Evaluation of the combined glucose‐insulin and intravenous glucose tolerance tests for insulin dysregulation diagnosis in donkeys

Abstract

Article type : Original Article EVJ-GA-21-009.R2 Evaluation of the combined glucose-insulin and intravenous glucose tolerance tests for insulin dysregulation diagnosis in donkeys

Characterisation of the oral glucose and sugar tolerance tests and the enteroinsular axis response in healthy adult donkeys

“…Fasting baseline glucose and insulin concentrations were used to calculate the following proxies: glucose:insulin ratio, insulin:glucose ratio, modified insulin to glucose ratio, reciprocal of the square root of insulin, quantitative insulin-sensitivity check index, homeostasis model assessment for insulin resistant and homeostasis model assessment of percentage β-cell function. 7,28 The following parameters were obtained from the curves of each dynamic test: positive phase duration (time from the start to the time glucose returned to baseline), positive glucose clearance rate (ratio between the difference the highest measured and baseline glucose by the difference in time from the highest measured glucose to the end of the positive phase), negative phase duration (time from the end of positive phase to glucose returned to baseline); start-to-nadir interval (time from the start to lowest measured glucose), nadir concentration, valley duration (when applicable), negative glucose clearance rate (ratio between the difference the baseline glucose and the glucose nadir by the difference in time from the end of the positive phase and the lowest glucose), valley to baseline interval (time from minimal glucose until glucose returned to baseline), and area under the curve (trapezoidal method). 10,29,30…”

“…The prevalence of endocrine and metabolic disturbances, including hyperlipaemia, donkey metabolic syndrome (DMS) and pituitary pars intermedia dysfunction is increasing in donkeys, [4][5][6][7] thus there is a need to develop donkey-specific diagnostics. Guidelines for the diagnosis of equine metabolic syndrome (EMS) were recently updated, 8 with resting glucose and insulin concentrations together with overt clinical signs being the first screening for the diagnosis of EMS, although both having low diagnostic sensitivity, and dynamic testing being the hallmark for further diagnostic confirmation of insulin dysregulation (ID).…”

“…Guidelines for the diagnosis of equine metabolic syndrome (EMS) were recently updated, 8 with resting glucose and insulin concentrations together with overt clinical signs being the first screening for the diagnosis of EMS, although both having low diagnostic sensitivity, and dynamic testing being the hallmark for further diagnostic confirmation of insulin dysregulation (ID). 8 Numerous endocrine and metabolic differences between donkeys and horses have been reported, [5][6][7][9][10][11] but guidelines to diagnose ID in donkeys have not been generated.…”

“…The frequently sampled intravenous glucose-insulin tolerance test, the combined glucose-insulin test, the intravenous glucose tolerance test and the intravenous insulin tolerance test have been evaluated in healthy donkeys. 7,10,12,13 The enteroinsular axis comprises enteroendocrine factors (incretins) and insulin and plays a central role in postprandial glucose disposal and insulin response in horses, ponies and foals. 14,15 The best described incretins are glucose-dependent insulinotropic polypeptide (GIP) secreted by K cells in the proximal small intestine and glucagonlike peptide-1 (GLP-1) produced by L cells in the distal small intestine and proximal large intestine.…”

“…The revised EMS diagnosis guidelines recommend the oral sugar tolerance test (OSTT) in horses with ID 8 ; however, neither the OSTT nor the oral glucose tolerance test (OGTT) have been characterised in donkeys. The frequently sampled intravenous glucose‐insulin tolerance test, the combined glucose‐insulin test, the intravenous glucose tolerance test and the intravenous insulin tolerance test have been evaluated in healthy donkeys 7,10,12,13 …”