Plasma Insulin-Like Growth Factor-1 Concentration in Horses with Equine Pituitary Pars Intermedia Dysfunction
Department of Physiological Sciences, Oklahoma State University Center Veterinary Health Sciences
Stillwater, OK, USA
Insulin-like growth factor (IGF-1) is a pluripotent hormone with a role in growth, metabolism, and cell survival. IGF-1 has been shown to protect neurons from toxic and inflammatory-induced damage and IGF-1 deficiency has been reported to occur with neurodegenerative disease. Equine pituitary pars intermedia dysfunction (PPID) is a neuroendocrine disease that results from dopaminergic neurodegeneration. We hypothesized deficiency in IGF-1 contributes to development of PPID. The aim of this study was to determine the plasma IGF-1 concentration in equids with PPID.
Plasma was collected from animals with or without clinical evidence of PPID. Disease status was confirmed by plasma α-MSH concentration or postmortem examination. IGF-1 was determined by immunoradioassay, insulin-like growth factor binding protein-3 (IGFBP-3) by ELISA. Relative IGF-1 was calculated [IGF-1 (nmol/L)/IGFBP-3 (nmol/L)]. Mean results from animals with PPID were compared to controls by t-test.
Plasma IGF-1 and IGFBP-3 concentration was greater in normal ponies compared to normal horses (IGF-1: 437±140 ng/ml, n=25 versus 249±105 ng/ml, n=30, P<0.001; IGFBP-3: 794±292 ng/ml, n=25 versus 419±317 ng/ml, n=30, P<0.0001). Plasma IGF-1 concentration in horses with PPID was significantly greater than in healthy horses (442±210 ng/ml, n=25 versus 249±105, n=30 ng/ml, P<0.01). While relative IGF-1 was greater in horses with PPID, it failed to reach significance (P = 0.08). Plasma IGFBP-3 concentration was similar in healthy and PPID horses. There was no difference in any IGF-related measurement in ponies with PPID compared to healthy ponies. These unexpected findings warrant further investigation to determine the role of IGF-1 in horses with PPID.