GHRP-6 is a synthetic growth hormone (GH) secretagogue and an agonist of the GH secretagogue receptor (GHS-R), which is also known as the ghrelin receptor.1,2,3,4 It inhibits binding of the GHS-R agonist MK-0677 to COS-7 cell membranes expressing human GHS-R type Ia (Ki = 1.9 nM) and binding of ghrelin to COS-7 cells expressing human GHS-R (Kd = 260 nM).2,3 GHRP-6 stimulates intracellular calcium mobilization in BHK cells expressing the human receptor (EC50 = 4.5 nM) and inositol phosphate production in COS-7 cells expressing the human receptor (EC50 = 0.83 nM).3 It also acts as a negative allosteric modulator of ghrelin signaling. GHRP-6 (0.03 μg/ml) induces release of GH, but not thyroid-stimulating hormone (TSH), luteinizing hormone (LH), or follicle-stimulating hormone (FSH), in isolated rat pituitary gland.1 It increases levels of GH, but not TSH, LH, FSH, or prolactin, in rat blood when administered subcutaneously at a dose of 50 μg. GHRP-6 increases food intake in rats when administered intracerebroventricularly at 0.3, 1, and 3 nmol
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