Thyroid hormones in tissues from human embryos and fetuses

Area of Science:

• Endocrinology
• Developmental Biology
• Human Physiology

Background:

• Thyroid hormones are crucial for fetal development.
• Fetal thyroid function matures later in gestation.
• The role of thyroid hormones before functional maturation is not fully understood.

Purpose of the Study:

• To quantify triiodothyronine (T3) and thyroxine (T4) in human embryonic, fetal, neonatal, and adult tissues.
• To evaluate the role of thyroid hormones in fetal development prior to fetal thyroid maturation.
• To understand thyroid hormone influence in adult tissues.

Main Methods:

• Measurement of T3 and T4 using Gordon and coworkers' method.
• Analysis of embryonic (6-12 weeks gestation), fetal/neonatal (15-36 weeks gestation), and adult human tissues.
• Tissues analyzed included limbs, carcasses, brain, liver, heart, kidney, lung, skeletal muscle, and skin.

Main Results:

• T3 and T4 were detected in embryonic limbs (9-12 weeks) at concentrations significantly lower than maternal blood.
• T3 and T4 levels increased substantially in embryonic carcasses from 9-12 weeks gestation.
• Hormone concentrations increased with gestational age in fetuses and adults, with T4 predominant in serum.

Conclusions:

• T3 and T4 are present in early human embryos before the fetal thyroid becomes functional, likely originating from maternal circulation.
• Detected hormone levels, though low, raise questions about their potential role in early fetal development.
• Thyroid hormone levels and distribution change significantly from embryonic stages through adulthood.