Some factors affecting oxygen tension in the brain and other organs

Abstract

Polarographic recording of cerebral oxygen tension was performed by means of gold-plated needle electrodes oriented stereotaxically in the forebrain of rabbits under light urethane anaesthesia. The indicated mean resting level of oxygen tension in grey matter was 13 mm Hg. Higher levels were recorded in cerebral ventricles and lower levels in white matter. O 2 breathing doubled the forebrain oxygen tension and N 2 or N 2 O reduced it nearly to zero. Inhalation of 80 % CO 2 and 20 % O 2 produced a threefold increase in oxygen tension. Forebrain oxygen tension was drastically reduced by inhalation of amyl nitrite and by carotid artery occlusion. The oxygen tension recorded in a small coagulated lesion or in dead forebrain was low, and no change resulted when the animal inhaled O 2 , N 2 or CO 2 . Intravenous injection of 1 to 10 μg adrenaline elicited a rise of up to 20% in forebrain oxygen tension and at the same time a fall in the oxygen tension recorded in the testis, lactating mammary gland or skin. Electrical stimulation (15 s) of the lateral or posterior hypo­-thalamus produced an elevation of forebrain oxygen tension persisting for a minute or more after the stimulus, suggesting a release of adrenomedullary adrenaline. Opposite effects were seen in the oxygen tension measured in testis, mammary gland or skin. Electrical stimulation of the cervical sympathetic nerve evoked an ipsilateral depression of forebrain oxygen tension amounting to nearly 50 % in some instances. Cervical sympathetic section did not influence resting forebrain oxygen tension.