Pituitary pars intermedia dysfunction does not necessarily impair insulin sensitivity in old horses

Area of Science:

• Veterinary Medicine
• Equine Endocrinology
• Metabolic Diseases

Background:

• Equine Pituitary Pars Intermedia Dysfunction (PPID) is common in aged horses and has been linked to reduced insulin sensitivity.
• However, direct comparisons of insulin sensitivity between aged horses with PPID and age-matched controls are limited.

Purpose of the Study:

• To investigate insulin sensitivity and insulin-mediated signaling pathways in skeletal muscle of aged horses with PPID compared to healthy aged horses.
• To determine if PPID is associated with impaired glucose regulation and muscle metabolic alterations.

Main Methods:

• Isoglycemic hyperinsulinemic clamp procedures were performed on 12 aged horses (6 with PPID, 6 controls).
• Blood samples were analyzed for glucose, insulin, and amino acid concentrations.
• Skeletal muscle biopsies were collected to assess protein synthesis and breakdown signaling pathways.

Main Results:

• Insulin sensitivity, measured by glucose infusion rate during clamp, was similar between horses with PPID and controls.
• Plasma concentrations of indispensable amino acids decreased during insulin stimulation in both groups.
• PPID status did not affect the activation of protein synthesis/breakdown factors, though insulin stimulation increased phosphorylation of protein synthesis factors.

Conclusions:

• Aged horses with PPID do not necessarily exhibit reduced insulin sensitivity or altered skeletal muscle signaling pathways compared to healthy aged horses.
• The findings suggest that PPID may not be a primary driver of insulin resistance in all aged equine cases.