INFLUENCE OF GLUCOCORTICOSTEROID HORMONES ON IMMUNE FUNCTIONS OF NORMAL AND CUSHING’S SYNDROME HORSES

Abstract

ABSTRACT

Influence of Glucocorticosteroid Hormones on Immune Functions of Normal and Cushing’s Syndrome Horses (April 2008)

Kaitlin Alyssa Gutierrez Department of Animal Science Texas A&M University

Research Advisor: Dr. Thomas H. Welsh, Jr. Department of Animal Science

The effect of glucocorticosteroid hormones on the equine immune system was assessed. Hypercortisolemia, associated with Cushing’s syndrome, is attributed with a decrease in equine immunity. Immunity may be compromised due to the effect of both synthetic (Dexamethasone) and naturally occurring (cortisol) glucocorticosteroid hormones. The glucocorticosteroid receptor antagonist RU486 decreases the unfavorable effects of hypercortisolemia. This study was designed to see if RU486 could modulate the negative effects of DEX. Whole blood samples were obtained via jugular venipuncture from 15 horses (4 breeds; 12 stallions; 3 geldings; 5-to-15 years of age; 450-800 kg BW) and were put into EDTA vacutainers. Separate cultures were established for each horse, and lymphocytes were isolated. Lymphocytes were plated at 100,000 cells per well and were incubated at 37oC for 96 hours. Lymphocytes were incubated in medium alone (DMEM/F12 1:1), medium containing concanavalin A (0-to-5 µg/mL), 1 µM of DEX, 1 µM of RU486, or any combination thereof. Cellular proliferation was determined by Promega CellTiter96 assay. Stimulation indices were determined by a comparison to conconavalin A at a concentration of 0 µg/mL. SAS was used to determine statistical differences between treatments. Conconavalin A showed a dose dependent increase in lymphoproliferation (P<.0001; initial and maximal increase at 0.3125 and 5 ug/ml ConA, respectively). DEX inhibited ConA induced lymphoproliferation (P<.0001). Specifically, DEX reduced basal proliferation by 20.2%. At 0.3125 and 5 µg/mL, proliferation was reduced by 34.4% and 23.9% respectively. The addition of RU486 counteracted the adverse effects of DEX (P<.0001). RU486 increased basal proliferation by 25.2% when compared to the inhibitory effect of DEX. Glucocorticosteroid antagonists may be used to study how immune functions may be suppressed in horses that are phenotypically hypercortisolemic due to the following factors: stress; DEX therapy; Cushing’s syndrome, or metabolic syndrome.