Studies on the hemodynamic changes induced by electrical stimulation of the vagosympathetic trunks in the dog

The effects of electrostimulation of the cephalic endings of the vago-sympathetic trunks on the systemic and perfusion pressure of the hind limb of the dog depend upon frequency, intensity and duration of the stimulus. The electrostimulation performed with stimuli of high frequency, low intensity and moderately long duration (rectangular waves of 1.5 V, 0.7 msec, 100 Hz) consistently elicited systemic hypertension and vasoconstriction. This response was completely abolished by pretreatment with guanethidine or hexamethonium. On the other hand, electrostimulation with stimuli of low frequency, high intensity and long duration (5 V, 1 msec, 10 Hz) produced systemic hypotension and vasodilatation in the perfused hind limb. These effects were completely blocked by atropine or hexamethonium, while guanethidine was unable to induce any modification. These findings suggest that electrostimulation of vagosympathetic trunks can evoke different hemodynamic responses depending upon the characteristics of the stimulus. The occurrence of a vasodilatation specifically blocked by atropine demonstrates that a purely cholinergic mechanism underlies such a reflex response.