Associations among beta-endorphin, ACTH, cortisol concentration, age, and clinical signs indicative of pituitary pars intermedia dysfunction in geriatric horses.

Background Limited published data are available regarding the relationships among clinical signs associated with pituitary pars intermedia dysfunction (PPID), age, and concentrations of proopiomelanocortin-derived peptides and cortisol. Hypothesis/objectives Identify clinical signs associated with age, beta-endorphin (β-END), adrenocorticotropic hormone (ACTH), and cortisol concentrations and compare β-END and cortisol concentrations between horses with PPID and geriatric controls. Animals A total of 113 horses aged 18-32 years. Methods Cross-sectional study. Clinical signs were scored, plasma β-END, ACTH, and serum cortisol concentrations were measured, and their associations were evaluated. Horses were classified as PPID or controls based on haircoat abnormalities and ACTH concentrations, and group comparisons were performed. Results Increased β-END and ACTH concentrations were associated with haircoat abnormalities (P < .001), whereas advanced age was associated with muscle atrophy, weight loss, and lethargy (P < .001). Cortisol concentrations were not associated with any of the clinical signs. The β-END concentrations were higher in the PPID group (median, 291 pg/mL; interquartile range IQR, 122-836 pg/mL; n = 40) compared with the control group (median, 55.0 pg/mL; IQR, 45.0-68.0 pg/mL; n = 53; P < .001). Conclusions And Clinical Importance In this geriatric study cohort, haircoat abnormalities were associated with increased β-END and ACTH concentrations, whereas other clinical signs, such as muscle atrophy, weight loss, and lethargy, were primarily linked to age. Because PPID is diagnosed based on clinical signs and ACTH concentrations, it is important to distinguish clinical signs that are age-related from those associated with PPID.