BIBP 3226 inhibition of nicotinic receptor mediated chromaffin cell secretion

( R)- N 2-(diphenacetyl)- N-[(4-hydroxyphenyl)methyl]-argininamide (BIBP 3226) is a selective neuropeptide Y Y 1 receptor antagonist with structural similarity to the C-terminal tripeptide of neuropeptide Y. Based on this similarity we questioned whether BIBP 3226 could act as an agonist. Incubation of BIBP 3226 with bovine chromaffin cells in culture results in the inhibition of nicotinic receptor-stimulated catecholamine secretion (IC 50=2.4 μM). The effect of BIBP 3226 is independent of neuropeptide Y action since the presence of neuropeptide Y in the culture medium does not alter the effect of BIBP 3226. BIBP 3226 decreased the efficacy of the nicotinic receptor agonist, 1,1-dimethyl-4-phenylpiperizinium (DMPP), but did not change its potency suggesting non-competitive inhibition. BIBP 3226 has a similar effect on nicotinic receptor-stimulated 45 Ca 2+ influx. BIBP 3226 does not inhibit [ 3 H ]norepinephrine release induced by high K + and its effect is not pertussis toxin-sensitive. We conclude that not only can BIBP 3226 act as a neuropeptide Y receptor antagonist in bovine chromaffin cells but also act as an agonist and inhibit catecholamine secretion.