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Development of thyroid function between VI-IX month of fetal life in humans
Insights
Fetal thyroid development shows significant variation in iodine utilization for hormone production, even with adequate iodine availability. This highlights a critical step in hormonogenesis during late gestation.
Area of Science:
- Endocrinology
- Developmental Biology
- Perinatal Medicine
Background:
- Thyroid hormone synthesis is crucial for fetal development.
- Understanding fetal thyroid function in late gestation is vital for assessing neonatal health.
- Iodine availability and utilization are key factors in thyroid hormone production.
Purpose of the Study:
- To investigate thyroid development and function in fetuses during late intrauterine life.
- To analyze iodine content, thyroglobulin (Tg) iodination, and hormone production in fetal thyroid glands.
- To compare thyroid parameters between preterm and term newborns.
Main Methods:
- Examination of thyroid glands from 28 fetuses (22-34 weeks) and 4 term newborns.
- Assay of total iodine, thyroglobulin (Tg), T4, T3, and rT3 before and after pronase hydrolysis.
- Measurement of cord-serum iodine and maternal/newborn urine iodine levels.
Main Results:
- Significant variations in thyroid iodine content and Tg iodination were observed among fetuses.
- Fetal thyroid glands demonstrated high Tg iodination, indicating enhanced iodine uptake.
- Hormonogenesis was active in the third trimester, comparable to mature thyroids, with preferential T4 and rT3 production.
Conclusions:
- Fetal thyroid iodine utilization for hormone production varies significantly, even with similar iodine availability.
- The primary limitation in some preterm infants was iodine utilization in hormone synthesis, not iodine or Tg levels.
- Thyroid development in late gestation involves complex regulation of iodine incorporation and hormone production.
Abstract:
Well-preserved thyroid glands from 28 fetuses 22-34 weeks of gestational age and from 4 term newborns who survived at most 12 days were examined to study thyroid development in late intrauterine life. Total iodine thyroglobulin (Tg), T4, T3 and rT3 were assayed before and after hydrolysis with pronase. In the same maternity unit the cord-serum of 25 healthy term newborns was also assayed and the urine iodine on the day of delivery was tested in 52 newborns and their mothers. Results are expressed as mean values +/- SD. The thyroid gland weight ratio to body weight for the preterms was 0.063 +/- 0.024; thyroid Tg content 5.9 +/- 4.0 mg/g; total thyroid iodine 41.7 +/- 35.1 micrograms/g; Tg iodination 0.72 +/- 0.37%; hormone quota of Tg iodine 39.9 +/- 12.4. Molar ratios were: T4/Tg 3.3 +/- 1.6, T3/Tg 0.25 +/- 0.14, rT3/Tg 0.072 +/- 0.059. Considerable differences in thyroid iodine content and Tg iodination were observed although the availability of iodine was presumably the same. The high Tg iodination reflects the enhanced uptake of the fetal thyroid. The quantity of iodine involved in hormonogenesis varied greatly among fetuses of the same gestational age, this being in the third term as active as in fully mature thyroids. Hormonogenesis seemed preferentially directed to production of T4 and rT3, which, in the latter case, is higher peripherically. Four preterms with a particularly low level of hormonogenesis were not seen to have deficient levels of thyroid iodine or Tg iodination and the most compromised step was the iodine utilization in the production of hormones.(ABSTRACT TRUNCATED AT 250 WORDS)