to be increased by estrogen. Then, estrogen increased during pregnancy makes TBG bind with more thyroid hormones and keeps free thyroxine in the non-pregnant range. TBG neither elevated the serum hTSH level nor altered thyroid function progressively toward the 3rd trimester of pregnancy.<BR>As mentioned above, it may be possible to say that the thyroidal homeostasis during pregnancy is mainly controlled by "placento-thyroidal axis".
- 日本内分泌学会の論文