Abstract
In order to elucidate the mechanism of the central hypertensive action of angiotensin II (ATII), the effects of ATII on the medullary neurons of rabbits were studied by the technique of electrophoretic application. ATII gave rise to excitatory effect on some neurons of medulla and this effect was antagonized by a specific ATII antagonist, 1-sarcosine-8-alanine-ATII. The ATII sensitive medullary neurons showed no specific response to acetylcholine, norepinephrine or isoproterenol, but there was a significant increase in the excitatory response to norepinephrine in comparison with the ATII non-sensitive neurons. The excitatory effect of ATII was not blocked by atropine, phentolamine and propranolol. The ATII sensitive neurons in the medulla apparently do not have a topograhically or functionally characteristic distribution related to the central vasomotor control mechanisms. The neurons in the area postrema did not respond to electrophoretically applied ATII, while microinjection of ATII in this region produced remarkable hypertensive responses. These results suggest that the mechanism of the central hypertensive action of ATII administered into the vertebral artery is primarily mediated by the chemoreception of the area postrema. The mechanism of central cardiovascular effect of ATII and of the effects of acetylcholine and catecholamines on the medullary neurons are discussed.
