Nitric oxide precursor
L-arginine
Also searched as L-arginine.
The two enzymes compete for it, Which is why Supplementation is Unreliable — arginase activity, which rises with age and inflammation, diverts arginine away from nitric oxide production. Citrulline raises plasma arginine more effectively than arginine does, because it bypasses first-pass arginase.
In depth
The amino-acid substrate for nitric oxide synthesis. Substrate availability is rarely the limiting step in healthy people — which is why citrulline, which survives first-pass metabolism, often outperforms it.
What drives it
Micronutrient status increases it.
Dietary arginine and citrulline. Carried by the intermediary-metabolism, micronutrient and redox reviews. doi 10.3390/nu18132141 · PMC9967593
What it drives
It increases Blood flow (nitric oxide).
The two enzymes compete for it - arginase activity, which rises with age and inflammation, diverts arginine away from nitric oxide. Citrulline raises plasma arginine more effectively than arginine does, by bypassing first-pass arginase. Carried by the intermediary-metabolism, micronutrient and redox reviews. doi 10.3390/nu18132141 · PMC9967593
It increases Nitrogen clearance.
The urea cycle substrate. Carried by the intermediary-metabolism, micronutrient and redox reviews. doi 10.3390/nu18132141 · PMC9967593
It increases Rapid energy buffer.
33918657 — A creatine precursor. Carried by the intermediary-metabolism, micronutrient and redox reviews. doi 10.3390/nu18132141 · PMC9967593
It increases Glucagon cells.
Arginine is one of the strongest signals an alpha cell answers. Verbatim: 'Intravenous Arginine Stimulates Glucagon Secretion More Than Equimolar Alanine, Leucine, Glutamine, and Proline in Humans' (J Endocr Soc 2025, doi 10.1210/jendso/bvaf139). A second, independent stream in the perfused rat pancreas: arginine 'stimulated biphasic glucagon (IRG) secretion' (J Clin Invest 1974, doi 10.1172/JCI107823). intravenous arginine. doi 10.1210/jendso/bvaf139
Blends that modulate it
Each blend page names this pathway and carries the study behind its claim.
See it on the map
Open the causal map to follow this pathway upstream and downstream, arrow by arrow, each with its study.