GRF-induced feeding: evidence for protein selectivity and opiate involvement.
Growth hormone-releasing factor (GRF) is a hypothalamic peptide named for its ability to induce release of growth hormone from the anterior pituitary. GRF also acts as a neurotransmitter in the suprachiasmatic nucleus/medial preoptic area (SCN/MPOA) to stimulate food intake. The purpose of this series of experiments was to explore the nature of GRF-induced feeding, with a particular emphasis on macronutrient selectivity, and to examine the role of opiate activity in the paraventricular nucleus of the hypothalamus (PVN). Chow intake stimulated by GRF microinjection (1 pmol/0.5 microliters) into the SCN/MPOA was blocked by injection of methyl-naltrexone (3 micrograms/0.5 microliters) into the PVN. In animals habituated to macronutrient diets (Teklad, WI), GRF preferentially stimulated intake of protein at 2 and 4 h postinjection, whereas it had no effect on carbohydrate intake. Further, this effect was blocked by injection of naloxone (40 nmol/0.5 microliters) into the PVN. Microinjection of morphine (0, 1, 10, and 17 micrograms/0.5 microliter) into the PVN also specifically stimulated protein intake at 2 and 4 h postinjection. These results suggest that feeding derived from GRF actions in the SCN/MPOA is macronutrient selective, and is dependent on PVN opiate activity for expression.
Dickson
P R
PR
Department of Psychology, Dartmouth College, Hanover, NH 03755.
Vaccarino
F J
FJ
D000704:Analysis of Variance; D000818:Animals; D001931:Brain Mapping; D004040:Dietary Carbohydrates; D004044:Dietary Proteins; D005247:Feeding Behavior / Q000187:drug effects*; D005518:Food Preferences / Q000187:drug effects*; D013007:Growth Hormone-Releasing Hormone / Q000008:administration & dosage / Q000494:pharmacology*; D008297:Male; D008845:Microinjections; D009271:Naltrexone / Q000008:administration & dosage / Q000031:analogs & derivatives* / Q000494:pharmacology; D009292:Narcotic Antagonists / Q000494:pharmacology*; D010286:Paraventricular Hypothalamic Nucleus / Q000187:drug effects / Q000502:physiology*; D011301:Preoptic Area / Q000187:drug effects / Q000502:physiology*; D000644:Quaternary Ammonium Compounds; D051381:Rats; D017208:Rats, Wistar; D013997:Time Factors
D004040:Dietary Carbohydrates; D004044:Dietary Proteins; D009292:Narcotic Antagonists; D000644:Quaternary Ammonium Compounds; C032257:methylnaltrexone; D009271:Naltrexone; D013007:Growth Hormone-Releasing Hormone