Persistence of Reflex Sympathetic Nervous System Activity in Man on Guanethidine or Reserpine

The effect of guanethidine and reserpine on the reflex sympathetic nervous system vasoconstriction in the calf and foot induced by a prolonged, generalized stimulus (body cooling for 1 hour) was studied in 12 normal subjects. Large daily clinical-doses of guanethidine (40 to 60 mg) or reserpine (1 mg) were given orally for 2 and 3 weeks, respectively. Foot and calf blood flows were measured by venous-occlusion, water plethysmography. Two control studies were performed on each subject, one before and another long after administration of the drug; body cooling produced significant decrease in calf and foot blood flow and increases in vascular resistance in both control studies. Subjects evidenced drug effects by a significant decrease in pulse rate, postural hypotension, hypotension following exercise, and blockade or attenuation of the Valsalva maneuver “overshoot.” The attenuation of the sympathetic nervous-system vasoconstrictor reflex to general body cooling was not statistically significant.Since large clinical doses of reserpine or guanethidine administered for 3 or 2 weeks, respectively, did not inhibit the reflex sympathetic vasoconstrictor effect of total body cooling, functional sympathetic neurotransmitter substance cannot be said to be absent.