L-Arginine- 13 C 6 , 15 N 4 ,d 7 (hydrochloride) is the deuterium, 13 C-, and 15-labeled L-Arginine hydrochloride. L-Arginine hydrochloride ((S)-(+)-Arginine hydrochloride) is the nitrogen donor for synthesis of nitric oxide, a potent vasodilator that is deficient during times of sickle cell crisis.