Hypothyroidism prolongs corpus luteum function in the pregnant rat

Area of Science:

• Reproductive Endocrinology
• Thyroid Physiology
• Maternal-Fetal Medicine

Background:

• Hypothyroidism in rats is linked to prolonged gestation.
• This is associated with a delayed decrease in circulating progesterone (P4) levels at term.
• The underlying mechanisms of altered luteal function remain unclear.

Purpose of the Study:

• To investigate if delayed P4 decline in hypothyroid rats stems from reduced P4 degradation or increased synthesis.
• To explore the mechanisms behind altered luteal function in hypothyroid pregnancies.
• To identify hormonal and molecular factors contributing to prolonged gestation.

Main Methods:

• Radioimmunoassay (RIA) to measure circulating hormone profiles (TSH, PRL, LH, P4, PGF2alpha, PGE2).
• Quantitative Reverse Transcription Polymerase Chain Reaction (RT-PCR) to assess gene expression of factors in P4 synthesis and metabolism.
• Western blot analysis to quantify protein levels of key enzymes.

Main Results:

• Hypothyroidism resulted in delayed luteal regression and parturition.
• Key luteolytic factors (PGF2alpha, iNOS mRNA, LH) were decreased, while luteotrophic factors (PGE2, PRL) were increased.
• Expression of 20alphaHSD (involved in P4 degradation) was significantly reduced, leading to elevated P4 levels.

Conclusions:

• Prolonged pregnancy in hypothyroid rats is due to retarded luteal regression.
• This is caused by a combination of decreased luteolytic and increased luteotrophic signals.
• Reduced 20alphaHSD expression is a key factor in maintaining high progesterone levels, prolonging gestation.