Phenotypic differences in cardiovascular regulation in inbred rat models of aerobic capacity

The Dark Aouti (DA) inbred strain of rats has superior aerobic treadmill ru nning capacity compared with the Copenhagen (COP) strain of inbred rats. Th is difference in aerobic capacity provides a model to explore the genetic b asis of variation in this trait. The present study evaluated intermediate p henotypic differences between 10 male COP inbred rats and 10 male DA inbred rats that might contribute to the difference in aerobic capacity between t he strains. Five autonomically regulated cardiovascular variables were eval uated during rest or exercise by measuring the response to autonomic antago nists. The DA rat had enhanced autonomic function for the regulation of per ipheral blood flow and cardiac output. Specifically, at rest the DA rats ha d significantly more sympathetic (123 +/- 8 vs. 99 +/- 7 beats/min) and par asympathetic (35 +/- 5 vs. 12 +/- 3 beats/min) tonus for heart rate control and more sympathetic support of blood pressure (70 +/- 7 vs. 38 +/- 6 mmHg ) compared with the COP rats. During three graded levels of treadmill exerc ise the DA rats had higher blood pressures (16% on average) and higher hear t rates (4% on average) relative to the COP rats. In addition, the DA rats had a 27% greater heart weight-to-body weight ratio compared with the COP s train of rats (3.63 +/- 0.08 vs. 2.85 +/- 0.07 g/kg). All five of these int ermediate phenotypes could participate as variables causative of the differ ence in treadmill running capacity between the DA and COP strains of rats.