EFFECTS OF THE SYMPATHETIC NERVOUS SYSTEM AND THE ADRENAL MEDULLARY HORMONES ON DOG HIND LIMB BLOOD FLOW AFTER HAEMORRHAGE

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Abstract
The contributions of the sympathetic nervous system and the adrenal medullary catecholamines to the response of dog hind limb resistance vessels to haemorrhage were examined. Anaesthetized dogs were bled either 30% or 45% of blood volume. There was little difference between the vascular conductance response in untreated hind limbs and sympathectomized limbs. Conductance in limbs that had been both sympathectomized and alpha-adrenergically blocked with phenoxybenzamine was markedly above that of untreated limbs. Blood flow in both the untreated limbs and the sympathectomized limbs was closely similar to that predicted from the pressure-flow curve for the hind limbs obtained in non-bled dogs. Flow was higher than predicted in the limbs with combined sympathectomy and alpha-adrenergic blockade. It is concluded that the sympathetic nervous system exerted little vasoconstrictive influence after haemorrhage, but that circulatory catecholamines exerted a strong vasoconstrictive influence that was opposed in the normal limbs by an almost equally powerful vasodilatory force of undetermined origin.