L-ARGININE INFUSION INCREASES BASAL BUT NOT ACTIVATED CEREBRAL BLOOD-FLOW IN HUMANS

Nitric oxide is a potent vasodilator. Infusion of its precursor, L-arg inine, results in increased flow (CBF) in experimental animals. We exa mined the effects of L-arginine infusion on CBF in humans using positr on emission tomography and the quantitative (H2O)-O-15 method. Six sub jects received 500 mi of 0.9% NaCl solution, and six subjects received an infusion of L-arginine (16.7 mg/kg/min; 500 mg/kg). Before and aft er the i.v. infusion, paired CBF measurements were performed at baseli ne and with vibrotactile stimulation of the right hand. In scans perfo rmed without vibrotactile stimulation, mean whole-brain CBF increased from 34.9 +/- 3.7 mi 100 g(-1) min(-1) to 38.2 +/- 4.4 mi 100 g(-1) mi n(-1) (9.5%; p < 0.005) after L-arginine infusion. The temporal patter n of CBF changes differed from that of plasma growth hormone and insul in levels and of arterial pH. In contrast, in the saline group, mean w hole-brain CBF did not change significantly (35.8 +/- 5.9 mi 100 g(-1) min(-1) to 35.9 +/- 6.4 mi 100 g(-1) min(-1); 0.3%). Vibrotactile sti mulation produced significant focal increases in CBF, which were unaff ected by L-arginine infusion. L-arginine infusion was associated with an increase in plasma L-citrulline, a byproduct of nitric oxide synthe sis.