Renal tubular function in horses during submaximal exercise.

The research examines how submaximal treadmill exercise influences renal (kidney) function in horses, specifically its effects on urine flow and excretion of certain substances.

Study Design

• Two trials were conducted on six unfit mares with a week interval. In one trial, the mares were exercised on a treadmill inclined at 6 degrees for an hour at 55-60% of their maximal heart rate. In the other trial, the mares were just subjected to a parallel control with no exercise.

Main Findings

• The research found several exercise-induced changes. Plasma osmolality and the levels of potassium in plasma significantly increased.
• Also observed was an increased urine flow by 45%, Sodium (Na+) excretion by 371%, Potassium (K+) excretion by 57%, and Na+ and K+ clearance increased by 391% and 33% respectively. This also led to an increase in the fractional Na+ excretion by 320% and osmotic clearance by 32%.
• However, exercise decreased the levels of Chloride (Cl-) in the plasma and Cl- excretion by 46%, Cl- clearance by 41%, and fractional Cl- excretion by 47%.
• Despite these changes, there was no observed change in glomerular filtration rate, fractional K+ excretion, and free water clearance during exercise.

Role of Hormones

• The concentration of atrial natriuretic peptide, a hormone that helps regulate blood pressure and the balance of fluids and salts, increased during exercise. At rest, the average concentration was around 11 pg/ml, but it rose to a peak of 40 pg/ml, an increase of 264%, after 40 minutes of exercise.
• Similarly, plasma renin activity increased by 66%, leading to a significant increase in the plasma aldosterone concentration by 760%. Both these hormones are involved in regulating blood pressure.
• Exercise also induced a steady increase in Vasopressin concentration, a hormone that regulates water in the body.

Conclusion

• The study concludes that submaximal exercise in horses causes an increase in urine flow and sodium excretion. These changes are associated with a concurrent increase in the plasma concentration of atrial natriuretic peptide.