Effectiveness of glyceryl trinitrate for enhancing digital submural perfusion in horses

Abstract

Objective.-To evaluate the clinical efficacy of topically administered glyceryl trinitrate (GTN) for inducing digital submural vasodilation in clinically normal horses. Animals.-7 adult horses without foot abnormalities. Procedures.-A concurrent-control crossover design was used to determine whether topical application of GTN ointment for prevention or treatment of laminitis would result in a detectable increase in digital perfusion. Heat-acclimated horses instumented for detection of wall surface temperature (HWST), mean systemic pressure, and heart rate were used. Horses were exposed to cold to induce digital vasoconstriction and treated with GTN in an attempt to induce digital vasodilation. Results.-Application of GTN failed to induce an increase in digital submural perfusion but did induce a mild decrease in mean systemic pressure. Conclusions and Clinical Relevance.-Topical application of 60 mg of GTN as a 2% ointment on the skin over the major vasculature in the region of the proximal interphalangeal joint (pastern) of horses was not effective in significantly increasing digital perfusion. A decrease in mean systemic pressure following treatment was observed, implying that the drug was absorbed. Use of GTN may result in a decrease in digital submural perfusion secondary to induction of peripheral constriction or a decrease in digital perfusion pressure.