Journal of animal science2010; 88(9); 2940-2949; doi: 10.2527/jas.2010-2879

Hyperleptinemia in mares and geldings: assessment of insulin sensitivity from glucose responses to insulin injection.

Caltabilota, TJ
·
Earl, LR
·
Thompson, DL
·
Clavier, SE
·
Mitcham, PB

Abstract: Four experiments were conducted 1) to assess the use of glucose responses to insulin injections as a means of estimating insulin sensitivity in horses and 2) to compare the insulin sensitivities of normal horses vs. those displaying hyperleptinemia (HL). In Exp. 1, HL mares and geldings (n = 4 each) and 4 mares and geldings with normal leptin concentrations (NL) were injected intravenously with 20 and 100 mU/kg of BW of bovine insulin on 2 separate occasions in December 2008. In Exp. 2, the experimental protocol was repeated in late April 2009. In Exp. 1, the 20 mU/kg of BW dose of insulin caused a greater (P < 0.05) decline in glucose concentrations in NL mares and geldings compared with HL horses. The response of HL mares to the 100 mU/kg of BW dose was less (P 0.1), whereas the greater dose revealed differences (P 0.1) for LL mares, regardless of BCS, and was less (P < 0.01) than for mares with increased leptin concentrations. It was concluded that a dose of 50 mU/kg of BW of recombinant human insulin could be used safely to start the dose-response curve; smaller or larger doses could then be applied as appropriate to get sufficient data for estimation of ED50. Experiment 4, conducted in October of 2009, assessed the repeatability of the estimates for ED50 obtained in Exp. 3. Six mares with LL vs. increased leptin concentrations received the 50 mU/kg dose of insulin; appropriate larger or smaller doses were used to obtain estimates of ED50. Estimates obtained were highly correlated (r = 0.91) with those obtained in Exp. 3, with an average within-mare CV of 8.9%; this is equal to or better than the repetabilities of the currently used methods of assessing insulin sensitivity in horses. It was concluded that hyperleptinemic horses, which are also hyperinsulinemic and have exaggerated insulin responses to glucose injection, are indeed less sensitive to insulin than normal horses with reduced leptin concentrations of the same body condition.

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Publication Date: 2010-05-21 PubMed ID: 20495126DOI: 10.2527/jas.2010-2879Google Scholar: Lookup

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The researchers conducted four experiments to determine if glucose responses to insulin injections can be used to measure insulin sensitivity in horses and compared these measurements between normal horses and horses with high leptin levels (hyperleptinemia). The results showed that horses with high leptin levels, which also had high insulin levels and over-the-top insulin responses to glucose injections, were less sensitive to insulin than normal horses with lower leptin levels.

Study Overview

The investigation involved four experiments designed to assess the utility of glucose responses to insulin injections for evaluating insulin sensitivity in horses. The researchers also sought to compare insulin sensitivity between horses with normal leptin levels and those with hyperleptinemia.
Hyperleptinemia in horses, characterized by high concentrations of leptin hormone, is often associated with high insulin levels and exaggerated insulin responses to glucose injections. Insulin sensitivity relates to how effectively the body’s cells respond to insulin to take in glucose for energy.

Key Experimental Procedures and Findings

In experiments 1 and 2, hyperleptinemic mares and geldings, as well as their normal leptin level counterparts, were intravenously injected with bovine insulin at two different concentrations. Researchers monitored the ensuing glucose level changes. In experiment 1, insulin caused a greater decline in glucose levels in normal leptin horses compared to hyperleptinemic ones.
The third experiment focused on examining the insulin dose-response relationship in mares with different insulin sensitivities. To this end, researchers used varying doses of human insulin. Subsequently, the dose causing a 50% decline in glucose levels (ED50) was estimated. The ED50 was significantly less for horses with increased leptin levels compared to those with lower levels.
The last experiment assessed the repeatability of the ED50 estimates obtained in experiment 3. The estimates were found to be highly correlated, providing evidence of the repeatability of the methodology.

Conclusions

Hyperleptinemic horses, characterized by high insulin levels and exaggerated insulin responses to glucose injections, proved to be less sensitive to insulin than normal horses with reduced leptin levels of the same body condition.
The response to insulin injection, measured via changes in glucose levels, can serve as an effective method for assessing insulin sensitivity in horses.
These findings have potential implications for the management of insulin-related conditions in horses, and possibly, for therapeutic strategies involving insulin sensitivity alteration.

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APA

Caltabilota TJ, Earl LR, Thompson DL, Clavier SE, Mitcham PB. (2010). Hyperleptinemia in mares and geldings: assessment of insulin sensitivity from glucose responses to insulin injection. J Anim Sci, 88(9), 2940-2949. https://doi.org/10.2527/jas.2010-2879