EFFECTS OF HYPERCAPNIA ON THE VASCULAR RESISTANCE OF THE DOG'S HIND LIMB.

Abstract

In anesthetized dogs, the inhalation of 10 per cent carbon dioxide over a period of 1 to 3 min caused usually a monophasic response consisting of vasoconstriction in the perfused hind limb. It increased progressively during carbon dioxide inhalation and gradually disappeared after readmission of normal air. This vasoconstriction amounted to a mean increase of vascular resistance of +19 per cent. The vasoconstrictor response in the limb was reversed or strongly diminished after denervation of carotid sinuses and aortic arch and this indicates that the vasoconstriction resulted mainly from stimulation of chemoreceptors in the carotid and aortic bodies by carbon dioxide. The vasoconstriction was also reversed or strongly diminished by transection of the spinal cord, limb denervation, bretylium and hexamethonium; whereas bilateral adrenalectomy did not alter it significantly. It is evident, therefore, that reflex stimulation of vasoconstrictor center in the medulla produces vasoconstriction in the limb mainly by way of sympathetic nerves. It is also evident, that the liberation of catecholamines from adrenal glands is of minor importance.