39 The role of melanocortin-3 and -4 receptor in regulating appetite, energy homeostasis and neuroendocrine function in the pig C R Barb, A S Robertson1, J B Barrett, R R Kraeling and K L Houseknecht1 USDA-ARS, Russell Research Center, PO Box 5677, Athens, Georgia 30604, USA 1Pfizer Global Research and Development, Pfizer, Inc., Groton, Connecticut 06340, USA (Requests for offprints should be addressed to C R Barb; Email:
[email protected]) Abstract A recently discovered class of receptors, melanocortin-3 of NDP-MSH, which exhibited both a stimulatory and an and -4 receptor (MC3/4-R), are located within the brain inhibitory effect on GH secretion in fasted animals. and modulate feed intake in rodents. Stimulation of the Treatment with agouti-related peptide, a natural brain receptor (agonist) inhibits feed intake whereas blockade hormone that blocks the MC3/4R, failed to stimulate (antagonist) of the receptor increases intake. Our knowl- feed intake. These results do not support the idea that edge of factors regulating voluntary feed intake in humans endogenous melanocortin pays a critical role in regulating and domestic animals is very limited. i.c.v. administration feed intake and pituitary hormone secretion in the pig. of an MC3/4-R agonist, NDP-MSH, suppressed SHU9119 blocked the NDP-MSH-induced increase in (P,0·05) feed intake compared with controls at 12, 24, 48 cAMP in HEK293 cells expressing the porcine MC4-R and 72 h after treatment in growing pigs. Fed pigs were sequence without the missense mutation. The EC50 and more responsive to the MC3/4-R agonist then fasted IC50 values were similar to the human MC4-R, confirm- animals.