The effects of vasoactive amines found in the equine hindgut on digital blood flow in the normal horse.

The research paper is investigating the impact of certain compounds, specifically tryptamine and phenylethylamine, produced in a horse’s hindgut on blood flow in the horse’s feet. The researchers hypothesize that these compounds could affect blood circulation and contribute to a health issue called laminitis.

Objectives and Methodology

• The main aim of this research is to explore the effects of various amine compounds, specifically tryptamine and phenylethylamine, on the digital blood flow in horses. These compounds are formed by bacteria present in the equine hindgut, which refers to the large intestine and cecum of the horse. There is an assumption that disturbances in the blood flow in the foot, or the ‘digital blood flow’, have a critical role in the development of acute laminitis in horses, a condition that involves severe foot pain and lameness.
• To conduct this study, the selected amines were infused intravenously into horses, while their digital blood flow was measured using a procedure called Doppler ultrasound, an imaging method used to visualize blood flowing through blood vessels. Alongside this, the temperature on the surface of the foot was monitored, as were the plasma concentrations of 5-hydroxytryptamine (5-HT), a naturally occurring compound often referred to as serotonin.

Results

• The study found that the infusion of both tryptamine and phenylethylamine significantly reduced the digital arterial blood flow. Notably, the decrease did not influence the systemic arterial blood pressure or the horse’s heart rate. Furthermore, both compounds led to a decrease in the temperature of the dorsal hoof wall, or outer surface of the horse’s hoof, and increased levels of plasma 5-HT.
• The findings suggest that the introduction of these amines caused a reduction in digital blood flow, possibly via displacement of 5-HT from platelets. Platelets are a type of blood cell that plays a crucial role in blood clot formation. The researchers stipulate that the displacement of 5-HT could be linked to the vasoconstriction, or narrowing of blood vessels.

Conclusion and Future Directions

• The research concludes by noting that these specific amine compounds, if released into the bloodstream following a carbohydrate overload, could lead to selective vasoconstriction in the foot. This could potentially contribute to the development of conditions such as laminitis.
• As a next step, the researchers suggest that further investigations are required, particularly in ponies and horses naturally suffering from laminitis, to confirm their results and to explore if these amines could present a viable therapeutic target for the treatment of this disease.