Plasma adrenocorticotropic hormone concentration in horses decreases after freezing for 60 days.

The research conducted a study on the stability of adrenocorticotropic hormone (ACTH) in horse plasma under different freezing conditions for varying durations. The findings revealed that freezing plasma samples at -20°C and -80°C resulted in ACTH degradation after 60 and 90 days respectively, whereas no such degradation occurred when the samples were stored betwixt ice packs for 7 days, or frozen at -20°C for 30 days or at -80°C for 60 days.

Study Design and Methodology

• This research examined the stability of ACTH, a pituitary hormone that regulates the stress response in animals, in horse plasma, under different freezing conditions and for varying periods.
• The plasma samples of 12 horses were taken and ACTH concentrations were measured at day 0 (baseline) and subsequently over time, after stimulation with thyrotropin-releasing hormone — a hormone that triggers the release of thyroid hormones from the thyroid gland.

Experimental Process

• The samples were stored at different conditions: -80°C for 3, 7, 30, 60, and 90 days; -20°C for 3, 7, 30, and 60 days; and between ice packs at -20°C for 3 and 7 days.
• The concentration of ACTH was then determined for these samples that had been stored under different conditions for varying time.
• For comparative analysis, ACTH concentrations in these samples were compared to the baseline (non-frozen day 0 plasma) for each storage method.

Data Analysis and Results

• A mixed model with repeated measures was applied to analyze the data. In this model, each horse served as its own control and the repeated effect was the day.
• Statistical significance was defined as (p-value) ≤ 0.05, while a p-value between 0.05 and 0.10 represented a trend.
• The analysis revealed that storage of plasma ACTH frozen at -20°C or -80°C led to ACTH degradation when compared to baseline samples after 60 and 90 days respectively.
• No ACTH degradation was observed after 7 days when samples were tucked between ice packs, or before 30 days at -20°C, or before 60 days at -80°C.

Conclusions

• The findings in this study illustrate the significant impact that the duration and conditions of storage have on the structural integrity of ACTH in horse plasma under freezing conditions.
• This information is integral for ensuring accurate measurements of ACTH concentration over time, particularly when these plasma samples are stored for extended periods.