Exercise training-induced hypervolemia in greyhounds: role of water intake and renal mechanisms

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Abstract
If the chronic hypervolemia that accompanies endurance exercise training is due only to an increase in the rate of water intake or if there were contributions from renal mechanisms was determined. Four greyhound dogs, previously sedentary for 3 yr, were utilized. During the 28-day experiment each dog was trained on a treadmill ergometer for 14 consecutive days at 65% of its pretraining maximal work intensity. After training, plasma volume increased 472 ml (27.5%, P < 0.05). The rate of water intake increased 328 ml/day (33%, P < 0.05); urine output increased 87 ml/day (20.8%, P < 0.05). The mean resting 24 h values for clearance of Na increased 0.29 ml/min (90.3%, P < 0.05), and clearance of K decreased 1.51 ml/min (16.1%, not significant). Glomerular filtration rate, free water clearance and osmotic clearance were not significantly altered. Apparently, the primary mechanism for the exercise training-induced hypervolemia in dogs is a net positive water balance via increased water consumption without significant contribution from an increase in renal water reabsorption.