Abstract

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.