Antagonistic effect of N-methyltyramine on alpha(2)-adrenoceptor in mice

We examined the effect of N-methyltyramine (NMT) on alpha(2)-adrenoceptor. NMT (10(-8)-10(-3) M) inhibited the binding of [H-3]p-aminoclonidine to alp ha(2)-adrenoceptor dose-dependently. However, the IC50 value for NMT (5.53 x 10(-6) M) was higher than that for RX821002, an alpha(2)-adrenoceptor ant agonist (1.07 x 10(-8) M). RX821002 (5 mg/kg, i.p.) inhibited hypermotility induced by scopolamine (8 mg/kg, s.c.) in male ddY mice. NMT (20 or 100 mg /kg, i.p.) was found to have a dose-dependent inhibitory effect similar to that of RX821002. These findings indicate that NMT has the properties of an alpha(2)-adrenoceptor antagonist. However, the affinity of NMT for alpha(2 )-adrenoceptor is weaker than that of RX821002.