Evaluation of the possible role of prostaglandin F2α in laminitis induced in horses by nasogastric administration of black walnut heartwood extract

Abstract

Objective - To provide insights into the role of prostaglandin F 2α (PGF2α) in the developmental stages of laminitis induced in horses by ingestion of black walnut heartwood extract (BWHE). Sample Population - 10 adult mixed-breed horses. Procedures - Horses were separated into 2 groups and were euthanatized at 12 hours after placebo (water) administration (control horses) or after BWHE administration and development of Obel grade 1 laminitis. Blood samples were obtained to determine plasma PGF2α concentrations hourly for the first 4 hours and subsequently every 2 hours after substance administration. Laminar arteries and veins were isolated, and responses to increasing concentrations of PGF 2α were measured before and after preincubation of blood vessels with prostanoid and thromboxane receptor antagonists SQ 29,548, SC-19220, and AH 6809. Results - Plasma PGF2α concentrations increased in horses given BWHE; the WBC count decreased concurrently. In control horses, PGF2α was a potent contractile agonist for laminar veins but not for laminar arteries. In horses given BWHE, PGF2α was similarly selective for laminar veins; however, the magnitude of PGF 2α-induced venoconstriction was less than that in control horses. After preincubation with SQ 29,548, laminar veins from control horses responded to PGF2α with a small degree of dilation, whereas laminar veins from horses given BWHE did not. Conclusions and Clinical Relevance - PGF2α may play a role in the inflammatory and vascular dysfunction associated with the prodromal stages of laminitis. Prostanoids such as PGF2α may be viable targets for the prevention of acute laminitis in horses.