Anandamide (
N-arachidonoylethanolamine) and six
fatty acid ethanolamides were synthesized and their pharmacological effects in mice were assessed using
catalepsy,
hypothermia and
pentobarbital-induced sleep prolongation as indices. The effects of
phenylmethylsulfonyl fluoride (PMSF) pretreatment on
anandamide effects were also evaluated and discussed in relation to inhibition of
anandamide amidohydrolase in mouse brain and liver. The cataleptogenic effect of
anandamide (ED50=6.0 mg/kg, i.v.) was 4 to 6 times more active than those of N-oleoyl- (ED50=26.5 mg/kg, i.v.) and N-linoleoylethanolamine (ED50=37.5 mg/kg, i.v.), although the peak time in the effect was observed within 1 min after i.v. administration. None of the
saturated fatty acid ethanolamides (N-myristoyl-, N-palmitoyl-, N-stearoyl- and N-arachidoylethanolamine) showed a positive response in the cataleptogenic effect even at a dose up to 40 mg/kg i.v.
Anandamide, N-linoleoyl-, N-oleoyl- and
N-myristoylethanolamine (10 mg/kg, i.v.) produced a significant
hypothermia (0.19 to 0.59 degrees C) at 5 to 15 min after administration. The duration of the effects of these ethanolamides was also relatively short.
Anandamide, N-linoleoyl-, N-oleoyl- and
N-palmitoylethanolamine (5 or 10 mg/kg, i.v.) significantly prolonged
pentobarbital-induced sleeping time by 148-207% of control sleeping time. The cataleptogenic effect of
anandamide was markedly potentiated by pretreatment of mice with PMSF (100 mg/kg, i.p.). The ED50 (mg/kg, i.v.) of
anandamide was 0.48 (0.24-0.96) in PMSF-pretreated mice. The pretreatment of mice with PMSF significantly decreased the metabolic clearance rate of
anandamide in microsomal fractions of liver and brain. Thus, the Vmax/Km values of brain and hepatic microsomes were 26 and 10%, respectively, as compared with those of control mice. The present study demonstrated that
anandamide and
N-acylethanolamines of
unsaturated fatty acids exhibited
cannabinoid-like effects in mice, and that
anandamide amidohydrolase has an important role in the pharmacological effects of
anandamide in vivo.