Lamellar perfusion and energy metabolism in a preferential weight bearing model.

Abstract

BACKGROUND: Supporting limb laminitis (SLL) is suspected to be caused by lamellar ischaemia as a consequence of increased mechanical load. OBJECTIVES: Examine the effects of prolonged preferential weight bearing (PWB) on lamellar perfusion and metabolism. STUDY DESIGN: In vivo experiment. METHODS: Microdialysis probes were inserted in the lamellar and sublamellar dermis of one forelimb in 13 Standardbred horses. In six horses, a platform shoe (contralateral forelimb) was used to induce increased load on the microdialysis-instrumented forelimb (PWB). The remaining seven horses were controls (CON). All horses were housed in stocks with limb weight distribution logged continuously for 92&#xa0;hours. Microdialysate was collected and analysed every 4&#xa0;hours for glucose, lactate, pyruvate, and lactate to pyruvate ratio (L:P). Microdialysis urea clearance was used to estimate lamellar perfusion. Data were analysed using a mixed-effects linear regression model. RESULTS: Median [IQR] load on the microdialysis-instrumented limb was equivalent to 38.7%&#xa0;bwt. [37.3-40.3] in PWB and 27.3%&#xa0;bwt. [26.6-28] in CON. Limb offloading frequency increased in CON (P&#xa0;<&#xa0;.001) but not PWB (P&#xa0;=&#xa0;.2). Lamellar microdialysate glucose decreased in PWB (P&#xa0;<&#xa0;.001) and CON (P&#xa0;=&#xa0;.004), however, the rate of decrease was higher in PWB (P&#xa0;=&#xa0;.007). Lamellar L:P increased in PWB (P&#xa0;<&#xa0;.001) and peaked at 196 [79-656], whereas L:P did not change over time in CON (P&#xa0;=&#xa0;.6) and peaked at 42 [41-49]. Lamellar urea clearance decreased in PWB (P&#xa0;<&#xa0;.001) but not in CON (P&#xa0;=&#xa0;.3). Sublamellar L:P and urea clearance did not change over time in either group (P&#xa0;>&#xa0;.05). MAIN LIMITATIONS: The PWB model may not be representative of naturally occurring SLL. CONCLUSIONS: Evidence of lamellar ischaemia (increased L:P and decreased urea clearance) was detected exclusively in the lamellar dermis of PWB feet subjected to persistently increased load. Lamellar ischaemia is a consequence of increased mechanical load and likely contributes to the development of SLL.