Cardiovascular regulation by -atginine in the brain of rats Role of the brain renin-angiotensin system and nitric oxide

The effect of brain l -arginine on arterial pressure was investigated by injecting l - or d -arginine into the cerebral ventricles of male Wistar rats that were anesthetized with urethane. Intracerebroventricular (ICV) injection of 1 μ mol l -arginine reduced the arterial pressure and the abdominal sympathetic nervous activity (SNA), whereas the injection of 10 μ mol l -arginine induced a transient pressor response and reduced both the heart rate and SNA. Although ICV injection of 1 μ mol d -arginine had no effect on cardiovascular function or SNA, injection of 10 μ mol of this enantiomer elicited a transient pressor response, similar to that induced by 10 μ mol l -arginine, followed by a persistent increase in arterial pressure and a corresponding increase in SNA. ICV pretreatment with the nitric oxide synthase inhibitor N G -monomethyl l -arginine abolished the vasodepressor response and reduced the inhibition of SNA induced by ICV injection of 1 μ mol l -arginine; such pretreatment increased the arterial pressure, heart rate, and SNA measured 30 min after ICV injection of 10 μ mol l -arginine. ICV pretreatment with the angiotensin II type 1 receptor antagonist CV-11974 inhibited the pressor response to 10 μ mol l -arginine and the first phase of the pressor response to 10 μ mol d -arginine. Intravenous pretreatment with the α 1 -adrenoceptor blocker bunazosin hydrochloride abolished the pressor response to 10 μ mol l -arginine and both phases of the pressor response to 10 μ mol d -arginine. Brain l -arginine thus appears to exert pressor actions through stimulation of the brain renin-angiotensin system and peripheral SNA. However, these actions may be attenuated by l -arginine-derived nitric oxide.