H. Cadas et al., OCCURRENCE AND BIOSYNTHESIS OF ENDOGENOUS CANNABINOID PRECURSOR, N-ARACHIDONOYL PHOSPHATIDYLETHANOLAMINE, IN RAT-BRAIN, The Journal of neuroscience, 17(4), 1997, pp. 1226-1242
It has been suggested that anandamide (N-arachidonoylethanolamine), an
endogenous cannabinoid substance, may be produced through Ca2+-stimul
ated hydrolysis of the phosphatidylethanolamine (PE) derivative N-arac
hidonoyl PE. The presence of N-arachidonoyl PE in adult brain tissue a
nd the enzyme pathways that underlie its biosynthesis are, however, st
ill undetermined. We report here that rat brain tissue contains both a
nandamide (11 +/- 7 pmol/gm wet tissue) and N-arachidonoyl PE (22 +/-
16 pmol/gm), as assessed by gas chromatography/mass spectrometry. We d
escribe a N-acyltransferase activity in brain that catalyzes the biosy
nthesis of N-arachidonoyl PE by transferring an arachidonate group fro
m the sn-1 carbon of phospholipids to the amino group of PE. We also s
how that sn-1 arachidonoyl phospholipids are present in brain, where t
hey constitute similar to 0.5% of total phospholipids. N-acyltransfera
se activity is Ca2+ dependent and is enriched in brain and testis. Wit
hin the brain, N-acyltransferase activity is highest in brainstem; int
ermediate in cortex, striatum, hippocampus, medulla, and cerebellum; a
nd lowest in thalamus, hypothalamus, and olfactory bulb. Pharmacologic
al inhibition of N-acyltransferase activity in primary cultures of cor
tical neurons prevents Ca2+-stimulated N-arachidonoyl PE biosynthesis.
Our results demonstrate, therefore, that rat brain tissue contains th
e complement of enzymatic activity and lipid substrates necessary for
the biosynthesis of the anandamide precursor N-arachidonoyl PE. They a
lso suggest that biosynthesis of N-arachidonoyl PE and formation of an
andamide are tightly coupled processes, which may concomitantly be sti
mulated by elevations in intracellular Ca2+ occurring during neural ac
tivity.