Even when there's already plenty of L-arginine in the blood, adding more still makes more nitric oxide—which is weird because you'd think the body would stop making more once it has enough. This suggests something else besides just having more原料 is controlling how much nitric oxide gets made.

Measures nitric oxide production (e.g., via plasma nitrite/nitrate or forearm blood flow) before and after intravenous infusion of L-arginine in individuals with baseline plasma L-arginine levels already above the known Km of eNOS, compared to saline placebo.

Tests whether increasing L-arginine concentrations above the Km of eNOS in isolated human endothelial cells leads to increased NO production, controlling for intracellular arginine transport and cofactor availability.

Examines whether individuals with genetically elevated plasma L-arginine (e.g., due to arginase deficiency) show proportionally higher NO production despite plasma levels far exceeding eNOS Km.

Quantifies the relationship between plasma L-arginine concentration and NO output across a wide range of concentrations, including above Km, to determine if the response curve deviates from Michaelis-Menten kinetics.

Determines whether NO production increases with L-arginine infusion in wild-type mice but not in eNOS-knockout mice, confirming eNOS-dependence and substrate override.