Pergolide and Muscle Atrophy in PPID Horses

While pergolide improves the health of many horses with pituitary pars intermedia disorder (PPID, Cushing’s disease), it may not slow muscle atrophy, a classic sign of the disease, according to a recent study.

“Increased breakdown of muscle protein and decreased protein synthesis may contribute to muscle wasting, but the exact mechanisms specifically involved in PPID-affected horses are not clear,” explained Kathleen Crandell, Ph.D., a nutritionist for Kentucky Equine Research. About half of all horses diagnosed with PPID have some degree of muscle atrophy.¹

“One published study suggested that pergolide can decrease muscle atrophy in up to 46% of horses within six months of initiating therapy. That study used a subjective ‘muscle-wasting score’ but not a control group, leaving the role of pergolide in muscle atrophy relatively undefined,” Crandell explained.²

Researchers recently investigated the physiology of muscle atrophy in horses with and without PPID as well as in PPID horses that were treated with pergolide or a placebo. All of the horses in the study were at least 15 years old with a body condition score of 6 or higher. The researchers measured markers of muscle atrophy, adiposity, insulin regulation, skeletal muscle composition, and proteolysis in all horses after 12 weeks of treatment.³ Proteolysis is the breakdown of proteins or peptides into amino acids by enzymatic action.

Researchers found that horses with PPID had more muscle atrophy than those without PPID. This was established by comparing the diameter of the longissimus dorsi, the largest muscle in the horse’s body that lies along the spinal column and contours the topline. While pergolide did not improve muscle atrophy or reduce markers of protein breakdown, it enhanced insulin regulation and promoted weight loss. In contrast, untreated PPID horses experienced weight gain and increased rump-fat thickness.

The inability of pergolide to slow muscle atrophy might reflect the short testing period. Twelve weeks of pergolide therapy may not have been enough to elicit an improvement in muscle mass or muscle breakdown in PPID horses. Further research in this area is warranted.

“Horses with PPID struggling with muscle atrophy may benefit from a well-balanced diet with plenty of protein, such as a high-quality ration balancer. Many ration balancers contain the necessary nutrients, including protein, to build muscle,” Crandell recommended.

¹Ireland, J.L., and C.M. McGowan. 2018. Epidemiology of pituitary pars intermedia dysfunction: A systematic literature review of clinical presentation, disease prevalence, and risk factors. Veterinary Journal 235:22-33.

²Corrected freedom of information summary: Prascend tablets, pergolide mesylate, horse. https://animaldrugsatfda.fda.gov/adafda/app/search/public/document/downloadFoi/890. Accessed June 3, 2021.

³Banse, H.E., A.E. Whitehead, D. McFarlane, and P.K. Chelikani. 2021. Markers of muscle atrophy and impact of treatment with pergolide in horses with pituitary pars intermedia dysfunction and muscle atrophy. Domestic Animal Endocrinology 76:106620.