ABSTRACTMECHANISM OF INTESTINAL AND SKELETAL MUSCLE GLUCOSE AND AMINO ACID UPTAKE IN PITUITARY PARS INTERMEDIA DYSFUNCTIONByJennifer L. De VriesPituitary pars intermedia dysfunction (PPID) is characterized by a progressing loss of dopaminergic inhibition of the pituitary pars intermedia and commonly causes poor physical appearance, hirsutism, and muscle loss in the geriatric horse. We hypothesized that horses with PPID have reduced tolerance to glucose and sensitivity to insulin, reduced mRNA abundance of SLC2A4, INSR, and SLC38A2, and reduced protein expression of GLUT4 and INSR in muscle tissue, reduced intestinal morphology, and reduced D-glucose and L- Gln transport capacity across the jejunal mucosa, and mRNA abundance of SLC5A1 and SLC38A2 compared to horses with no PPID. Horses were maintained on hay and senior feed for a period of 5 d while being monitored for medical stability. Presence and grade of PPID was determined based on endocrine testing and post mortem histopathological evaluation of the pituitary gland. Intestinal and gluteal muscle samples were harvested and processed. The results of this study show that muscle wasting and poor physical appearance associated with the pathology of the PPID condition is not due to a reduced transporter abundance at the intestinal and systemic level, but may be due in part to a reduced intestinal morphology. Geriatric horses and those with PPID in particular should be carefully managed with feeding diets containing low concentration of soluble carbohydrates in an effort to decrease the risk of laminitis.
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