Circulating antagonist of luteinizing hormone in association with infertility in stallions.

The research investigated the association of a luteinizing hormone (LH) antagonist with infertility in stallions, finding that a substance in the blood may prevent LH from binding to its receptor, thereby inhibiting reproductive functions and contributing to infertility.

Methods and Findings

• To find this potentially reproductive-inhibiting substance, the researchers used a radioligand receptor assay (RRA) and a monoclonal radioimmunoassay (RIA) that are known to work in serum. This led them to identify a group of less fertile stallions that had a higher RRA to RIA ratio than usual.
• The scientists isolated the active part of the substance using anion exchange chromatography and immunoprecipitation with the equine luteinizing hormone (eLH) monoclonal antibody. Even after these purification steps, RRA activity remained, which suggests that the active part of the substance may be one that blocks the binding of the hormone to its receptor.
• The purified active fraction was recognized by a polyclonal LH antibody with broad cross-species recognition, indicating that the substance may interact with the LH receptor in a similar way across different species.
• This fraction was further purified and shown to block labeled eLH from binding to its receptor in a dose-dependent manner in the RRA. The fraction also inhibited LH-stimulated steroidogenesis – the production of steroids that is essential to the reproductive function – in Leydig cells in vitro in a dose-dependent manner.
• However, the substance doesn’t impact basal steroid production, which means it only affects steroidogenesis when LH is present.
• The researchers then ran polyacrylamide gel electrophoresis and electroelution, two techniques used to analyze proteins, on the substance. This revealed that the molecule had a weight ranging from 45-66 kDa, suggesting that it may be a protein or peptide.

Conclusion

• From their findings, the researchers concluded that this substance blocks the binding of eLH and human chorionic gonadotropin (hCG), another hormone important for reproduction, to the LH receptor.
• It also inhibits LH’s ability to stimulate steroidogenesis, which is crucial for reproductive processes.
• The substance may be a form of LH that is found in infertile stallions, suggesting a possible link between this substance and infertility in these animals.