Prolonged effect of a single injection of human chorionic gonadotrophin on plasma testosterone and oestrone sulphate concentrations in mature stallions.

This study looks at how a single injection of human chorionic gonadotrophin (hCG) affects testosterone and oestrone sulphate levels in mature stallions over time.

Research Context and Aims

• The study aims to investigate the prolonged effects of a single dosage of human chorionic gonadotrophin (hCG) on testosterone and oestrone sulphate plasma levels in mature stallions.
• Particular interest was given to how the introduced hCG, typically used to induce ovulation in female animals, would affect the concentration of these sex hormones.

Study Methodology

• In the experiment, two pony stallions were injected with 6,000 international units (iu) of hCG.
• Peripheral plasma samples were regularly taken from the animals under study and analyzed for changes in testosterone and oestrone sulphate concentrations.

Results and Findings

• According to the results, testosterone levels in both stallions notably increased and remained elevated for five days after the hCG injection.
• This intense increase in testosterone concentration demonstrated no adverse effects on hormone levels later on in the experiment.
• Regarding oestrone sulphate, there was an initial spike in one pony after the hCG injection, after which the concentrations dropped to below pre-injection levels. Despite having a higher initial concentration of oestrone sulphate, the second stallion did not show the same increase after the injection but did record a significant decrease from the fifth day after treatment.

Study Implications and Remaining Questions

• The study indicates that a single hCG injection has prolonged hormonal effects in stallions, particularly on testosterone and oestrone sulphate levels, which were observed for several days after the injection.
• Even though some horses showed different responses, notably in oestrone sulphate concentrations, the overall trend suggests a suppression in oestrone sulphate levels. It is however currently unclear whether this suppression is directly attributable to the high testosterone levels caused by the hCG injection. Further research is needed to fully understand the relationship between these hormonal changes.