Citrulline does not relax isolated rat and rabbit vessels

1. The study was prompted by the report of Ruiz E. and Tejerina T., describing endothelium-independent relaxation by L-citrulline via activation of particulate guanylate cyclase. 2. We compared the effects of L-citrulline and L-arginine in isolated aortic rings of rats and in isolated aortic, carotid and femoral artery rings of rabbits. 3. No significant relaxation to either L-citrulline or L-arginine was found in the concentration range of 10^-12 to 10^-3 M, while 3-morpholinosydnonimine hydrochloride (SIN-1, 10^-6 M) relaxed vascular tissues. 4. This study does not support the conclusion that L-citrulline has direct vasorelaxing action on vascular smooth muscle.