Nitric oxide synthase inhibition does not affect the exercise-induced arterial hypoxemia in Thoroughbred horses.

The research article focuses on determining the role of endogenous nitric oxide (NO) production in arterial hypoxemia experienced by Thoroughbred horses during exercise. The study found no significant alterations in the exercise-induced arterial hypoxemia, despite the inhibition of NO synthase.

Research Methodology

• The research involved studying arterial blood-gas variables in seven healthy Thoroughbred horses.
• The horses were monitored while at rest and also during increasing exercise intensity leading to galloping at their maximum heart rate.
• The tests were performed under control conditions and with the administration of L-NAME which inhibits the production of nitric oxide.
• Two sets of experiments were conducted, one week apart, on a random order basis.

Findings and Interpretations

• Administration of L-NAME, at rest, resulted in systemic hypertension, pulmonary hypertension, and slower heart rate.
• During a 120 second period of galloping at maximum heart rate, significant arterial hypoxemia, hemoglobin desaturation, hypercapnia, increased body temperature, and acidosis were observed. These symptoms occurred irrespective of whether nitric oxide synthase was inhibited or not.
• There was no statistically significant difference found between the control and NO synthase inhibited treatments. However, the increase in hemoglobin concentration caused by exercise was significantly tempered in the NO synthase inhibition experiments, leading to a noticeable decrease in the increment of arterial oxygen content.

Implications of Findings

• The results indicate that, while L-NAME administration does not affect pulmonary gas exchange in exercising horses, it could affect the contraction of the spleen.
• This effect on the spleen could in turn reduce the rise in hemoglobin concentration and arterial oxygen content, potentially limiting the performance of the horses at higher workloads.