Relationship between luteal function and metabolic clearance and production rates of progesterone in the mare.

The research investigates the relationship between luteal function and the production and clearance rates of progesterone in horses. It looks at how the corpus luteum (CL), a structure that develops after ovulation and releases progesterone, performs according to the quantity of ovulations in a cycle.

Corpus Luteum Performance

The study examined the functional activity of the equine CL, specifically:

• The activity was measured by the CL’s ability to convert one type of hormone to another, specifically from [4-14C]3beta-hydroxy-5-en-20-one to [4-14C]pregn-4-en-3,20-dione.
• The study observed that the functionality of different age CLs lined up with the timeline of plasma progestagen concentrations – hormones involved in the menstrual cycle and pregnancy.

Multiple Ovulations

The researchers then studied mares that ovulated twice within the same cycle:

• It was found that the capacity for hormone conversion of the CL from the second ovulation was similar to that from the first ovulation.
• Once age adjustments were made, the CL from the first ovulation had a similar capacity to convert hormones as that resulting from a single ovulation in other mares.

Progesterone Production and Clearance

This research also touched on the clearance and production rates of progesterone:

• These rates were found to be similar in mares that ovulated once and those that had two ovulations.
• This proves that the number of ovulations in a cycle does not impact progesterone production or clearance rates.
• Further, the mares that ovulated once or twice exhibited a two-component disappearance curve, which looks at the rate of decrease of a certain substance, post the infusion of [3H]progesterone.