Changes in blood-flow distribution during acute emotional stress in dogs

Summary

The changes in mesenteric, renal and hindlimb circulations during natural emotional stress have been investigated in dogs. Arterial pressure showed a moderate and generally byphasic rise. Heart rate rose markedly in most experiments, but tended to return towards control values more rapidly than blood pressure. Both mesenteric and renal vascular resistance were increased. In the kidney, however, the vasoconstriction was less constant and in most instances less pronounced than in splanchnic viscera. This suggested a relatively high “threshold” of the central neuron pools controlling the renal vessels. Also, the reduction of blood flow was less sustained in the renal than in meseteric vessels, probably because of the action of autoregulatory mechanisms in the kidney. In hindlimb skeletal muscles, emotional stress produced a vasodilatation which appeared to be independent of the blood pressure rise and, at least to a large extent, of muscle activity. Most likely, the effect was due to sympathetic vasodilator fiber activation, though there was some indication that vasoconstrictor fibers to skeletal muscles were also activated. The observation that muscle vasodilatation invariably occurred in response to very different emotional stimuli suggests that it is a component of most, if not all, emotional reaction patterns in dogs. Muscle vasodilatation was the primary vascular reaction to changes from resting condition to alertness, the mesenteric and renal vessels being only slightly constricted or unaffected.