Table 3 General summary about the developmental thyroid hormone mechanisms (deiodinases, transporters, sulfotransferases and receptors) in human, rat and chicken [16]
Human | Rodent (rat) | Chicken | |||
|---|---|---|---|---|---|
Week post conception | Day post conception | Incubation day | |||
1 W | - D3 is detected in uterine wall. | 1 GD | D2 and D3 are observed in uterine wall. | 5 h (blastula stage) | - TRα mRNA is noticed and the levels markedly increased during neurulation. |
3 W | - Thyroid gland begins. | 7 -8.5 GD | - Time of implantation process. | 24 h | - mRNA levels of D1, D2, and D3 are detected in whole embryos. |
- Very high D3 activity is detected in decidual tissue. | |||||
4-6 W | - TBG is observed in thyroid follicle cells at GD 29. | 9 GD | - Thyroid gland is first visible as an endodermal thickening in the primitive buccal cavity. | 48 h | - OATP1C1 expression appears. |
- TRH is detected in fetal whole-brain at 4.5 weeks of gestation. | Â | - TH is detected in rat embryotrophoblasts | |||
- T4 is transferred via the placenta and has been found in the gestational fluid sac from 4 to 6 W. | |||||
5-11 W | - Maternal-embryo transfer of THs has been detected in embryonic coelomic fluid and amniotic fluid. | ||||
- All the mRNAs encoding THTs are expressed in placenta from 6 W and throughout pregnancy. | |||||
8 W | - T4, T3 and rT3 are detected in coelomic/amniotic fluids. | 10 GD | - T4, T3 and TRβ are detected in embryo/trophoblast unit. | E2-E4 | - T3, THTs, Ds and TRs are expressed in whole embryos. |
- TRs, D2 and D3 are noticed in fetal brain. | |||||
10 W | - TSH is first detected in the fetal pituitary. | E4 | - OATP1C1 expression is more than 10-fold higher in the telencephalon and diencephalon compared to the mesencephalon and rhombencephalon. | ||
- D2 mRNA levels are highest in the diencephalon. | |||||
8-10 W | - The fetus is able to produce THs during this period, but prior to that time, is totally dependent on maternal THs. | E5 | - TRα mRNA is widely distributed in fore-, mid- and hind-brain. | ||
11 W | - TBG levels are detected in fetal serum and increased through gestation. | E6 | - T4 and T3 are detected in embryonic brain. | ||
8-11 W | - TRH is detected in fetal hypothalamus. | E7 | - D2 activity is observed in the brain before the onset of thyroid function and increases significantly. | ||
12 W | - T4 and T3 are observed in serum and brain. | 13 GD | - Placental circulation established. | E8 | - D2 mRNA is noticed in cell clusters throughout the brain, particularly in rhombencephalon. |
- Total serum T4 and T3 are low, free T4 is relatively high. | Â | - TRs and TH are observed in fetal brain. | Â | - OATP1C1 levels are declined substantially in all brain regions. | |
- rT3 is noticed in serum relatively high. | Â | - D3 and D2 are detected in uterus and placenta. | |||
- TH synthesis begins in fetal thyroid. | |||||
- Decreased mRNA expression of OATP1A2 but no change for OATP4A1 at 9–12 W compared to term. | |||||
14 W | - Expressions of mRNAs encoding MCT8, MCT10, OATP1A2 and | 14 GD | - TRH mRNA is detected in neurons of the fetal hypothalamus. | E4-E8 | - D3 mRNA levels are markedly different in the telencephalon and diencephalon but remain stable, while the levels in mesencephalon and rhombencephalon show a sharp decrease and increase, respectively, during these days. |
LAT1 are significantly lower prior to 14 W compared to term | |||||
15 GD | - Pituitary TSH mRNA expression begins. | E9-10 | - Several elements of the TH action cascade are observed in the brain of embryos long before their own thyroid gland starts hormone secretion. | ||
- TRH mRNA is detected in the developing paraventricular nuclei of the hypothalamus. | |||||
16 W | - D3 is observed in placenta and fetal epithelial cells. | 16-19.5 GD | - TRs are observed in liver, heart and lung. | E10 | - The thyroid gland is fully functional. |
- D3 and TRs are detected in fetal liver. | Â | - D1 and D2 are noticed in fetal tissues. | |||
- D1 is noticed in heart and lung. | Â | - TRH is produced in low levels in hypothalamus and increases approximately threefold by GDI9.5. | |||
- Significant fetal TH secretion begins. | |||||
16-20 W | - Duplication of TBG concentrations. | 17 GD | - TH synthesis begins in fetal thyroid | E13 | - Brain D2 is elevated at the peak of neuroblast proliferation. |
- TSH protein and Sulfotransferase are observed. | |||||
18 -22 GD | - The total T4 and T3 concentrations in fetuses are increased dramatically because of maturation of hormone synthesis of the fetal thyroid gland. | E14 | - The strong increase in intracellular T3 has been observed. | ||
- The coordination between THTs and Ds is regulated both transplacental TH passage from mother to fetus and the development of the placenta itself through the progress of gestation. | |||||
20 W | - A steady increase in serum TH levels begins and continues to term. | 19 GD | - Significant fetal TH secretion begins. | E15 | - Plasma T4 levels start rising markedly around this day. |
- Marked rise in serum TH but levels at birth still below those in adult. | |||||
22-32 W | - Serum total and free T4 and T3 near and below adult levels, respectively. | 22 GD | - Birth state. | E16 | - The decrease in DI activity in gonads is combined with the relatively high D3 activity. |
- Thyroid system is less developed. | |||||
- The HPT axis begins to mature during the second half of gestation. | Â | - As much as 17.5% of THs found in the newborn are of maternal origin. | Â | - A significant increase in T3 production and in D2-activity and -mRNA expression are combined with a decreased in D3 activity. | |
- LAT1 and OATP4A1 have been localized only during the third trimester. | |||||
40 W | - Birth state. | 10 PND | - Brain development equivalent to human birth. | E13/14–E17 (synaptogenesis) | - Brain D2 activity is moderately elevated, whereas D3 activity and mRNA expression are highest between these days, followed by a dramatic decrease thereafter. |
- Complete maturation of thyroid system. | |||||
- MCT8 has been localized in the placenta in all three trimesters of pregnancy. | |||||
- High concentrations of the different iodothyronine sulfates, T4S, T3S, rT3S and T2S, have been documented in human fetal and neonatal plasma as well as in amniotic fluid during the pregnancy. | 10-20 PND | - Serum TH levels continue to rise and are higher than adult levels between these days. | E18 | - D1 and D3 are expressed in the granule cells, whereas D2 is found mostly in the molecular layer and the Purkinje cells at that time. | |
14-50 PND | - The levels of pituitary and serum TSH slowly decrease from PND 14–16 until reaching adult levels at PND 40. | E19 | - The increase in brain T3 production correlates with the appearance of TRβ expression in the cerebellum, telencephalon and optic lobes. | ||
- TRH levels increase to adult levels by PNDI7–29, then decrease transiently between PND 31–41; adult levels are once again reached at PND 50. | |||||
E20 (at the moment of pipping) | - The brain is quite well developed at the time of hatching. | ||||
- Adult TRH mRNA expression patterns are observed at PND 22. | Â | - The gradual increases in plasma T4 and hepatic D1 are detected. | |||
- D3 levels are decreased in spleen and increased in skin and the lungs towards hatching. | |||||
- T3 production seems to be elevated markedly in liver. | |||||
- The rise of T4 is much more pronounced than in plasma. | |||||
- Diminished T4 sulfation is detected. | |||||
30 PND | Complete maturation of thyroid gland. | E14-E19/20 | - The T3 breakdown capacity by D3 is high in liver but low in kidney. | ||
E15/16-E20 | - T4 levels in plasma increase gradually during these days. | ||||
- In contrast to TRα expression which increases gradually towards hatching, expression of TRβ shows an abrupt elevation in late development, especially in the cerebellum. | |||||
- The majority of tissues express D3 together with either D1 or D2. | |||||
E17-E20 | - The levels of D3 activity noticed in liver are rapidly drop by more than 90%. | ||||
- D1 levels in testis and ovary strongly decrease around hatching. | |||||
E18–E20 | - Brain D2 activity is moderately decreased, whereas D3 activity is low. | ||||
E19-E20 | - The low T3/T4 ratio is associated with high T3 breakdown in liver and with high T4 inactivation or T3 secretion in kidney. | ||||
E20-C0 | - D1 activity gradually increases, reaching a maximum around these period, and decreases slowly to posthatch levels thereafter. | ||||
C1 (first day posthatch) | - The expression of D1 is limited to the mature granule cells and that of D3 to the Purkinje cells exclusively, whereas D2 remains clearly noticed in the molecular layer. | ||||
C2 | - Highest D1-activities and -mRNA expressions are detected in the liver, kidney, and intestine. | ||||
C1-C7 | - The circulating T3/T4 ratio started to increase gradually during the first week after hatching. | ||||