Continued artificial selection for running endurance in rats is associated with improved lung function

Kirkton SD, Howlett RA, Gonzalez NC, Giuliano PG, Britton SL, Koch LG, Wagner HE, Wagner PD. Continued artificial selection for running endurance in rats is associated with improved lung function. J Appl Physiol 106: 1810-1818, 2009. First published March 19, 2009; doi:10.1152/japplphysiol.90419.2008.-Previous studies found that selection for endurance running in untrained rats produced distinct high (HCR) and low (LCR) capacity runners. Furthermore, despite weighing 14% less, 7th generation HCR rats achieved the same absolute maximal oxygen consumption ((V) over dotO(2max)) as LCR due to muscle adaptations that improved oxygen extraction and use. However, there were no differences in cardiopulmonary function after seven generations of selection. If selection for increased endurance capacity continued, we hypothesized that due to the serial nature of oxygen delivery enhanced cardiopulmonary function would be required. In the present study, generation 15 rats selected for high and low endurance running capacity showed differences in pulmonary function. HCR, now 25% lighter than LCR, reached a 12% higher absolute (V) over dotO(2max) than LCR, P < 0.05 (49% higher (V) over dotO(2max)/kg). Despite the 25% difference in body size, both lung volume (at 20 cmH(2)O airway pressure) and exercise diffusing capacity were similar in HCR and LCR. Lung volume of LCR lay on published mammalian allometrical relationships while that of HCR lay above that line. Alveolar ventilation at (V) over dotO(2max) was 30% higher, P < 0.05 (78% higher, per kg), arterial PCO2 was 4.5 mmHg (17%) lower, P < 0.05, while total pulmonary vascular resistance was (insignificantly) 5% lower (30% lower, per kg) in HCR. The smaller mass of HCR animals was due mostly to a smaller body frame rather than to a lower fat mass. These findings show that by generation 15, lung size in smaller HCR rats is not reduced in concert with their smaller body size, but has remained similar to that of LCR, supporting the hypothesis that continued selection for increased endurance capacity requires relatively larger lungs, supporting greater ventilation, gas exchange, and pulmonary vascular conductance.