Recipient Organization
LOUISIANA STATE UNIVERSITY
202 HIMES HALL
BATON ROUGE,LA 70803-0100
Performing Department
Veterinary Clinical Sciences
Non Technical Summary
Laminitis is a painful and debilitating condition of horses and ponies that has major economic and welfare implications. Anecdotal observations and the results of survey studies have indicated that most laminitis cases occur in horses and ponies kept at pasture. Risk for development of pasture-associated laminitis results from high nonstructural carbohydrate content of the pasture grass and from animal predisposing factors. Horses that have circulating concentrations of insulin (insulin resistance) are more likely to develop laminitis when grazing pasture grasses. Our research involves the study of laminitis by infusion of insulin and glucose intravenously. During laminitis, enzymes (metalloproteinases) that degrade the structures holding the hoof wall to the pedal bone are produced. Studies in our laboratory have shown that pentoxifylline is a potent inhibitor of these enzymes in the horse and that it effectively reduces lameness during laminitis. The goal for our studies is to evaluate the effects of pentoxifylline on laminitis caused by insulin.
Animal Health Component
(N/A)
Research Effort Categories
Basic
50%
Applied
(N/A)
Developmental
50%
Goals / Objectives
Laminitis has been induced by use of the prolonged euglycemic hyperinsulinemic clamp technique (p-EHC) in insulin resistant ponies and in Standardbred horses and, therefore, this model has been used to study laminitis associated with insulin resistance and endocrinopathic laminitis. Matrix metalloproteinase alterations and subsequent matrix degradation within the digital laminae play an integral part in the pathophysiology of laminitis. Studies in our laboratory have shown that pentoxifylline is a potent MMP inhibitor in the horse and that it effectively reduces lameness in a corn starch overload model of laminitis. Its effectiveness in the treatment/prevention of hyperinsulinemic laminitis has not been evaluated. Our goal for this study is to evaluate the effects of pentoxifylline on lameness using the p-EHC model of laminitis. 1. Equine laminitis will be successfully induced using the p-EHC technique. All horses will develop a euglycemic hyperinsulinemia. Blood will be collected throughout the study for assessment of glucose and insulin concentrations. 2. Control horses receiving saline will reach Obel grade 3 lameness at which time they will be euthanized. Horses receiving pentoxifylline will not become lame or will have reduced lameness compared with control horses and will be euthanized at 60 hours post-infusion.
Project Methods
Laminitis will be induced via euglycemic hyperinsulinemic clamp. Horses will be administered an intravenous bolus of insulin (45 milli IU per killogram body weight) followed by an infusion of insulin (6 milli IU per killogram body weight) and 50% dextrose to achieve a steady state euglycemic hyperinsulinemia for 60 hours or until Obel grade 3 laminitis is achieved, whichever occurs first. Horses in the treatment group will receive pentoxifylline (8.5 mg per kg body weight in 1L NaCl IV over 30 min) immediately prior to the insulin and 50% dextrose infusion, then every 12 hours until euthanasia. Horses in the control group will receive IL NaCl IV in the same manner. Four days prior to the study, horses will be taken off pasture and fed grass hay, chopped alfalfa, and water. During this time, blood samples will be drawn to establish resting serum insulin. After initiation of the insulin/50% dextrose infusion, blood glucose will be measured every 5 min for the first 3.5 hours followed by every 30 minutes until euthanasia. Serum insulin concentrations will be measured in both groups every hour for the first 15 hours followed by every 5 hours until euthanasia. Three blood samples for determining insulin sensitivity will be collected 10 minutes apart during the steady state period. Clinical signs (heart rate, respiratory rate, body temperature, mucous membrane color, capillary refill time, and digital pulses) will be monitored every 4 hours until euthanasia. Lameness will be evaluated every 2 hours until euthanasia and assigned an Obel grade (0-4). All horses will be euthanized via pentobarbital sodium (100 mg per kg body weight, IV) upon reaching Obel grade 3 lameness or at 60 hours post-initiation of infusion, whichever occurs first. Whole blood will be collected and immediately analyzed using a handheld glucometer. Serum insulin concentrations will be determined using a commercially available radioimmunoassay kit previously validated for use in the horse. Categorical data (Obel grade and comparison of blood glucose and serum insulin) will be analyzed non-parametrically using the Wilcoxon ranked sums test. Physical examination variables (heart rate, respiratory rate, and body temperature) will be expressed as mean + standard deviation and tested using the Shapiro-Wilk statistic to assess normality.