Cyclic AMP (cAMP)
A key intracellular second messenger molecule produced when G-protein coupled receptors activate the enzyme adenylyl cyclase. Many peptide hormone receptors, including the GLP-1 receptor and GHRH receptor, signal through the cAMP pathway. Elevated cAMP levels trigger downstream protein kinase activation and cellular responses.
Technical Context
cAMP is synthesised from ATP by adenylyl cyclase (activated by Gαs-coupled GPCRs) and degraded by phosphodiesterases (PDEs). The GLP-1 receptor signals primarily through cAMP/PKA: GLP-1R activation → Gαs → adenylyl cyclase → cAMP → PKA → CREB phosphorylation → insulin gene transcription; cAMP also activates Epac2, which contributes to insulin granule exocytosis. The GHRH receptor also signals through cAMP to stimulate GH gene transcription and secretion. Somatostatin receptors couple to Gαi, which inhibits adenylyl cyclase and reduces cAMP, explaining somatostatin's inhibitory effects. The cAMP/PKA pathway is thus a convergence point for both stimulatory and inhibitory peptide hormone signalling.