Effects of haemorrhage on the distribution of the peripheral blood flow in the rabbit

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Abstract
The effects of bleeding unanaesthetized rabbits by 26% of their blood volume on the blood flow in the portal, renal, muscle and skin beds were investigated in normal animals, in animals without functioning autonomic effectors, and in animals with section of the carotid sinus and aortic nerves. In animals without functioning autonomic effectors there was progressive vasodilatation during the 4 hr. following hemorrhage, which differed markedly in the different regional beds studied. The dilatation was greatest in the portal bed, followed by kidney and skin, but there was no significant change in the vascular resistance in muscle. In normal animals with intact reflexes the vascular resistance either increases or remains at control values, suggesting that reflex constrictor effects oppose locally acting dilator mechanisms. During the 4 hr. following hemorrhage reflex vasoconstrictor effects were greatest in kidney, followed by muscle, portal bed and skin. In animals with section of the carotid sinus and aortic nerves reflex constrictor effects were absent in the portal, muscle and skin beds, but significant vasoconstric-tion was still evident in the renal bed, though of smaller magnitude than in normal animals. The arterial baroreceptors are a major source of reflex activity following hemorrhage, but that other reflexo-genic zones contribute to the renal effects in normal animals.