Glucose-dependent insulinotropic polypeptide (GIP) and the enteroinsular axis in equines (Equus caballus)

To investigate the enteroinsular axis (EIA) in equines oral (oGTT) and intr avenous (i.v.GTT) glucose tolerance tests (5.6 and 1 mmol glucose/kg BW, re spectively) were performed with healthy, normal weight large horses and She tland ponies. Plasma was analysed for concentrations of glucose, glucose-de pendent insulinotropic polypeptide (GIP) and insulin. In all equines plasma GIP concentrations only increased significantly when glucose was administe red orally. The insulin glucose ratio (IGR) was significantly higher during the oCTT than during the i.v.GTT in both races. Basal plasma glucose level s were significantly higher in large horses than in ponies in both experime nts. During the oGTT maximum glucose values were significantly higher in po nies. Ponies tended to a higher insulin secretion but the IGRs were identic al in both races after oral and intravenous glucose administration. One cli nically inconspicuous pony showed hyperinsulinaemia and, in case of the oGT T, insulin resistance, glucose intolerance, and GIP hypersecretion. The res ults of this study indicate the existence of an EIA in equines due to the h igher IGRs during the oGTT. Furthermore, the similarity of plasma GIP level s and IGRs in ponies and large horses suggest a comparable activity of the EIA in both races. Regarding the elevated plasma GIP concentrations of the insulin resistant pony the EIA appears to participate in equine hyperinsuli naemia. (C) 2001 Elsevier Science Inc. All rights reserved.