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- Author or Editor: Janet C. Patterson-Kane x
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Abstract
Objective—To determine cellular changes associated with secondary epidermal laminae (SEL) in forefeet and hind feet of ponies with insulin-induced laminitis.
Animals—8 ponies.
Procedures—Laminitis was induced in 4 ponies by IV administration of insulin and glucose; 4 control ponies received saline (0.9% NaCl) solution IV. Laminar tissue samples obtained from the dorsal aspects of the hooves were histologically evaluated. Primary epidermal lamina (PEL) length and width and SEL length, width, and angle were determined. Numbers of epidermal cell nuclei per micrometer and per total length of SEL and numbers of apoptotic and proliferative cells in axial, middle, and abaxial laminar regions were determined.
Results—SEL in treatment group ponies were significantly longer, were significantly narrower, and had a smaller angle relative to PEL in all laminar regions versus control ponies. In treatment group ponies, the number of epidermal cell nuclei per SEL was typically higher and the number of cells per micrometer of SEL was lower in laminar regions, apoptotic cell numbers were higher in abaxial and middle regions in forefeet and hind feet, and proliferating cell numbers were higher in axial laminar regions in forefeet and all laminar regions in hind feet, versus control ponies.
Conclusions and Clinical Relevance—Results indicated SEL elongation, narrowing, and alteration in orientation developed in all feet of ponies with insulin-induced laminitis. This was primarily attributable to cell stretching that developed at the same time as an accelerated cell death–proliferation cycle; differences in cell cycle responses among laminar regions between forefeet and hind feet may have been attributable to differences in load bearing.
Abstract
Objective—To determine whether specific treadmill exercise regimens would accelerate age-related changes in collagen fibril diameter distributions in the common digital extensor tendon (CDET) of the forelimbs of young Thoroughbreds.
Animals—24 female Thoroughbreds.
Procedure—Horses were trained for 18 weeks (6 horses; short term) or 18 months (5 horses; long term) on a high-speed treadmill; 2 age-matched control groups (6 horses/group) performed walking exercise only. Horses were (mean ± SD) 24 ± 1 months and 39 ± 1 months old at termination of the shortterm and long-term regimens, respectively. Midmetacarpal CDET specimens were obtained and processed for transmission electron microscopy. Diameter and area of at least 1,000 collagen fibrils/specimen were measured by use of computerized image analysis. Mass-average diameter (MAD) of collagen fibrils and collagen fibril index were calculated for each horse.
Results—Collagen fibril MAD for the older horses was significantly less than that for the younger horses. Exercise did not significantly affect fibril diameter or distributions in either age group, and collagen fibril index did not differ significantly between groups.
Conclusions and Clinical Relevance—Age-related reduction in collagen fibril MAD agreed with findings for other tendons and species. Training did not accelerate age-related change in the CDET, in contrast to a reported decrease in collagen fibril MAD in the superficial digital flexor tendon of horses trained long term. Our results support the concept that the functionally distinct nature of the CDET and superficial digital flexor tendon in horses results in fundamentally different responses to high-speed exercise regimens. (Am J Vet Res 2005;66:564–568)
