Indexed on: 09 Feb '16Published on: 09 Feb '16Published in: Respiratory Physiology & Neurobiology
To test the hypotheses that erythropoietin (rhuEPO) treatment increases systemic hematocrit, maximal O2 uptake (V˙O2max, by elevated perfusive and diffusive O2 conductances) and performance five female horses (4-13 years) received 15IU/kg rhuEPO (erythropoietin) three times per week for three weeks. These horses had been splenectomized over 1 year previously to avoid confounding effects from the mobilization of splenic red blood cell reserves. Each horse performed three maximal exercise tests (one per month) on an inclined (4°) treadmill to the limit of tolerance; two control trials and one following EPO treatment. Measurements of hemoglobin concentration ([Hb] and hematocrit), plasma and blood volume, V˙O2, cardiac output as well as arterial and mixed venous blood gases were made at rest and during maximal exercise. EPO increased resting [Hb] by 18% from 13.3±0.6 to 15.7±0.8g/dL (mean±SD) corresponding to an increased hematocrit from 36±2 to 46±2% concurrent with 23 and 10% reductions in plasma and blood volume, respectively (all P<0.05). EPO elevated V˙O2max by 20% from 25.7±1.7 to 30.9±3.4L/min (P<0.05) via a 17% increase in arterial O2 content and 18% greater arteriovenous O2 difference in the face of an unchanged cardiac output. To achieve the greater V˙O2max after EPO, diffusive O2 conductance increased ∼30% (from 580±76 to 752±166mL O2/mmHg/min, P<0.05) which was substantially greater than the elevation of perfusive O2 conductance. These effects of EPO were associated with an increased exercise performance (total running time: control, 216±72; EPO, 264±48s, P<0.05). We conclude that EPO substantially increases V˙O2max and performance in the splenectomized horse via improved perfusive and diffusive O2 transport.