Agmatine crosses the blood-brain barrier

The question of whether agmatine crosses the blood-brain barrier has not been directly addressed, even though peripheral injection of this compound has produced behavioral responses in drug withdrawal, antidepressant, and anti-anxiety paradigms. Two models were used in this investigation. In the first, mice were injected intraperitoneally (i.p.) with agmatine (10, 50, or 300 mg/kg body weight) or arginine (600 mg/kg). After 1 or 3 hours, the animals were killed under gas anesthesia by perfusing their brains with ice-cold saline, and whole-brain agmatine was measured by HPLC. In parallel studies, a rhesus monkey was injected under gas anesthesia either intravenously (i.v.) with agmatine (30 mg/kg) or arginine (150 mg/kg), or intracerebroventricularly (i.c.v.) with agmatine (0.3 mg/kg i.c.v.). At varying times thereafter, cisterna magna cerebrospinal fluid (CSF) and blood plasma were collected and analyzed for agmatine levels. A rise in mouse brain agmatine was apparent after doses of 50 and 300 mg/kg i.p. Monkey CSF agmatine peaked in parallel with plasma agmatine 15 minutes following intravenous (i.v.) agmatine injection and at one sixth the level of the plasma peak. Monkey CSF agmatine peaked 43 minutes after i.v. arginine injection. The ventricular injection of agmatine resulted in a threefold sustained rise in blood plasma agmatine for at least 24 hours after injection. Therefore, agmatine and its precursor, arginine, cross the blood-brain barrier. CSF agmatine may be newly synthesized from peripherally injected arginine.