Lecturer Veterinary Biosciences Melbourne Veterinary School, The University of Melbourne Werribee, Victoria, Australia
Abstract:
Background: Muscle atrophy is increasingly recognised as an important component of pituitary pars intermedia dysfunction (PPID), contributing to loss of use and activity, but the causes are poorly understood.
Objectives: To determine circulating factors associated with muscle atrophy, that may help identify the underlying mechanism(s). Animals: Thirty-five horses and ponies >15 years old; 13 with PPID and 22 without PPID.
Methods: Muscle atrophy and body condition were assessed using validated scoring systems. Plasma IGF-1, myostatin, activin-A and a panel of cytokines were measured using single-plex and multiplex ELISAs. Plasma metabolomics analysis was performed using gas chromatography-mass spectrometry.
Results: Body condition and cresty neck scores were similar in the PPID and non-PPID groups; however, muscle atrophy scores differed significantly (4-16 scale; median, PPID: 7 and non-PPID: 4; p=0.003). Plasma IGF-1, myostatin or activin A concentrations did not correlate with muscle atrophy and there were no differences between groups. However, myostatin showed a moderate correlation with body condition score (p=0.04). In the metabolomic analysis, only L-arginine showed a statistically significant difference, being lower in animals with muscle atrophy (p=0.026), Cytokines and chemokines detectable in plasma were not correlated with muscle atrophy or different between groups. Conclusions and clinical importance: The specific muscle atrophy scoring system is valuable for evaluating muscle atrophy in PPID cases. Muscle atrophy does not appear to be associated with pro-inflammatory cytokines or circulating levels of IGF-1, myostatin, activin A or with specific differences in metabolic pathways.
