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

Abstract

Among the many responses to GH administration is suppression of voluntary feed intake (FI) in some species, attributed to improvement in the efficiency of nutrient utilization and, therefore, reduced need for ingested substrates. Commercial broiler chickens have been genetically selected for generations for rapid growth, realized largely via the major correlated response of increased voluntary feed consumption. Neuropeptide Y (NPY) and monoamines play very important roles in the central regulation of feeding. Preliminary 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 the 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 GH in a pulsatile pattern for 7 days at 0, 10, 50, 100 or 200 µg/kg body weight per day. Hypothalamic NPY and epinephrine (EP) concentrations decreased in a dose-related manner with GH. At the highest dosage, voluntary FI decreased 19% (P<0·05) and hypothalamic NPY mRNA decreased approximately 50% in the infundibular nuclei and midline region (P<0·0001). In contrast, birds pairfed to the high-GH dosage group did not 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 mediators of the appetite-suppressive effect of GH.

Permeation of Growth Hormone across the Blood-Brain Barrier

“…In addition, GH alters appetite and feeding behavior (20). It is not known whether these effects occur outside or within the BBB, and if inside, whether by direct action or indirect alteration of other neurotransmitters in response to GH.…”

Growth hormone improves lipoprotein concentration and arylesterase activity in mice with an atherogenic lipid profile induced by lactalbumin

“…Noteworthy is the observation of the diminution of body fat levels due to GH administration despite the increase in feed intake. Previous studies have demonstrated that the effect of GH on food intake is species, age and sex dependent ( 49 , 50 ) . Our own study shows that GH administration diminished body fat levels in all animals independently of age and sex, and paradoxically there was an increased feed intake in adult mice and to a greater magnitude in males than in females, suggesting important effects of sex and ageing hormone regulation.…”

Type-dependent differential expression of neuropeptide Y in chicken hypothalamus (Gallus domesticus)

“…These findings, together with our results, suggest that the higher mRNA level of hypothalamic NPY in the layer-type chicken is due to increased behaviors, including feeding behaviors. On the other hand, growth hormone inhibits the hypothalamic NPY in chickens (Wang et al, 2000), and the peak of growth hormone secretion appears at the age of 14~28 d (Burnside and Cogburn, 1992). Body weight of the meat-type chicken was significantly greater than that of the layer-type chicken at the same age, suggesting a rapid growing rate in the meat-type chicken.…”