Vascular responses in the equine digit.

The research study examines vascular responses in the horse foot, specifically investigating how the blood vessels of the digit respond to changes in blood flow and various drugs that can affect blood vessels. The findings showed a lack of auto-regulation or reactive hyperemia and different reactions to different drugs.

Methodology

The research was performed on 12 ponies who were anesthetized using pentobarbital. Their digital circulation, meaning the blood flow in the vessels of the foot, was isolated. The blood flow was either controlled using a pump or measured under natural perfusion, which means the normal circulation of blood. Rapid changes were made to blood flow and there were also stoppages to see the responses in the blood vessels.

Findings

• The study found no evidence of autoregulation or reactive hyperemia. Autoregulation is the ability of the blood vessels to widen or narrow to maintain constant blood flow despite changes in blood pressure. Reactive hyperemia is an increase in blood flow following a period of restricted blood flow. Hence, the pony digit blood vessels didn’t seem to have the ability to automatically adjust to changes or increase blood flow after restriction.
• Different drugs had different effects on the prevenous resistance, which is the resistance in the blood vessels before the blood reaches the veins. Acetylcholine, a neurotransmitter that helps to regulate many functions in the body, histamine, a substance that plays a role in several bodily functions including the inflammatory response, and two prostaglandins (E1 and E2) decreased the prevenous resistance. This means they made it easier for the blood to flow towards the veins.
• Epinephrine, also known as adrenaline, and serotonin, another neurotransmitter that helps to regulate mood, appetite, and sleep, brought about prevenous constriction, making it more difficult for blood to flow to the veins. Large doses of these two hormones reduced the size of the veins which can further restrict blood flow.
• Two other prostaglandins (A1 and F2alpha) had varying effects on the digital vasculature.

Comparison with canine forelimb skin vasculature

The researchers noted that the reactions they saw in the equine digital vasculature were similar to those seen in the vasculature of the skin of the forelimbs of dogs. This suggests that the equine (horse) foot may have similar mechanisms of blood flow regulation to another species, canines (dogs). This might be informative for future studies on blood flow in different animals.