title: Effect of a single dose of dexamethasone on glucose homeostasis in healthy horses by using the combined intravenous glucose and insulin test.
abstract: Sustained dexamethasone administration to horses results in insulin resistance, which may predispose them to laminitis. A single dose of dexamethasone is commonly used as a diagnostic aid, yet the effect of a single dose of dexamethasone on glucose homeostasis in horses is not well defined. The objective of this study was to characterize the change in glucose dynamics over time in response to a single dose of dexamethasone. A combined glucose-insulin tolerance test (CGIT) was performed on 6 adult geldings before and at 2, 24, and 72 h postdexamethasone (40 microg/kg of BW, i.v.); a minimum of 1 wk of rest was allowed between treatments. Before any treatment, the CGIT resulted in a hyperglycemic phase followed by a hypoglycemic phase. Dexamethasone affected glucose dynamics in 3 ways: 1) at 2 h, dexamethasone shortened the ascending branch of the negative phase (P < 0.001) of the test, indicating moderate insulin resistance; 2) at 24 h, dexamethasone impaired glucose clearance by extending the positive phase and eliminating the negative phase while insulin was elevated before the CGIT, indicating a decreased response to insulin; and 3) at 72 h, dexamethasone caused a deeper nadir value (P < 0.001) compared with predexamethasone, indicating an increased response to insulin. It was concluded that dexamethasone decreased the response to insulin as early as 2 h and maximally at 24 h. At 72 h, dexamethasone caused an increased response to insulin, which was unexpected.
authors.affiliation: Department of Agribusiness and Agriscience, Horse Science Center, Middle Tennessee State University, Murfreesboro 37129, USA. jhaffner@mtsu.edu
authors.forename: J C
authors.initials: JC
authors.lastname: Haffner
authors.forename: H
authors.initials: H
authors.lastname: Eiler
authors.forename: R M
authors.initials: RM
authors.lastname: Hoffman
authors.forename: K A
authors.initials: KA
authors.lastname: Fecteau
authors.forename: J W
authors.initials: JW
authors.lastname: Oliver
mesh_terms: D000818:Animals; D001786:Blood Glucose / Q000032:analysis; D003907:Dexamethasone / Q000494:pharmacology*; D005938:Glucocorticoids / Q000494:pharmacology*; D005947:Glucose / Q000008:administration & dosage / Q000378:metabolism; D005951:Glucose Tolerance Test / Q000662:veterinary; D006706:Homeostasis / Q000187:drug effects*; D006736:Horses / Q000378:metabolism*; D006854:Hydrocortisone / Q000097:blood; D007262:Infusions, Intravenous / Q000662:veterinary; D007328:Insulin / Q000008:administration & dosage / Q000097:blood / Q000378:metabolism; D008297:Male; D013997:Time Factors
chemical_list: D001786:Blood Glucose; D005938:Glucocorticoids; D007328:Insulin; D003907:Dexamethasone; D005947:Glucose; D006854:Hydrocortisone