Cardiovascular adjustments in limb retraction provoked by noxious stimulation in decerebrate and spinal cats. Evidence for a somatotopic organization.

Arterial blood pressure, heart rate and iliac blood flow were continuously recorded in 61 adult cats and their alteration induced by noxious stimulation of the interdigital spaces of the four limbs was studied in intact (anesthetized) and in decerebrate and spinal preparations. Noxious stimulation of any limb in the decerebrate animals provoked retraction 61% of the times and an increase of blood pressure and heart rate in approximately 80% of the stimulations. Stimulation of a hindlimb provoked an increase of blood flow in the same limb in about 80% of the stimulations, due to active vasodilation. Contralateral stimulation provoked a smaller increase of blood flow but with an increase in vascular resistance, indicating some degree of vasoconstriction. Stimulation of the forelimbs induced small increases of blood flow in the hindlimbs but the calculated vascular resistance was higher than the basal values, also indicating vasoconstriction. Neuromuscular blockade with gallamine did not affect the increase of hindlimb blood flow, suggesting a central regulation of the intricate distribution of blood to the limbs. The vasodilation was not due to activation of sympathetic cholinergic vasodilator neurons inasmuch as the blood flow responses were not affected by cholinergic blockade with atropine. In spinal animals, stimulation of any limb provoked small increases of blood pressure, extremely low degrees of tachycardia and an increase of hindlimb blood flow, with active vasodilation. Neuromuscular paralysis, however, abolished the adjustments of blood flow in the hindlimbs, indicating that metabolites and/or sensory information caused by muscle contraction induced them. In intact cats anesthetized with sodium pentobarbiturate, blood pressure and heart rate increased under noxious stimulation, although less than in the decerebrate animals. Nearly 40% of the stimulations provoked hypotension rather than hypertension. Blood flow increased due to stimulation of any limb but, as in the decerebrate preparation, there was active vasodilation in the ipsilateral hindlimb and vasoconstriction in the contralateral one.