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The appearance and activity of tissue thyroxine 5'- and 5-monodeiodinase during ontogenesis in the fetal pig
A B Slebodziński1, E Brzezińska-Slebodzińska
1Department of Developmental and Experimental Endocrinology, Polish Academy of Sciences, Poznan.
Insights
This study investigated fetal piglet development of monodeiodinase enzymes, crucial for thyroid hormone regulation. Key findings reveal significant increases in liver 5-deiodinase activity near term, correlating with specific sulfhydryl groups.
Area of Science:
- Endocrinology
- Developmental Biology
- Biochemistry
Background:
- Fetal development of monodeiodinase systems is poorly understood, with limited data in species beyond rodents, rabbits, and chicks.
- Monodeiodinases are critical enzymes regulating thyroid hormone (TH) metabolism, converting thyroxine (T4) to active triiodothyronine (T3) or inactive reverse triiodothyronine (rT3).
Purpose of the Study:
- To characterize the ontogeny of 5'- and 5-monodeiodinase activities in fetal and neonatal pigs.
- To investigate the relationship between monodeiodinase activities, TH levels (T4, T3, rT3), and sulfhydryl groups (T-SH, NP-SH) during porcine gestation and early postnatal life.
Main Methods:
- Assessed 5'- and 5-monodeiodinase activities in liver, kidney, and placenta of pig fetuses (day 32 to birth) and neonates (days 1-14).
- Measured serum concentrations of T4, T3, and rT3, along with total and non-protein sulfhydryl groups.
- Utilized 123 fetuses, 32 neonates, 15 sows, and 10 non-pregnant pigs.
Main Results:
- 5'- and 5-monodeiodinase activities were detected in the placenta by day 32 of gestation and in the liver at the onset of thyroid hormone biosynthesis.
- Liver 5'-monodeiodinase activity remained low until approximately day 93, then increased sharply, peaking two days before term.
- Liver 5'-monodeiodinase activity exceeded that of maternal, newborn, and non-pregnant adult tissues; increased non-protein sulfhydryl groups in liver/kidney and total sulfhydryl groups in the placenta correlated with heightened 5'-monodeiodinase activity.
Conclusions:
- The placenta plays a role in early fetal deiodinase activity, while the liver's capacity significantly matures late in gestation.
- The observed increase in liver 5'-monodeiodinase activity near term is linked to changes in sulfhydryl group levels, suggesting a regulatory mechanism.
- This study provides novel insights into the developmental endocrinology of thyroid hormone metabolism in a large animal model.
Abstract:
The ontogeny of the fetal monodeiodinase systems, during the period before the onset of thyroid activity until birth, has been described only in the rat, rabbit and chick. We have studied 5'- and 5-monodeiodinase activities in the liver, kidney and placenta of pig fetuses, from day 32 of gestation up to birth, and on days 1, 3, 7 and 14 after birth. Fetuses (123) from 15 litters, 32 newborn piglets, 15 sows (mothers) and 10 non-pregnant pigs were used. The relationships between monodeiodinase activities, thyroxine (T4), tri-iodothyronine (T3) and reverse triiodothyronine (rT3) blood serum concentrations and sulphydryl groups (total (T-SH) and non-protein (NP-SH)), were measured. 5'-Monodeiodinase activity (5'-MD type I; converting T4 to T3) and 5-monodeiodinase (5-MD; converting T4 to rT3) were detectable in the liver at the onset of thyroid hormone biosynthesis, and before that time (day 32 of gestation) in the placenta. Liver 5'-MD activity was very low between days 32 and 84 of gestation, and then increased rapidly at about day 93, reaching a maximal value 2 days before term. Activity in the liver (but not in the kidney) was higher than that in maternal, newborn and non-pregnant adult tissue. The increase in NP-SH groups in the liver and kidney and T-SH groups in the placenta during the last 5 days of gestation coincided with the increase in 5'-MD activity.(ABSTRACT TRUNCATED AT 250 WORDS)