104 Abstracts � Vol 30, No 2 (2010)

(100 mcg/kg). The plasma drug concentration-time profilewas analyzed using noncompartmental and compartmentalapproaches. Pharmacodynamics were measured using ADP-and collagen-induced platelet aggregation, and a model wasdeveloped to describe the observed drug effects.

RESULTSA two-compartment linear pharmacokinetic model de-scribed ketanserin’s plasma concentration-time profile; ter-minal half-life was 8.25 hour, volume of distribution was11.6 L, AUC was 5.98 mg�min/liter and clearance was0.01 L/min. Two populations of horses were identified,one in which ketanserin reduced agonist-induced plateletaggregation and one in which platelet responses were notaltered. In responding horses, ADP-induced platelet ag-gregation 8 hours after treatment decreased from71.2� 5.3% to 45.7� 9% and collagen-induced aggrega-tion from 72.3� 5.7% to 43.4� 17.2% (p< 0.001). After24 hours, platelet aggregation had returned to baselinevalues. Ketanserin pharmacodynamics exhibits a hysteresisand modeling suggests its dynamics can be described usingan indirect response model.

DISCUSSION, CLINICAL RELEVANCEAND CONCLUSIONA pharmacokinetic model was developed to describe theplasma concentration-time profile of ketanserin in healthyhorses, which suggests ketanserin’s time-course of activitycan be described by an indirect response model. Additionalstudies will be performed to determine whether alterationsin platelet and laminar microvascular function are related orindependent effects of the drug.

Cellular Proliferation Markersin Lamellar Tissue and Skin Measuredby Indirect ImmunofluorescenceRebecca Carter,1 Susan Megee,1 Julie Engiles,1

Makoto Senoo,2 and Hannah Galantino-Homer1,1Laminitis Institute, Department of Clinical Studies/New Bolton Center, 2Department of Animal Biology,School of Veterinary Medicine, University ofPennsylvania, Kennett Square, PA

TAKE HOME MESSAGEThe regional proliferative potential and state of lamellar tis-sue may be characterized by immunolocalization of p63and Ki-67, respectively.

INTRODUCTIONAbnormal epidermal proliferation may contribute to thepathology of chronic laminitis.

MATERIALS & METHODS (INCLUDINGSTATISTICAL ANALYSES)Postmortem (<1h) tissue from skin, coronary, proximal,middle and distal lamellae was collected from 3 horseswith no signs of laminitis (control) and 3 horses withchronic laminitis and P3 rotation. Indirect immunofluores-cence of paraformaldehyde-fixed, OCT-embedded cryo-sections using mouse monoclonal antibody againsthuman p63 (clone 4A4) and rabbit monoclonal antibodyagainst human Ki-67 (clone SP6) was used to determinerelative proportions of epidermal cells positive for p63(proliferative potential) and Ki-67 (cellular proliferation).Triplicate images were counted for each section and dataanalyzed by ANOVA.

RESULTSOverall, Ki-67 expression was higher in coronary comparedto skin and lamellar tissues and both p63 and Ki-67 weregreater in primary epidermal lamellae tips (closest to P3)compared to the base (closest to hoof wall). Consideringall tissues, laminitic horses had a lower percentage of epider-mal cells positive for p63 (40� 28%) and Ki-67(1.4� 3.1%)than controls (72� 19% and 3.0� 4.8%, respectively).

DISCUSSIONActively proliferating epidermal cells are located primarilyin coronary tissue, whereas cells with proliferative potentialare located throughout the hoof. Results indicate a decreasein epidermal proliferation during chronic laminitis; how-ever larger sample sizes should be analyzed to account forhigh inter-horse variability.

CLINICAL RELEVANCECharacterizing the proliferative state of normal and laminiticlamellar tissue will contribute to knowledge of laminitispathogenesis.

CONCLUSIONThese preliminary results indicate a decrease in epidermalcell proliferation during chronic laminitis.

Differences in Lamellar ProteinExpression During Laminitis Inducedby a 48h Prolonged Euglycemic-Hyperinsulinemic ClampRebecca Carter,1 Melody de Laat,2

Christopher Pollitt,1,2 and Hannah Galantino-Homer1,1Laminitis Institute, Department of Clinical Studies/New Bolton Center, School of Veterinary Medicine,University of Pennsylvania, Kennett Square, PA,2Australian Equine Laminitis Research Unit, School of