L-692429 (MK-0751) is a benzolactam derivative and a nonpeptidyl growth hormone secretagogue (GHS) agonist. L-692429 binds to G protein-coupled receptor with a Ki of 63 nM[1][2].

L-692429 stimulates intracellular calcium release, inositol phosphate (IP) turnover, cAMP-responsive element binding protein (CREB) activity, serum-responsive element activity and bioluminescence resonance energy transfer (BRET) activity with EC50 values of 26 nM, 47 nM, 60 nM, 63 nM and 58 nM, respectively[2].HeLa-T4 cells transiently expressing the flag epitope-tagged growth hormone secretagogue (GHS) receptor are treated with L-692429. The release of intracellular calcium is measured using fluorometry with the calcium indicator dye fluo-3/AM. Untransfected HeLa-T4 cells are unresponsive to L-692429 treatment, whereas HeLa-T4 cells transiently expressing GHS receptors demonstrate an increase in fluorescent emission after L-692429 treatment. A significant increase in luciferase activity after L-692429 treatment is seen, suggesting that activation of the GHS receptor stimulates the MAPK pathway[3].

When tested in anesthetized rats (Wistar rats), L-756867 inhibits L-692429 (100 μg/kg)-stimulated GH secretion in a dose-dependent manner. Complete inhibition is observed at an i.v. dose of 100 μg/kg of L-756867[1].

[1]. Cheng K, et al. Inhibition of L-692,429-stimulated rat growth hormone release by a weak substance P antagonist: L-756,867. J Endocrinol. 1997 Jan;152(1):155-8. [2]. Holst B, et al. Nonpeptide and peptide growth hormone secretagogues act both as ghrelin receptor agonist and as positive or negative allosteric modulators of ghrelin signaling. Mol Endocrinol. 2005 Sep;19(9):2400-11. [3]. Cunha SR, et al. Ghrelin and growth hormone (GH) secretagogues potentiate GH-releasing hormone (GHRH)-induced cyclic adenosine 3',5'-monophosphate production in cells expressing transfected GHRH and GH secretagogue receptors. Endocrinology. 2002 Dec;143(12):4570-82.