Metabolic effects of nitric oxide synthase inhibition during exercise in the horse.

This research investigated the metabolic effects of inhibiting nitric oxide synthase (NOS) during exercise in Thoroughbred horses, particularly focusing on lactate production.

Objective and methodology

• The aim of the research was to understand how inhibiting nitric oxide synthase (NOS) during exercise in horses influences lactate production. Nitric oxide synthase is an enzyme that plays a significant role in various physiological and pathological processes, most notably in regulating vascular resistance, neurotransmission, and immune response.
• A standard exercise test (SET), composed of three canters with periods of walking and trotting in between, was performed by five Thoroughbred horses on two different occasions: once as a control test and once as a test after NOS inhibition.
• The inhibition of NOS was carried out using Nphi-nitro-L-arginine methyl ester (L-NAME), a competitive inhibitor of NOS, administered at 20 mg per kg of the horse’s weight.

Findings

• The administration of L-NAME resulted in a significant increase in plasma lactate concentration in the tested horses, suggesting a metabolic effect from NOS inhibition during exercise. A rise from 5.7 (2.9) mmol L-1 to 11.8 (3.8) mmol L-1 in plasma lactate was observed.
• This increase in lactate production continued even after the administration of L-arginine, the substrate for NOS, implying that the increased production of lactic acid was not easily reversible.
• No significant differences were found in cardiac output (Q) or total body oxygen consumption (VO) between the control and test exercise tests.

Conclusion

• The study concludes that the non-specific inhibition of NOS isoforms can cause an increase in plasma lactate concentration during exercise in horses.
• However, the exact mechanism/s behind this trend remains uncertain, requiring further research to understand how inhibiting NOS during exercise influences metabolic processes in horses.