The effect of pergolide mesylate on adrenocorticotrophic hormone responses to exogenous thyrotropin releasing hormone in horses.

The study investigates how pergolide, a medication for pituitary pars intermedia dysfunction (PPID) in horses, impacts the effectiveness of repeat thyrotropin-releasing hormone (TRH) stimulation tests as a method of assessing treatment response. Results were analyzed from 64 horses suspected of having PPID before and after pergolide treatment. The findings reveal improvements in hormone response within 100 days of treatment, but not all horses’ test results normalized.

Research Context

• The research is centered on pituitary pars intermedia dysfunction (PPID) in horses. PPID is a common equine metabolic disorder characterized by abnormal functioning of the pituitary gland.
• One of the methods used to diagnosis PPID is the thyrotropin releasing hormone (TRH) stimulation test, which monitors the secretion of the adrenocorticotrophic hormone (ACTH) in response to TRH.
• However, the validity of performing repeated TRH stimulation tests after initiating PPID treatment is uncertain.

Research Methodology

• In this study, the researchers observed the effect of pergolide – a medication commonly prescribed for PPID – on TRH stimulation tests in 64 horses suspected of having the disorder.
• These horses were subjected to a TRH test before treatment and then a follow-up test within 100 days of initiating pergolide therapy. A subset of these horses also underwent additional follow-up tests beyond the 100-day mark.
• Tests conducted between a specific date range were excluded to avoid potential seasonal influences.

Key Findings

• Significant improvements in ACTH concentrations were observed within 100 days of starting pergolide treatment. These improvements were evident in baseline ACTH concentrations as well as TRH-stimulated ACTH concentrations.
• Upon post-treatment TRH stimulation test, a substantial 88% (56 out of 64) of cases showed a decreased response to TRH.
• However, of the horses with positive pre-treatment TRH stimulation test outcomes, only 24% (9 out of 38) normalized following pergolide treatment. An additional 34% (13 out of 38) improved to an equivocal test outcome category.
• Interestingly, most horses (42% or 16 out of 38) with a pre-treatment positive TRH stimulation test continued to test positive after treatment, albeit a smaller numerical response in 75% of these cases was seen.

Relevance and Implications of the Research

• The results indicate that while pergolide treatment for PPID brings about significant hormonal improvements within a 100-day period, not all horses’ TRH stimulation test results normalized.
• This could be useful information for veterinary practitioners, helping manage treatment expectations for horse owners and allowing for more informed decisions when interpreting changes in TRH stimulation test outcomes in horses receiving pergolide therapy for PPID.