Plasma renin activity and plasma catecholamines in intact and splenectomized running and swimming beagle dogs

The influence of splenectomy in the dog on plasma catecholamine levels and plasma renin activity during treadmill running and swimming was investigated. Plasma catecholamines were measured by a radioenzymatic assay and plasma renin activity by a radioimmunoassay. Exercise consistently increased plasma catecholamine levels before and after splenectomy (range of increase:3-38 pmol·ml^-1). Swimming, however, was a stronger stimulus than running. No change in the ratio between noradrenaline and adrenaline was found. In intact dogs exercise results in a marked increase in hematocrit due to splenic contraction (range of increase 3-8 volume %), while renal blood flow and plasma renin activity remain virtually constant. In splenectomized dogs, exercise has been reported to induce a decrease in renal blood flow. In contrast to this known effect on renal blood flow, splenectomy did not affect plasma renin activity in treadmill running dogs. In swimming dogs, however, plasma renin activity was increased after splenectomy (range of increase 3.3-6.9 ng·Ang I·ml^-1·h^-1). Possibly, a threshold in sympathetic tone is required to increase renin release in the dog.