Impact of blue light therapy on plasma adrenocorticotropic hormone (ACTH) and hypertrichosis in horses with pituitary pars intermedia dysfunction.

The study focuses on how blue light therapy affects the growth of winter hair coat and ACTH hormone levels in horses with pituitary pars intermedia dysfunction (PPID). Main findings indicate that blue light therapy doesn’t affect ACTH concentrations but reduces hair weight growth in PPID horses.

Background

• The research was provoked by the observation that horses with pituitary pars intermedia dysfunction (PPID) have an exaggerated increase in the secretion of the hormone adrenocorticotropic (ACTH) during the fall season.
• PPID horses frequently present with hypertrichosis, a condition of excessive hair growth.
• A hypothesis was proposed that blue light therapy could be used in horses to manipulate the natural photoperiod (day/night cycle), thereby inhibiting winter hair growth and managing hypertrichosis. Furthermore, its effect on ACTH was to be investigated.

Methodology

• Eighteen PPID horses were selected and divided into two groups based on their age and clinical history- a control group (10 horses) and a blue light therapy group (8 horses).
• The control group was exposed to natural photoperiod while the treatment group experienced consistent daylength of approximately 14.5 hours via wearable masks providing short wavelength blue light to one eye. This was done from mid-July to late October.
• To ascertain the PPID status of the horses, thyrotropin-releasing hormone (TRH) stimulation tests were performed. Plasma ACTH levels before and after TRH administration showed no differences between the two groups.
• To evaluate the effect of the therapy on ACTH, blood was collected for ACTH measurement at sequential timepoints over a 16-hour period in mid-October.
• Hair weights were also assessed during this period.

Findings

• The study found no significant difference in resting plasma ACTH levels between the two groups across the seasonal analysis (in July and October) or during the 16-hour testing period.
• However, horses with PPID given blue light therapy had lighter hair weights than the control group.

Conclusion

• Blue light therapy, while not altering ACTH concentrations, was found to potentially be a beneficial management tool for hypertrichosis in PPID horses by assisting in reducing the hair weight.
• The manipulation of photoperiod using blue light therapy had no significant impact on seasonal ACTH changes in this study.