α-Melanocyte–stimulating hormone and adrenocorticotropin concentrations in response to thyrotropin-releasing hormone and comparison with adrenocorticotropin concentration after domperidone administration in healthy horses and horses with pituitary pars intermedia dysfunction.

The research compared the release of two hormones (ACTH and α-MSH) in response to the administration of the thyroid-releasing hormone (TRH) and the release of ACTH after the administration of domperidone in healthy horses and those suffering from pituitary pars intermedia dysfunction (PPID). The study found that measuring the ACTH levels in response to TRH was a more accurate way to diagnose PPID in horses than using domperidone.

Research Aim and Methodology

• The researchers aimed to compare the concentration of Adrenocorticotropic hormone (ACTH) and α-Melanocyte–stimulating hormone (α-MSH) released in reaction to the administration of thyrotropin-releasing hormone (TRH).
• They also wanted to compare the concentration of ACTH after administering TRH with that after administering domperidone in two sets of horses – healthy horses and those with pituitary pars intermedia dysfunction (PPID).
• For this study, they selected 69 normal horses and 47 horses with suspected or confirmed PPID.
• ACTH concentrations were measured in 88 horses during a total of 108 TRH stimulation tests, while α-MSH concentration was measured in 56 such tests conducted on 50 horses.
• In 28 horses, ACTH concentration was also measured following domperidone administration.

Findings and Conclusions

• In the research results, it was found that both ACTH and α-MSH concentrations saw an increase in all horses after TRH administration, but horses with PPID had a more substantial increase.
• The researchers noted that the percentage increase was higher for α-MSH concentration than ACTH.
• However, the change in ACTH concentration after domperidone administration was less indicative of the distinction between normal horses and those with PPID.
• In conclusion, the research suggests that testing the ACTH concentration after administering TRH is a more accurate marker for diagnosing PPID when compared to the response after domperidone administration.
• Essentially, an α-MSH concentration of ≥ 30 or 50 pmol/L was found to be not superior to an ACTH concentration of ≥ 36 pg/mL for diagnosing PPID in horses, either before or half an hour after TRH administration.