Evidence of a role for neuropeptide Y and monoamines in mediating the appetite-suppressive effect of GH

Among the many responses to GH administration is suppression of voluntary f eed intake (FI) in some species, attributed to improvement in the efficienc y of nutrient utilization and, therefore, reduced need for Ingested substra tes. Commercial broiler chickens have been generically selected for generat ions for rapid growth, realized largely via the major correlated response o f increased voluntary tired consumption. Neuropeptide Y (NPY) and monoamine s play very important roles in the central regulation of feeding. Prelimina ry studies from our laboratory suggest that the appetite-suppressive effect of GH may be independent of its actions as a repartitioning agent, and may involve alterations in NPY expression at the pre-translational level. The purpose of this investigation was to explore the dose-response nature of th e appetite-suppressive effect of GH in juvenile broilers, and the possible involvement of NPY and monoamines in this process. A GH dose-response study was conducted using 8-week-old female broilers infused i.v. with CH in a p ulsatile pattern for 7 days at 0, 10, 50, 100 or 200 mug/kg body weight per day. Hypothalamic NPY and epinephrine (EP) concentrations decreased in a d ose-related manner with GH. At the highest dosage, voluntary FI decreased 1 9% (P<0.05) and hypothalamic NPY mRNA decreased approximately 50% in the in fundibular nuclei and midline region (P<0.0001). In contrast, birds pairfed to the high-GH dosage group did riot differ from controls, verifying that changes in NPY and monoamines were not secondary to reduced FI. We conclude that hypothalamic NPY and EP are likely candidates to explore further as m ediators of the appetite-suppressive effect of GH.