Concentration decrease of corticosteroid binding globulin (CBG) in plasma of the mare throughout pregnancy.

This study reports a significant reduction in the binding capacity of corticosteroid binding globulin (CBG) in the blood plasma of mares during pregnancy. This observed fall is related to an actual decrease in CBG concentration in the blood, which is a unique occurrence as compared to most other mammals, except for the pregnant rhesus monkey.

Research Objective

The objective of this research was to investigate the changes in the concentration and binding capacity of CBG during pregnancy in mares and compare this to what is known about CBG regulation in other mammalian species during gestation.

• Corticosteroid binding globulin (CBG) plays a critical role in regulating the physiological actions of cortisol and other glucocorticoids in the body. It helps in the transport and distribution of these hormones.
• Changes in CBG concentration can influence the amount of free, biologically active cortisol in the body, thus potentially impacting physiological responses such as immune function, metabolism, and stress responses.

Methodology

To demonstrate the decrease in CBG capacity in the mare’s plasma throughout pregnancy, the researchers used equilibrium dialysis and gel equilibration.

• Equilibrium dialysis is a technique used to measure the binding of a substance to a protein. In this case, it was used to assess the binding capability of CBG in mare’s plasma.
• Gel equilibration, like equilibrium dialysis, also measures protein interaction, but with a slightly different approach.
• The immunoelectrophoresis experiments were employed to understand whether the fall in CBG binding capacity was due to a decrease in blood CBG concentration. Immunoelectrophoresis is a method used to separate and characterize proteins based on their electrophoretic mobility.

Findings

The research revealed a significant decrease in CBG binding capacity in mares throughout their pregnancy.

• Comparisons were made to most other mammalian species, highlighting that in most species, CBG concentration increases during pregnancy, in stark contrast to the results of this study.
• This decrease is thought to be actual in nature, substantiated by the decreased concentration of the CBG in the blood.
• The reduced CBG concentration has potential bearings on the transportation and distribution of cortisol and other glucocorticoids in the pregnant mares, and potentially also on the regulation of physiological responses.
• This finding was found to be common with another mammalian species, the pregnant rhesus monkey, which is known to also exhibit a decrease in CBG levels throughout gestation.