Lamellar energy metabolism and perfusion in the euglycaemic hyperinsulinaemic clamp model of equine laminitis

Abstract

Background Hyperinsulinaemia is associated with the development of endocrinopathic laminitis; however, the mechanisms remain unclear. Objectives Evaluate the effects of hyperinsulinaemia on lamellar energy metabolism and perfusion during laminitis development. Study design In vivo experiment. Methods Eight Standardbred horses were instrumented with a microdialysis probe in the lamellae of a forelimb. A 24 hours baseline period (BASELINE) was followed by 48 hours of a continuous euglycaemic hyperinsulinaemic clamp (EHC) from 24 to 72 hours (CLAMP). Microdialysate was collected every 6 hours and analysed for glucose, lactate and pyruvate concentrations and lactate‐to‐pyruvate ratio (L:P). Microdialysis urea clearance was used to estimate lamellar tissue perfusion. Archived microdialysis samples from six identically instrumented Standardbred horses served as controls (CON). Variables were compared over time and between EHC and CON horses using a mixed‐effects linear regression model. Results Glucose concentration decreased during the CLAMP period in CON and EHC horses (P < .001), but there was no difference between CON and EHC (P > .9). Lactate concentration increased during the CLAMP period in CON and EHC horses (P < .001), however, the rate of increase was significantly higher in EHC horses relative to CON (P = .014). There was a relative increase in pyruvate concentration in EHC horses compared with CON during the CLAMP period (P = .03). L:P increased significantly in CON horses during the CLAMP period (P < .001) but not in EHC (P = .1). Urea clearance did not change in CON (P = .9) or EHC (P = .05) during the CLAMP, but did increase in EHC relative to CON (P = .02). Main limitations The effects of microdialysis probe implantation on perfusion and metabolism remain unclear. The EHC model may not mimic natural endocrinopathic laminitis. Conclusions Laminitis developed without evidence of lamellar hypoperfusion or energy stress. Therapies to improve perfusion are unlikely to affect the initial development of endocrinopathic laminitis.

Lamellar perfusion and energy metabolism in a preferential weight bearing model

“…Placement of the shoe insert to induce preferential weight bearing is denoted by ^ [Colour figure can be viewed at wileyonlinelibrary.com] (CON). Although not identified as a key process in the development of endocrinopathic or sepsis-related laminitis, 14,16 results of the current study support a likely role for ischaemia in the development of supporting limb laminitis.…”

“…The adjacent sublamellar dermis within the same (PWB) feet appeared unaffected, and these changes did not occur in the absence of altered limb load under otherwise identical conditions (CON). Although not identified as a key process in the development of endocrinopathic or sepsis‐related laminitis, 14,16 results of the current study support a likely role for ischaemia in the development of supporting limb laminitis.…”

“…The lactate:pyruvate [L:P] was calculated as a marker of tissue redox status. Urea clearance was calculated using the following equation, as previously described 16 :…”

“…Recently, a novel, nonpainful model utilising a platform shoe insert was successfully used to induce preferential weight bearing (PWB) for 48 hours, causing lamellar signalling changes (increased expression of hypoxia-inducible factor-1 alpha) suggestive of ischaemia. 11 By combining this model with tissue microdialysis, a technique that can detect temporal changes in lamellar perfusion and metabolism, [12][13][14][15][16][17] the objective of the current study was to investigate the effects of PWB on lamellar perfusion and energy balance.…”

Presence of Myeloperoxidase in Lamellar Tissue of Horses Induced by an Euglycemic Hyperinsulinemic Clamp

“…This study highlights the presence of MPO in equine lamellae of horses with insulin-induced laminitis, suggesting that neutrophil activation is also present in this model. All histologic sections of the treated horses presented well-described histological features of the hyperinsulinemia model such as elongated, narrowed secondary epidermal lamellae with tapered tips and acute-angle orientation, as well as rounded and centrally located nuclei ( 19 , 21 , 24 , 25 ). Together with the clinical signs of laminitis observed, this confirms that laminitis induction was successful.…”