Neuropeptide Y inhibits chromaffin cell nicotinic receptor-stimulated tyrosine hydroxylase activity through a receptor-linked G protein-mediated process

Acetylcholine stimulation of bovine chromaffin cells results in increased norepinephrine and epinephrine secretion accompanied by a corresponding increase in synthesis. The addition of neuropeptide Y (NPY) to the culture medium prevents the increase in catecholamine synthesis but not secretion. Treatment of chromaffin cells with nicotine produces a concentration-dependent increase in tyrosine hydroxylase activity (IC50 = 1.2 mu M) that is reduced if NPY is present during stimulation. Tyrosine hydroxylase activity decreases in a concentration-dependent fashion if increasing amounts of NPY are included in the culture medium, IC50 = 0.2 nM. Treatment with pertussis toxin completely prevents the effect of NPY. The rank order of potency for inhibition of tyrosine hydroxylase activity is NPY greater than or equal to [Leu(31),Pro(34)]NPY greater than or equal to peptide YY > NPY2-36 > NPY13-36 > NPY18-36 greater than or equal to NPY26-36 much greater than NPY1-30, suggesting a NPY-Y1 receptor subtype. Examination of the effect of NPY on nicotine stimulation of chromaffin cell protein phosphorylation showed that NPY produces a concentration-dependent decrease in a 60-kDa protein, IC50 = 6.4 nM. The effect of NPY is pertussis toxin-sensitive. The rank order of potency is [Leu(31),Pro(34)]NPY greater than or equal to NPY much greater than NPY18-36. Immunoprecipitation confirmed the identity of the 60-kDa protein as tyrosine hydroxylase.