with either glutaminase or g-glutamyltranspeptidase (19).
Moreover, incubation of L-theanine with homogenate from
rats kidney, but not from rats small intestine, liver, and brain,
increased the concentration of ethylamine and glutamic acid
(8,20). Thus, L-theanine may be hydrolyzed to ethylamine and
glutamic acid in vivo. This assumption is supported by our
observation that only 2.4–3.1% of ingested L-theanine was
excreted by urine in contrast to the relatively high excretion of
ethylamine and glutamic acid (Table 3). This corresponds to the
observation in rats, where only 2.1% of the orally ingested
L-theanine (100 mg) was excreted (8). However, in contrast to
ethylamine, the amounts of glutamic acid observed in vivo
cannot be completely ascribed to orally ingested L-theanine,
because glutamic acid is continuously formed in amino acid
metabolism by glutaminase, glutamate dehydrogenase, and the
transamination of 2-oxoglutarate (21).