L-Arginine is the only biological substrate of nitric oxide synthase in a r
eaction yielding NO and L-citrulline as co-products. The resynthesis of L-a
rginine from L-citrulline has been observed in murine macrophages. However,
it is not known whether avian macrophages have a similar capacity for the
synthesis of arginine. The present studies were carried out to determine wh
ether L-citrulline can support NO (measured as nitrite) production in the H
D11 cell, a chicken macrophage cell line. When added to media lacking L-arg
inine, L-citrulline supported a low level of nitrite accumulation: about 4
to 11% of the amount of nitrite formed from an equivalent concentration of
L-arginine. Aspartic acid was not limiting for NO production from citrullin
e.