Vol. 52, Issue 6, 1027-1033, 1997

Neuropeptide Y Inhibits Chromaffin Cell Nicotinic Receptor-Stimulated Tyrosine Hydroxylase Activity through a Receptor-Linked G Protein-Mediated Process

Jialin Zheng, Peijin Zhang, and Terry D. Hexum

Department of Pharmacology, University of Nebraska Medical Center, Omaha, Nebraska 68198-6260

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 µM) 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  [Leu³¹,Pro³⁴]NPY  peptide YY > NPY2-36>NPY13-36 > NPY18-36  NPY26-36  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 [Leu³¹,Pro³⁴]NPY  NPY  NPY18-36. Immunoprecipitation confirmed the identity of the 60-kDa protein as tyrosine hydroxylase.