Growth hormone-releasing factor affects macronutrient intake during the anabolic phase of zinc repletion: total hypothalamic growth hormone-releasing factor content and growth hormone-releasing factor immunoneutralization during zinc repletion.
Growth hormone-releasing factor (GRF) is thought to perform two distinct functions within the brain. GRF synthesized in the median eminence (ME) stimulates the release of growth hormone (GH) from the pituitary, while GRF in the suprachiasmatic nucleus and median preoptic area (SCN/MPOA) may stimulate selection of dietary protein. These two functions may be coupled to regulate and enhance growth. During zinc repletion, a period characterized by increased protein intake and accelerated growth, we examined this coupling by measuring GRF peptide content in hypothalamic sites and neutralizing GRF function by infusing anti-GRF antibody into the hypothalamus during zinc repletion. Total GRF content and GRF content in the ME and SCN/MPOA were decreased in zinc-deficient (Zn-) rats compared to zinc-adequate (Zn+) rats (P < 0.05). There were no differences in GRF content during zinc repletion in either nuclei. Subsequently, we investigated the macronutrient feeding patterns of rats chronically infused with anti-GRF IgG into the lateral ventricle of the brain during zinc repletion. All Zn- and Zn+ rats administered anti-GRF IgG exhibited a reduction in protein intake during zinc repletion. The Zn- rats receiving anti-GRF-IgG consumed equal amounts of total diet compared to those receiving vehicle during the repletion period however they consumed less carbohydrate (P < 0.05) and considerably more fat (P < 0.02). There were no significant differences in carbohydrate or fat intake in Zn+ rats receiving anti-GRF antibody. These results suggest that GRF likely directs protein intake during normal growth, but may interact with additional appetite-controlling neuropeptides during zinc repletion.
Rains
T M
TM
Division of Nutritional Sciences, University of Illinois, Urbana 61801, USA.
Mangian
H F
HF
Liang
T
T
Cole
A C
AC
Beverly
J L
JL
Shay
N F
NF
D000824:Animal Nutritional Physiological Phenomena; D000818:Animals; D000906:Antibodies / Q000008:administration & dosage / Q000494:pharmacology; D003677:Deficiency Diseases / Q000378:metabolism; D013007:Growth Hormone-Releasing Hormone / Q000276:immunology / Q000502:physiology*; D007031:Hypothalamus / Q000187:drug effects / Q000378:metabolism; D007074:Immunoglobulin G / Q000008:administration & dosage / Q000494:pharmacology; D007276:Injections, Intraventricular; D008297:Male; D008473:Median Eminence / Q000378:metabolism; D011301:Preoptic Area / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D013493:Suprachiasmatic Nucleus / Q000378:metabolism; D015032:Zinc / Q000172:deficiency / Q000378:metabolism*
D000906:Antibodies; D007074:Immunoglobulin G; D013007:Growth Hormone-Releasing Hormone; D015032:Zinc