Transfer of tritiated water, tyrosine, and propanol from the nasal cavity to cranial arterial blood in rats

Respiration cools the nasal vein blood. This may, via counter current transfer in the cavernous sinus/carotid artery complex, cool the brain arterial blood and, therefore, decrease the brain temperature during heat stress. We investigated the possible local transfer of substances from the nasal cavities to the brain via a similar transfer between nasal venous blood and brain arterial blood. Tritiated water (TW). H-3-tyrosine (T) and C-14-Dropanol (P) were infused into the nasal cavity of anesthetized rats that had two catheters inserted into the same, occluded carotid artery, one pointing towards the head, the other towards the heart. Continuous, parallel blood samples were collected throughout 30-s periods for 10 min, and the radioactivity measured in the separated plasma. After nasal application of TW, the radioactivity increased in the head arterial plasma samples compared with the parallel heart samples. When recirculation to the general circulation was diminished, a larger and significant difference was found for all three substances during the last 5 min of the collection period. No difference between the parallel samples was observed after intravenous administration of the three substances. Absorption of all three substances from the nasal cavity was rapid and high. The results indicate that local transfer takes place between the venous and arterial blood in the head, probably in the area of the cavernous sinus-carotid artery complex, which in rat and man lacks a Rete Mirabile. The local transfer raises the possibility of treating brain diseases in man locally through nasal application of drugs.