Glucocorticoids and CBG during pregnancy in mammals: diversity, pattern, and function

Area of Science:

• Reproductive biology
• Endocrinology
• Comparative physiology

Background:

• Pregnancy involves complex hormonal changes, particularly glucocorticoids (GCs) and their binding protein, corticosteroid-binding globulin (CBG).
• Understanding GC-CBG dynamics during pregnancy is crucial for fetal development, yet data is limited to a few species like sheep, rodents, and humans.
• Generalizing findings from limited species to all placental mammals may be inaccurate.

Purpose of the Study:

• To investigate the diversity of maternal glucocorticoid and CBG patterns across placental mammal pregnancy.
• To determine if the observed GC-CBG dynamics in model species are representative of the broader mammalian class.

Main Methods:

• Compiled data on maternal GCs from blood samples of 13 species across 5 mammalian orders.
• Analyzed GC metabolites in excreta from an additional 20 species across 9 mammalian orders.
• Compared GC and CBG patterns throughout pregnancy in diverse placental mammals.

Main Results:

• Maternal free GCs generally increase in late pregnancy across most mammalian taxa studied.
• This increase is achieved through elevated GC secretion or reduced CBG levels.
• Even-toed ungulates (e.g., sheep, cows) show stable maternal GCs and CBG, with fetal adrenal maturation being key in late pregnancy.

Conclusions:

• Patterns of maternal GCs and CBG during pregnancy are species-specific.
• These diverse patterns represent alternative strategies to ensure increased fetal GC exposure, essential for development.
• Fetal adrenal maturation plays a significant role in species where maternal GC-CBG levels remain stable.