Specific PGF-2 alpha binding by the corpus luteum of the pregnant and non-pregnant mare.

This study examined how a type of prostaglandin (PGF-2 alpha) binds to luteal cells (cells found in the corpus luteum) of pregnant and non-pregnant Pony mares. Findings showed that the binding occurs in two different modalities depending on the affinity and capacity of the receptor, and the process is influenced by the stage of pregnancy.

Prostaglandin Binding Examination

Researchers conducted an in-depth study of the way prostaglandin F-2 alpha ([3H]PGF) binds to corpora lutea (CL), a structure that develops in the ovaries:

• The corpus luteum from both pregnant and non-pregnant Pony mares was analyzed.
• The binding was found to be specific and reversible.
• The binding process was examined through the rates of association and dissociation.
• [3H]PGF was bound specifically to a luteal cell membrane preparation (MP) isolated using high-speed ultracentrifugation.

Impact of Other Prostaglandins and Metabolites

• Different prostaglandins and prostaglandin metabolites were found to displace [3H]PGF from receptors.
• The order of displacement was: PGF-2 alpha > 13,14-dihydro-PGF-2 alpha = 13,14-dihydro-15-keto PGF-2 alpha > PGD-2 > PGF-1 alpha = PGE-2 > PGE-2 beta > PGE-1.
• This indicates the crucial role played by 9 alpha-OH and 5,6 cis double bond in PGF receptor recognition.

Observations on Receptor Populations

• The membrane preparation was found to contain at least two different receptor populations: high affinity, low capacity and low affinity, high capacity.
• These differences in affinity and capacity could influence how effectively PGF-2 alpha can bind to the luteal cells.

Prostaglandin Binding during Pregnancy

• The binding of PGF increased from Day 4 after ovulation to Day 12 and dropped afterward in non-pregnant mares.
• In pregnant mares, the binding of PGF continued to increase until Day 18 before it started to decline.
• The decrease in PGF binding by Day 16 in the non-pregnant mare might be indicative of the process of luteolysis – the degradation of the corpus luteum.
• High PGF binding capacity of CL between Days 16 and 18 of pregnancy suggests that maintaining the corpus luteum during pregnancy is not associated with a reduction of PGF binding capabilities.