Thyroid, renal, and splanchnic circulation in horses at rest and during short-term exercise.

The research investigates the blood flow to various organs in healthy horses during rest and two levels of exercise. This is done using the microsphere technique and the results show significant changes in blood flow to these organs during exercise.

Research Method

• The study followed 9 healthy horses during states of rest and physical exertion at two different levels of intensity.
• 15-microm-diameter microspheres labelled with a radionuclide were injected into the horse’s left ventricle. These microspheres would travel with the blood and act as markers for tracking blood flow through different organs.
• The researchers monitored hemodynamic parameters, like heart rate, aortic pressure, right atrial and pulmonary pressures, to ensure that all measurements were made under steady-state conditions. The consistency between blood flow values for the left and the right kidneys affirmed proper mixing of the microspheres with blood.

Results at Rest

• While resting, the thyroid gland exhibited maximum blood flow. It was three times the blood flow received by the kidneys.
• Adrenal blood flow was only 25% of that in the kidneys.
• Within the gastrointestinal tract, the glandular stomach and pancreas were most perfused with blood, followed by the small intestine, ventral colon, and cecum.

Results During Exercise

• Exertion at 8 and 13 m/s significantly increased adrenal blood flow due to a considerable decrease in vascular resistance.
• The kidneys’ perfusion remained mostly unaffected during exercise at 8 m/s. However, an intense workout at 13 m/s significantly decreased kidney blood flow due to intense renal vasoconstriction.
• Peripheral vasoconstriction during exercise led to a significant reduction in blood flow to both the thyroid and pancreas.
• A similar significant vasoconstriction was observed throughout the gastrointestinal tract tissues during these workouts. This redirected blood flow away from these vascular beds.

Conclusions

• The findings reveal a clear link between the physical exertion level of horses and significant alterations in blood flow to several vital organs, mirroring the responses previously discussed in exercising ponies.
• Understanding these changes may provide valuable insights into equine physiology and could lead to improved training and veterinary care modalities.