Evaluation of a thyrotropin-releasing hormone solution stored at room temperature for pituitary pars intermedia dysfunction testing in horses.

This study aimed to establish if plasma ACTH levels in horses change when administered a thyrotropin-releasing hormone (TRH) solution prepared under different conditions. The research concluded that the TRH test shouldn’t be repeated within 24 hours, and a TRH solution stored at room temperature could be effectively used for the stimulation testing in horses.

Research Methodology

The research comprised of two separate but similar experiments, both focusing on evaluating the variation in plasma ACTH (Adrenocorticotropic hormone) concentrations in horses following the introduction of TRH solutions, prepared and stored differently. TRH is a hormone that aids in the release of the thyroid-stimulating hormone and prolactin.

• In the first experiment, thirty horses were divided into three groups. Each horse went through two TRH stimulation tests with a 24 hours gap. The difference was in the preparation and storage condition of the TRH solution. One group received a TRH solution prepared by a compounding pharmacy and stored at room temperature (cTRH), another prepared for research purposes and stored at -20°C (rTRH) while the third group got rTRH for both tests.
• In the second experiment, the researchers followed a design similar to the first experiment, but with a longer gap of 14 days between tests. They also altered the number of horses in each group.

Findings

• Some horses showed mild, transient effects such as temporary coughing and yawning, following the administration of the TRH solutions.
• In the first experiment, the median delta ACTH (change in ACTH concentration post-TRH administration) responses for the second test was significantly lower than that of the first test for all groups, suggesting the TRH stimulation test should not be repeated within 24 hours.
• In the second experiment, the median delta ACTH response did not display a significant difference between the first and second tests for any group, indicating that the 14 days gap between tests may have mitigated the difference observed in the first experiment.
• The research also noted a positive correlation (rs = 0.95) between ACTH concentrations after rTRH and cTRH administration, meaning the preparation and storage conditions of the TRH solutions had little impact on the outcomes.
• The mean ± SD bias (average difference between measures) in post-TRH ACTH concentration between rTRH and cTRH was 2.9 ± 12.4 pg/mL, which is not significant, leading to the conclusion that cTRH solution stored at room temperature could be effectively used for TRH stimulation testing in horses.