Reduction of renal function in exercising horses

Glomerular filtration rate (GFR) and extracellular volume (ECFV) were measu red before, during and after treadmill exercise in 5 trained Thoroughbred h orses (mean weight 483 kg). GFR/ECFV was determined by plasma disappearance of Tc-DTPA and ECFV was measured independently as thiocyanate space. Resti ng GFR averaged 1.6 1/min (3.3 ml/kg/min) and fell by over 40% during exerc ise, moreover the fall was severe even during the first walk, prior to trot ting. The results suggest that rather than being protected, GFR is allowed to fall, even with mild exercise and that this is probably an adaptation to allow greater perfusion of muscle and skin. In man, GFR appears to be more resistant to the effects of exercise but it is hard to compare intensity o f exercise between such different species.