5α-dihydroprogesterone concentrations and synthesis in non-pregnant mares.

The research article focuses on the discovery that the hormone, 5α-dihydroprogesterone (DHP), is significantly present and synthesized in non-pregnant, ovulating horses. Findings also suggest that DHP may be synthesized outside the placenta, making horses potential models for studying reproductive hormonal behavior in other exotic species.

Research Methodology

• The study involved daily drawing of jugular blood from ovulating horses.
• Further, horses which had their ovaries removed (OVX) and geldings were administered with a dose of progesterone and had blood drawn before and after, to study the synthesis and ratio of DHP to progesterone.
• To investigate evidence of DHP synthesis, the research team conducted incubations of a horse’s whole blood and hepatic microsomes with progesterone.
• Sample analysis was completed employing a validated method of liquid chromatography-tandem mass spectrometry to ensure accurate results.

Findings

• In ovulating horses, progesterone and DHP were detected one day after ovulation, significantly increasing by the 3rd day, peaking at days 5-10, and decreasing from the 13th to 17th day.
• DHP was 55.5 ± 3.2% of progesterone concentrations throughout the cycle and showed a high correlation with it.
• Administering progesterone to OVX horses and geldings led to an immediate detection of DHP. The relative ratio was maintained between DHP and progesterone (47.2 ± 2.9 and 51.2 ± 2.7%, respectively).
• However, DHP was barely detectable in the whole blood and hepatic microsome incubations.

Conclusion

• The article concludes that DHP is a physiologically relevant progestogen in non-pregnant, ovulating horses, likely stimulating the uterus.
• It identifies that DHP is synthesized peripherally from luteal progesterone and not in the liver or blood.
• The presence of DHP in pregnant mammalian species suggests horses could be a valuable model for studying reproductive endocrinology in other exotic species.