Furosemide magnifies the exercise-induced elevation of plasma vasopressin concentration in horses.

The research article investigates whether the administration of furosemide prior to exercise results in larger increases in plasma arginine vasopressin concentrations than exercise alone in horses.

Study Design

• The study engaged six healthy, unfit adult mares in a randomized series of three 60-minute standard exercise tests on a treadmill to examine the effects of pre-exercise furosemide administration on plasma AVP levels. Furosemide is a diuretic used to prevent horses from bleeding during races.
• The horses underwent three different trials. In the first trial (FUR-4), they received an infusion of furosemide (1 mg kg-1) four hours before exercising and a placebo (10 ml saline) two minutes before exercising. In the second trial (FUR-2), horses received a placebo four hours before exercising and furosemide two minutes before exercising. In the third trial (CON), the horses received a placebo both four hours and two minutes before exercising.
• Each exercise test involved a sixty-minute run on an incline at a speed designed to produce a heart rate equal to 65% of the horse’s maximum heart rate.
• Blood samples were collected at rest, immediately prior to exercise, and at 15-minute intervals during the exercise trial. These samples were used to measure plasma AVP concentrations using a radioimmunoassay.

Findings

• In the CON trial, where horses received a placebo, there was a 561% increase in plasma AVP concentrations. The concentrations rose from an average resting state value of 6.3 pg ml-1 to 38.8 pg ml-1 at the conclusion of the one-hour run.
• In contrast, in the FUR-2 trial where horses were given furosemide two minutes before exercising, there was a 1185% increase in AVP levels, rising from an average value of 5.9 pg ml-1 at rest to 75.8 pg ml-1 post-exercise.
• These results effectively demonstrate that the administration of furosemide prior to exercise does increase plasma AVP concentrations to a greater extent than exercise alone in horses.