Concentration increase of unbound testosterone in plasma of the mare throughout pregnancy.

This research study investigates the changes in blood testosterone levels during the pregnancy of a mare (female horse). They discovered that testosterone levels rise at the beginning of pregnancy, peaking around the seventh month, before returning to basal levels after giving birth. It appears this testosterone increase is likely due to enhanced steroid production rather than changes in blood-specific binding activity, as seen in pregnant humans or guinea pigs.

Methodology and Key Findings

• The researchers used both Radioimmunoassay (RIA) and Gas Chromatography-Mass Spectrometry for measuring the blood testosterone levels in the pregnant mare. These are highly advanced techniques designed to enhance the accuracy of measurement.
• Throughout the pregnancy, they observed that testosterone levels increase from the very start, with the highest levels (about 10 times the baseline values) occurring at around the seventh month of gestation.
• In contrast to humans and guinea pigs, where increased blood testosterone in pregnancy results from an increase in blood-specific binding activity, the surge in the mare’s testosterone levels does not arise from the same cause.
• Both equilibrium dialysis and gel equilibration methods, which are used to explore blood-specific testosterone binding activity, did not show any alterations at any gestational stage in mares, suggesting a different mechanism at play here.

Suggested Reason for Increased Testosterone

• Based on the results, the scientists suggest that the observed testosterone increase probably occurs due to an increase in steroid production.
• The precise source of the testosterone increase may vary throughout the pregnancy period. They proposed that the mare’s gonads (ovaries) could be the source of the boost in early pregnancy. This would likely coincide with the production of Pregnant Mare Serum Gonadotropin (PMSG), a hormone that mares produce after fertilization and which is associated with the maintenance of pregnancy.
• Subsequently, the fetoplacental unit – the combined fetal and placental tissues – might be responsible for the further increase in testosterone.

Overall, this research provides new insights into the physiological changes that occur in mares during pregnancy, particularly regarding testosterone levels and potential causes of their fluctuation.