Ibutamoren mesylate (5 mg/kg/day) results in a statistically significant increases body weight gain and increases serum IGF-1 and GH levels in dogs. Ibutamoren mesylate results in no significant increase in CSF IGF-1 or GH levels on days 7 or 15 of the study. Pretreating mice with GH blocks activation of these neurons by Ibutamoren mesylate (50 μg, i.p.). In the knockout mice, both GH and octreotide fail to inhibit Ibutamoren mesylate activation of arcuate neurons. Chronic oral administration of MK-0677 is associated with significant increases in GH and IGF-I levels that are maintained for the duration of the treatment. The GH profile following MK-0677 administration consists of episodic increases above control. MK-0677 significantly increases peak GH concentrations after oral administration. MK-0677 is a potent GH secretagogue that induces an immediate, large, long lasting increase in GH levels when administered orally or i.v.