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This Article Full Text (PDF) All Versions of this Article: jas.2008-1179v1 87/1/131    most recent Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Haffner, J. C. Articles by Oliver, J. W. Search for Related Content PubMed PubMed Citation Articles by Haffner, J. C. Articles by Oliver, J. W.

Effect of a single dose of dexamethasone on glucose homeostasis in healthy horses using the combined intravenous glucose and insulin test

J. C. Haffner^*, H. Eiler, R. M. Hoffman^*, K. A. Fecteau and J. W. Oliver

^* Department of Agribusiness and Agriscience, Horse Science Center, Middle Tennessee State University, Murfreesboro, TN 37129 Department of Comparative Medicine, College of Veterinary Medicine, The University of Tennessee, 2407 River Drive A205, Knoxville, TN 37996

jhaffner{at}mtsu.edu

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 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 post-dexamethasone (40 µg/kg 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 to pre-dexamethasone, 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 increased response to insulin which was unexpected.

Key Words: dexamethasone • glucose • horse • hyperglycemia • insulin