Byte Sized Summary: The amino acid citrulline increases the blood concentration of the amino acid arginine more effectively than consuming the amino acid arginine directly. Yes, you read that right. (Ask a chemist to explain how.) Both of these molecules, when ingested, increase blood nitric oxide levels, are are thought to be responsible for the “pumped” muscle feeling at the gym, and other signalling pathways.
(Sidebar, if you are unfamiliar with the pump, Arnold describes it oh so well in Pumping Iron, Here.)
Researchers at the University Medical Centre in Hamburg-Eppendorf, Germany tested the acute effects of arginine and citrulline when consumed by healthy subjects.
Here is part of their conclusion:
L-Citrulline dose-dependently increased AUC and C(max) of plasma L-arginine concentration more effectively than L-arginine (P < 0.01). The highest dose of citrulline (3 g bid) increased the C(min) of plasma L-arginine and improved the L-arginine/ADMA ratio from 186 +/- 8 (baseline) to 278 +/- 14 [P < 0.01, 95% confidence interval (CI) 66, 121]. Moreover, urinary nitrate and cGMP were increased from 92 +/- 10 to 125 +/- 15 micromol mmol(-1) creatinine (P = 0.01, 95% CI 8, 58) and from 38 +/- 3.3 to 50 +/- 6.7 nmol mmol(-1) creatinine (P = 0.04, 95% CI 0.4, 24), respectively.
Educational note: AUC refers to the “area under a curve”, calculated as the integral of the area on a data plot. This is often used as a measure of concentration for time or dose-dependence in pharmacokinetic studies (in this case, plasma arginine).
Arginine and Citrulline have extensive use in body building communities. While they are popular for the “pump” mentioned above, some research suggests long term use may have side effects. More on that soon. Thanks for reading.