Sympathetic Restraint Of Blood Flow During Prolonged Exercise: 1178 Board #33 2:00 PM - 3:30 PM

Sympathetic nervous system restraint of skeletal muscle blood flow during dynamic exercise has been well documented. However, whether sympathetic restraint of muscle blood flow is constant throughout a prolonged exercise bout has not been established.

PURPOSE

To investigate the effect of exercise duration on α₂-adrenergic-receptor mediated restraint of skeletal muscle blood flow during prolonged constant-load exercise.

METHODS

Mongrel dogs were instrumented chronically with transit-time flow probes on the external iliac arteries and an indwelling catheter in a branch of the femoral artery. On separate days, a flow-adjusted dose of a selective α₂-adrenergic-receptor antagonist (rauwolscine) was infused following 5, 30 and 50 min of treadmill exercise at 3 and 6 mph. Hindlimb blood flow (HBF) and mean arterial pressure (MAP) were monitored continuously. Vascular conductance (VC) was calculated as HBF/MAP.

RESULTS

During exercise at 3 miles/h, rauwolscine infusion resulted in a greater (p < 0.05) increase in VC following 5 (49±9 %), compared to 30 (23±5 %) and 50 (23±5 %) min of exercise. In contrast, rauwolsince resulted in a similar increase in VC following 5 (19±4 %), 30 (16±5 %) and 50 (15±5 %) min of exercise at 6 miles/h.

CONCLUSIONS

These results suggest that exercise duration influences0 α₂-adrenergic-receptor mediated restraint of muscle blood flow. Futhermore, these results support the concept that exercise sympatholysis may be influenced by both the intensity and duration of exercise.

Supported by NHLBI and NSERC, Canada