Oxidant injury, nitric oxide and pulmonary vascular function: implications for the exercising horse.

This study investigates how oxidant injury, changes in pulmonary vascular function, and nitric oxide could contribute to possible respiratory diseases in exercising horses, emphasizing the complex interplay of these factors and their implications on a horse’s athletic ability.

Pulmonary Adaptations and Consequences in Exercising Horses

• Horses have certain physiological adaptations like a thin, strong pulmonary blood-gas barrier, large pulmonary functional reserve and high maximum oxygen uptake. These adaptations contribute to their athletic capability.
• High pulmonary artery pressure enhances lung function in horses. But, excessive pressure can lead to stress failure of lung capillaries, a condition possibly leading to exercise-induced pulmonary haemorrhage (EIPH) – a pathology commonly found in horses that exert intense efforts.

Role of Reactive Oxygen Species (ROS)

• ROS, an essential part of the mammalian inflammatory response, is released during tissue injury. While these are necessary for cellular defences against pathogens, an overproduction or lack of proper antioxidant defenses can cause oxidant damage to healthy tissues.
• Within the lung, ROS can directly cause damage to structures and initiate the release of other inflaming mediators like proteases and eicosanoids.

Impact on Vascular Endothelial Cells and Nitric Oxide (NO)

• Vascular endothelial cells, found in the lungs, are susceptible to oxidant injury from ROS. Such injuries can potentially lead to the destruction of the pulmonary blood-gas barrier and trigger activities of vasoactive substances, which eventually raises pulmonary vascular resistance.
• ROS can degrade nitric oxide, a vasodilator within the pulmonary circulation. Consequently, the reduced nitric oxide coupled with exercise can increase the chances of stress failure of pulmonary capillaries, another factor contributing to EIPH.

Implications

• The collective influence of oxidant injury, pulmonary vascular function, and nitric oxide levels could contribute to respiratory diseases in exercising horses.
• The findings from this study can help better understand, manage, and potentially prevent the onset of these conditions in horses, particularly active ones.