Effect of Dietary Nonstructural Carbohydrate Content on Activation of 5′-Adenosine Monophosphate-Activated Protein Kinase in Liver, Skeletal Muscle, and Digital Laminae of Lean and Obese Ponies

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Abstract

Background:

In EMS-associated laminitis, laminar failure may occur in response to energy failure related to insulin resistance (IR) or to the effect of hyperinsulinemia on laminar tissue. 5′-Adenosine-monophosphate-activated protein kinase (AMPK) is a marker of tissue energy deprivation, which may occur in IR.

Hypothesis/Objectives:

To characterize tissue AMPK regulation in ponies subjected to a dietary carbohydrate (CHO) challenge.

Animals:

Twenty-two mixed-breed ponies.

Methods:

Immunohistochemistry and immunoblotting for total AMPK and phospho(P)-AMPK and RT-qPCR for AMPK-responsive genes were performed on laminar, liver, and skeletal muscle samples collected after a 7-day feeding protocol in which ponies stratified on body condition score (BCS; obese or lean) were fed either a low-CHO diet (ESC + starch, approximately 7% DM; n = 5 obese, 5 lean) or a high-CHO diet (ESC + starch, approximately 42% DM; n = 6 obese, 6 lean).

Results:

5′-Adenosine-monophosphate-activated protein kinase was immunolocalized to laminar keratinocytes, dermal constituents, and hepatocytes. A high-CHO diet resulted in significantly decreased laminar [P-AMPK] in lean ponies (P = .03), but no changes in skeletal muscle (lean, P = .33; obese, P = .43) or liver (lean, P = .84; obese, P = .13) [P-AMPK]. An inverse correlation existed between [blood glucose] and laminar [P-AMPK] in obese ponies on a high-CHO diet.

Conclusions and Clinical Importance:

Laminar tissue exhibited a normal response to a high-CHO diet (decreased [P-AMPK]), whereas this response was not observed in liver and skeletal muscle in both lean (skeletal muscle, P = .33; liver, P = .84) and obese (skeletal muscle, P = .43; liver, P = .13) ponies.

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