Whole-body phenylalanine kinetics and skeletal muscle protein signaling in horses with pituitary pars intermedia dysfunction.

The research investigates the impact of pituitary pars intermedia dysfunction (PPID) on the behavior of phenylalanine (an essential amino acid) in horse bodies and how it relates to muscle protein synthesis and breakdown. The study found no significant differences between horses with and without PPID in terms of phenylalanine kinetics and the activation of signaling pathways that control muscle protein synthesis and breakdown.

Objective of the Research

• The research aimed to investigate the effect of pituitary pars intermedia dysfunction (PPID), a common endocrine disorder in aging horses, on both phenylalanine metabolism and muscle protein synthesis and breakdown in the body of horses.

Research Methodology

• The study involved 12 aged horses split into two groups: one group composed of 6 horses suffering from PPID, and a control group also composed of 6 horses that didn’t have PPID.
• Plasma glucose, insulin, and amino acids concentrations were determined before and after feeding.
• Gluteal muscle biopsy samples were collected 90 minutes after feeding and subjected to tests that determined abundance and activation of factors involved in muscle protein synthesis and breakdown.
• All horses were given a priming dose and a constant rate infusion of (13)C sodium bicarbonate followed by a priming dose and a constant rate infusion of 1-(13)C phenylalanine IV to determine whole-body protein synthesis.

Key Findings

• There was a postprandial increase in plasma glucose and insulin concentrations in both groups of horses. However, there was no significant postprandial increase in plasma amino acids concentrations detected in either group.
• Phenylalanine flux, oxidation, release from protein breakdown, and nonoxidative disposal were not significantly different between groups.
• No significant effect of PPID status was detected on the quantity or activation of positive or negative regulators of protein synthesis or positive regulators of protein breakdown.

Conclusions

• The study concludes that in aged horses, PPID seems to have no significant impact on whole-body phenylalanine kinetics or the postprandial activation of signaling pathways that regulate protein synthesis and breakdown in muscles.