HCG binding to the testicular LH receptor is similar in fertile, subfertile, and infertile stallions.

The study investigates whether the binding activity of the Luteinizing hormone (LH) receptor is affected in subfertile and infertile stallions, concluding that endocrine dysfunction in less fertile stallions may not result from an LH receptor disorder but possibly from a postreceptor malfunction.

Objective of the Study

• The research aimed to evaluate whether the LH receptor binding activity, a potentially crucial factor in male fertility, is altered in subfertile and infertile stallions compared to fertile ones.

Methodology

• Six fertile, three subfertile, and three infertile stallions, aged between 11 and 23 years, were used in the study. They were classified based on their normal semen parameters and pregnancy rates. Blood samples were collected from them prior to castration, during the breeding season.
• These blood samples were later analyzed for concentrations of LH, follicle-stimulating hormone (FSH), estrogen conjugates (EC), estradiol (E2), testosterone (T), and inhibin (I) using radioimmunoassay (RIA).
• Testicular cell membranes from the stallions were prepared and then analyzed for LH binding activity using a radioreceptorassay (RRA). This involved the use of increasing amounts of I125 human chorionic gonadotropin (hCG), a hormone used in fertility studies.
• The receptor number (Rt) and affinity constants (Ka) were calculated using Scatchard analysis, a method used for analyzing and comparing the results of ligand-receptor binding experiments.

Key Findings

• The study found that the levels of LH, FSH, EC, E2, and T did not noticeably differ between fertile and subfertile stallions. However, LH and FSH levels were significantly higher in infertile stallions compared to fertile and subfertile ones, while EC, E2, T, and I levels were considerably lower.
• Importantly, the receptor number (Rt) and affinity constants (Ka) were found to be similar in all three categories of stallions (fertile, subfertile, and infertile).
• These results suggest that an endocrine dysfunction in the testes of subfertile and infertile stallions might not be caused by a LH receptor disorder, as previously suspected, but could be due to some postreceptor malfunction.

Conclusion

• This research provides important insights into the possible causes of reduced fertility in stallions. It points towards a potential malfunction at the postreceptor level, rather than any issues with the LH receptor itself. This could be a useful finding for further research into stallion infertility and potential treatments.