Basal glucose metabolism and peripheral insulin sensitivity in equine pituitary pars intermedia dysfunction

Background: Glucocorticoids are suggested to precipitate laminitis and induce insulin resistance in horses. Hypothesis/Objectives: To assess insulin sensitivity and the basal amount of glucose metabolized in equine pituitary pars intermedia dysfunction (PPID). Animals and methods: The euglycaemic hyperinsulinaemic clamp (EHC) technique was performed in seven horses with a diagnosis of PPID based on the presence of hypertrichosis and positive dexamethasone suppression-test results comprising one gelding and six mares with a mean age of 21.1 +/- 5.8 (SD; range 15-34) years. Results were compared with those from five negative (healthy) controls comprising two geldings and two mares with a mean age of 10.0 +/- 2.5 (range 7-13) years and six positive (diseased) controls comprising two geldings and four mares with a mean age of 12.5 +/- 4.5 (range 8-21) years examined during the same period. Differences were assessed by means of the Mann-Whitney U test. Results: Mean basal rate of glucose metabolism (9.0 +/- 4.2 versus 16.0 +/- 5.2 micromol/kg BW/min; p = 0.030) and mean glucose metabolism rate-to-plasma insulin concentration ratio (2.9 +/- 1.6 versus 6.2 +/- 2.7 x 10(-6); p = 0.048) were significantly lower in PPID horses than in negative controls, respectively. No differences were found between both control groups. Conclusions and clinical importance: In horses suffering from PPID it seems important to reduce the insulin resistance, thereby potentially decreasing the risk of laminitis as being a major complication of equine PPID. Plasma glucose concentration following fasting might be considered in the screening of horses for PPID.